Ammeter to Voltmeter...who does it?

[Mattax]

Or I think I can skip connecting the 10ga. black wire with the fusible link to the starter relay and, instead, run it directly to the Coach/House battery charging solenoid, like the picture below. I think this will be a cleaner setup.

View attachment 1715235504

Yes, there a few different ways things can be arranged.
I don't know why the arrangement you currently have uses a fuse between the two batteries. There might be a reason a fast opening device was preferred.

The voltmeter as drawn will be on full time. Probably better to have a voltmeter wired to turn on with key in Run and accessory. no?

Is it possible to have a device that regulates the charging rate of the coach battery?

One advantage of an ammeter is that is shows charging, how much and when its done. The voltmeter only shows whether the alternator is producing enough power it can potentially charge the battery(s).
If the status of the second battery is important, might be worth having a second ammeter and/or voltmeter for that system. Obviously if you did an ammeter for it, it would be best with an external shunt. The ones for marine and aircraft will probably be the best, and most expensive, as they probably must meet instrumentation certifications for those uses. But those would be a couple of places to search for info and general availability.

 

[FLynes]

Yes, there a few different ways things can be arranged.
I don't know why the arrangement you currently have uses a fuse between the two batteries. There might be a reason a fast opening device was preferred.

I don't know either...my first thought was maybe it's there, in case the something happens to the solenoid, like the 12V power source spikes. I really have no idea.

The voltmeter as drawn will be on full time. Probably better to have a voltmeter wired to turn on with key in Run and accessory. no?

As it stands in stock form now, the ammeter is on full time...will it hurt the voltmeter, if it stays on full time? If so, I can find a switched 12V source under the dash and use it to power the voltmeter.

Is it possible to have a device that regulates the charging rate of the coach battery?

Yes, it is. It requires the removal of the existing Coach/House battery charging solenoid and replacing it with an updated charging system. It's on the list of things to do.

One advantage of an ammeter is that is shows charging, how much and when its done. The voltmeter only shows whether the alternator is producing enough power it can potentially charge the battery(s).
If the status of the second battery is important, might be worth having a second ammeter and/or voltmeter for that system. Obviously if you did an ammeter for it, it would be best with an external shunt. The ones for marine and aircraft will probably be the best, and most expensive, as they probably must meet instrumentation certifications for those uses. But those would be a couple of places to search for info and general availability.

The Coach/House battery has a second ammeter, located at the Power Distribution Center under the kitchen counter. When you press the switch, it gives you the health of the battery, and whether it's charging or not.

 

[Mattax]

I don't know either...my first thought was maybe it's there, in case the something happens to the solenoid, like the 12V power source spikes. I really have no idea.

Probably worth figuring out if this is standard practice and if so, why. A fuse or breaker, especially one thats 20 amps or less, between two batteries or between the alternator and the battery just seems odd.

As it stands in stock form now, the ammeter is on full time...will it hurt the voltmeter, if it stays on full time? If so, I can find a switched 12V source under the dash and use it to power the voltmeter.

Ammeters aren't on or off. It's the same as having a short piece of wire in the same location. If you go to the Chrysler MTSC page I linked, you'll see the ammeter consists a big plate with a connector on each end. A high resistance fine circuit is attached in parallel. When current moves through the plate, the needle in the fine circuit deflects.

Voltmeters are a through path with a very high resistance. The resistance limits flow through the meter to a tiny amount, but its there. It would be a slow drain on the battery.

AMC used the switched side of the fuse box on late SJs for the voltmeter lead. Not sure if it was fused on not, probably yes. I'm sure some folks earlier in this thread have discussed locations to tap.

Yes, it is. It requires the removal of the existing Coach/House battery charging solenoid and replacing it with an updated charging system. It's on the list of things to do.

The Coach/House battery has a second ammeter, located at the Power Distribution Center under the kitchen counter. When you press the switch, it gives you the health of the battery, and whether it's charging or not.

Interesting. Maybe it has a big resistor in it (load test).

 

[FLynes]

Probably worth figuring out if this is standard practice and if so, why. A fuse or breaker, especially one thats 20 amps or less, between two batteries or between the alternator and the battery just seems odd.

So I was completely talking out of my fourth point of contact about that fused wire....it isn't, and I'm surprised because I thought I knew this chassis cab inside and out. What I thought was a fuse holder is actually just a factory connector.

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Ammeters aren't on or off. It's the same as having a short piece of wire in the same location. If you go to the Chrysler MTSC page I linked, you'll see the ammeter consists a big plate with a connector on each end. A high resistance fine circuit is attached in parallel. When current moves through the plate, the needle in the fine circuit deflects.

I misspoke. What I should have said was that current passes through the ammeter at all times, whether the motorhome is running or not.

Voltmeters are a through path with a very high resistance. The resistance limits flow through the meter to a tiny amount, but its there. It would be a slow drain on the battery.

So I would definitely need to find a switched source, to avoid battery drain.

AMC used the switched side of the fuse box on late SJs for the voltmeter lead. Not sure if it was fused on not, probably yes. I'm sure some folks earlier in this thread have discussed locations to tap.

I don't know that I'll be able to use a switched source from the fuse block, like AMC had (I own a '76 CJ-5, so I know what you're talking about). This is the fuse block on the chassis cab.

Click For Full-Size Image.

Interesting. Maybe it has a big resistor in it (load test).

The Coach/House battery has a wire that runs to the 100A Charger/Converter which, in turn, is wired to the Power Distribution Center, so the resistor is probably in the Charger/Converter, because I don't remember seeing one in the Power Distribution Center.

 

[Mattax]

Cool.
Could the connector be a fusible link?
(the part leading to the solenoild)

I should have said was that current passes through the ammeter at all times, whether the motorhome is running or not.

Yes - if somethingis turned on, current will flow through it. Headlights for example, or radio if the key is in accessory position. Otherwise it's hot, but there's no flow.

Be interesting to see how the charger converter works and is wired with the condition test button.. Neat stuff. Ammeters on chargers seem to be pretty common.

 

[FLynes]

Cool.
Could the connector be a fusible link?
(the part leading to the solenoild)

Nope, it's just two wires with a connector. No idea why they have it like that, but the factory must have had a reason.

Yes - if somethingis turned on, current will flow through it. Headlights for example, or radio if the key is in accessory position. Otherwise it's hot, but there's no flow.

I think I'm misunderstanding you. How can it be hot but have no flow. What I understand as "hot" means that, when you put a test light on it, it lights up or, when you put a voltmeter on it, you get a reading. With the key out of the ignition, when I put my voltmeter on the bulkhead 10ga. red wire inside the cab, the one that connects to the fusible link, I get 12.85V. When I put it on the 10ga. black wire inside the cab, the one that connects to the alternator, I get 12.72V. This tells me that it's all hot, that there is current passing through those wires, as well as current passing through the ammeter.

Be interesting to see how the charger converter works and is wired with the condition test button.. Neat stuff. Ammeters on chargers seem to be pretty common.

So here's a pic of the back of the Power Distribution Center....the ammeter is pictured with the brass attaching clip. The white wire from it is connected to the other white wire, which goes to the panel light, and a green wire, which connects to a buss bar. The Charger/Converter green wire goes to the buss bar as well, as does the Coach/House battery.

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The 100A Smart Charger/Converter.

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[Mattax]

Nope, it's just two wires with a connector. No idea why they have it like that, but the factory must have had a reason.

Was just guessing. Some of the fusible links were attached to a connector - I assume for easier testing and replacement. Since that section of wire looks noticibley smaller diameter it could've been a link. Here's the one in my '67. It's dark blue 16 AWG and connects to the red 12 AWG wire.

I think I'm misunderstanding you. How can it be hot but have no flow. What I understand as "hot" means that, when you put a test light on it, it lights up or, when you put a voltmeter on it, you get a reading. With the key out of the ignition, when I put my voltmeter on the bulkhead 10ga. red wire inside the cab, the one that connects to the fusible link, I get 12.85V. When I put it on the 10ga. black wire inside the cab, the one that connects to the alternator, I get 12.72V. This tells me that it's all hot, that there is current passing through those wires, as well as current passing through the ammeter.

As your voltmeter shows, all of the main wires are hot. No electricty flows because there is no connection to ground. It has potential to flow, but isn't flowing. It needs a path to ground (and ground to battery or alt ground)
It's like the water in your house. All of the supply pipes have pressure in them. All of the faucets are shut, no one is doing laundry, so no water is flowing.

With no water running, pressure is pretty much the same any place we measure it.
What happens if a garden sprinkler is turned on?
->Water flows through hose to the sprinkler. Pressure in the hose goes from zero to same as the house. Water comes out the sprinkler and falls to the ground. House pressure stays about the same.

Electric current is like the water flowing. If water pressure in the house is 90 psi, its not going to drop much on the way to the sprinkler. Even washing potatoes in the kitchen sink, the pressure will not drop noticebly between the entrance and the faucets valves unless there is some sort of resistance such as caused by badly undersized pipes or heavy mineral build up.

The battery is like a storage tank. So if the house was using water from a storage tank, then as the water level drops, pressure will also drop. But as long as all the faucets are shut, all of the pipes will be at same pressure as the storage tank's outlet.

The alternator is like a well pump. It can supply water at higher pressure than the tank, but only as long as the amount it can flow isn't exceeded.

Hope that makes sense.

 

[Mattax]

BTW. This probably one reason why charging systems got ammeters. A voltmeter can not reveal if current is flowing to the battery. It will show if the alternator is not working (voltage will be battery voltage 12ish) or can't keep up with demand (between 12 and 14). But when showing 14 volts, we can only assume the battery is charging properly.

 

[FLynes]

Was just guessing. Some of the fusible links were attached to a connector - I assume for easier testing and replacement. Since that section of wire looks noticibley smaller diameter it could've been a link. Here's the one in my '67. It's dark blue 16 AWG and connects to the red 12 AWG wire.
View attachment 1715235650

Yep, my fusible link going to the bulkhead connector from the battery looks like yours, except that it's red.

As your voltmeter shows, all of the main wires are hot. No electricty flows because there is no connection to ground. It has potential to flow, but isn't flowing. It needs a path to ground (and ground to battery or alt ground)
It's like the water in your house. All of the supply pipes have pressure in them. All of the faucets are shut, no one is doing laundry, so no water is flowing.

With no water running, pressure is pretty much the same any place we measure it.
What happens if a garden sprinkler is turned on?
->Water flows through hose to the sprinkler. Pressure in the hose goes from zero to same as the house. Water comes out the sprinkler and falls to the ground. House pressure stays about the same.

Electric current is like the water flowing. If water pressure in the house is 90 psi, its not going to drop much on the way to the sprinkler. Even washing potatoes in the kitchen sink, the pressure will not drop noticebly between the entrance and the faucets valves unless there is some sort of resistance such as caused by badly undersized pipes or heavy mineral build up.

The battery is like a storage tank. So if the house was using water from a storage tank, then as the water level drops, pressure will also drop. But as long as all the faucets are shut, all of the pipes will be at same pressure as the storage tank's outlet.

The alternator is like a well pump. It can supply water at higher pressure than the tank, but only as long as the amount it can flow isn't exceeded.

Hope that makes sense.

Yeah, it does. Accidentally grounding the circuit activates the electrical flow, much like when my dumbass German Shepherd bites the garden hose and water starts pissing out of the bite hole.

Correct me if I'm wrong on this....in the diagram as I drew it....the voltmeter, since it's grounded, would activate the flow and this would cause the battery to eventually drain, yes?

 

[Mattax]

Yes. I think it would be very slow since its such high resistance in the meter.

 

[FLynes]

BTW. This probably one reason why charging systems got ammeters. A voltmeter can not reveal if current is flowing to the battery. It will show if the alternator is not working (voltage will be battery voltage 12ish) or can't keep up with demand (between 12 and 14). But when showing 14 volts, we can only assume the battery is charging properly.

And it would make perfect sense to keep the ammeter but for one thing....since it is a motorhome, I do want to upgrade the alternator. There were four alternators available on the B-Vans, 41 Amp. (Red Tag), 50 Amp. (Green Tag) and two different 60 Amp. (Blue & Natural Tags)....no idea what the difference is between the two 60 Amp. models. With the appliances that operate on 12V, the alternator needs to be powerful enough to keep the Coach/House battery charged, while driving. Everything I've read says that, if I upgrade to a 90A or higher alternator, I'm probably going to fry the bulkhead connectors and the ammeter, as it is currently configured. This is why I want to reconfigure the electrical system and go to a voltmeter.

 

[FLynes]

Quick addendum....my Service Manual only lists regulator P/N 3438150...mine is 3755850 (no mention of it in the Service Manual), with a date code of 235 (2-6JUN75), so I know it's the original. My regulator, when I Googled it, is for 100 Amp alternators, so apparently the Warren Plant built these chassis cabs with the understanding that they needed heavy duty electrical systems, but I seriously doubt they installed the Leece-Neville 100 Amp alternators. IIRC, the Leece-Neville units had the battery post, a smaller round ground post and only one field spade connector. My wiring harness is not setup that way, which tells me that it had a regular Mopar alternator, but I wonder if the wiring and ammeter are actually engineered to handle the extra amperage, without melting down. If they are, I can just buy a regular Mopar alternator rated for 100 Amps and swap it in.

 

[Mattax]

Everything I've read says that, if I upgrade to a 90A or higher alternator, I'm probably going to fry the bulkhead connectors and the ammeter, as it is currently configured. This is why I want to reconfigure the electrical system and go to a voltmeter.

I can't answer the questions about what came on it, and the differences.
A higher output alternator will not increase the load on anything. It's the equipement that creates the load. The ignition, headlights, wipers, are only going to draw what they need. Or more precisely, the current flow through them will be limited by the internal resistance and the voltage across them. The resistance is fixed and the voltage is regulated.
Lets take a pair of headlights, nominally rated 60/55 Watts. At 12 Volts, 9 amps will pass through them. With the alternator running and regulated to 14 Volts, it could be 11 amps. Only 11 amps will flow through those wires regardless of the capacity of the alternator.

There is one item that doesn't have a fixed resistance, the battery. If the battery is low, it will suck more current at any given voltage. So this is the one circuit a higher output alternator potentially could fry connectors, and even the fusible link or at least weaken it.
Here's a low battery in my wagoneer, using a charger with manual regulation. Initially it draws over 30 amps at 14.2 Volts.

Well I don't want that because that makes a hot battery which in turn makes it harder to accept a charge. It also can cook off the acid - very bad in an AGM battery.
So I reduce the voltage and current.

But 15 minutes later, its charging at less than 5 amps even though the voltage is again reset for 14.5 V

With an alternator and the voltage regulated some other strategies need to be used. That's why I asked about the regulation of the coach battery charging and was speculating about the battery to battery connector with the smaller section wire.

The maximum power an alternator can provide varies with rpm. They can be pretty poor performers at low rpm but quickly do better as rpms increase. When testing for maximum power, the regulated voltage also makes a difference. So the power ratings are a bit of game. It seems that most companies give alternator their ratings based on something close to maximum rpm and its a crapshoot as to what voltage.

(rpm is alternator rpm)

Another real life example. A couple years ago I left the parking lights on after driving in a patchy fog. After work, I got a jump start. The ammeter showed roughly 10 amps charging. As soon as I started driving, the charge rate went up. Doing over 35 mph it was a bit over 30 amps. Way too much for my comfort on a 20 - 30 minute drive. So I put into N and let it idle on all downslopes, drove closer to 25 mph, and turned on the headlights to divert a portion of the current. My headlights are on relays, so this also reduced current through the alternator wire and connections into the car. All these tricks worked because the alternator's power was maxed out at lower rpms. When I got back to our base camp, the battery was hot. We didn't have a charger. The next morning, it was cooled off, started it and basically used the same techniques. Having had a chance to cool and get somewhat recharged, after about a half hour it was only drawing a few amps regardless of speed I was driving.

Point here is not that a lower rated alternator is prefered. The above is an unusual situation. Rather this is an illustration of how the alternator output and battery charging relate.
In fact, under normal conditions, it is most desirable for an alternator to have enough power at idle speed to run everything at 14 Volts.
If it can't, then the battery must provide some. Then as rpms rise, the alternator has to recharge the battery. If this happens for hours on end, like stuck in traffic with A/C and lights on in 90 degree weather, the battery gets more and more drained, and when the car finally does move, the charging rate is high. The result is constant load, some of it high, on the fusible link, connectors etc in the charging circuit.

In the 60s, this was probably not in the design scenario. Rather the only big drain would be starting, and then after starting the engine would be on fast idle, easily taking care of the normal recharge from a cold start.

I suppose its possible your camper's design took advantage of the alternator's lower output at idle speed to somewhat recharge the battery, but would need to find somebody who really knew. It seems kindof crude and uncertain, as an owner might start it up and then go hit the freeway.

One more item. While higher alternator rating is often better, sometimes this is achieved at the expense of low rpm performance. Example from the Remy-Delco catalog for a GM alternator, sorry generator. LOL. GM never stopped calling them generators.

 

[FLynes]

I can't answer the questions about what came on it, and the differences.

I can, but only to a certain degree. Unfortunately, the MB300 is often overlooked in the Mopar Service Manual....the '74-'77 Parts Catalog is a better, but the people selling them online are very proud of them.

A higher output alternator will not increase the load on anything. It's the equipement that creates the load. The ignition, headlights, wipers, are only going to draw what they need. Or more precisely, the current flow through them will be limited by the internal resistance and the voltage across them. The resistance is fixed and the voltage is regulated.
Lets take a pair of headlights, nominally rated 60/55 Watts. At 12 Volts, 9 amps will pass through them. With the alternator running and regulated to 14 Volts, it could be 11 amps. Only 11 amps will flow through those wires regardless of the capacity of the alternator.

But having the correct Voltage Regulator matched to the alternator does play into whether you fry your electrical system, right? At least, this is what I've read, and this is where I get a bit confused, because the alternator is supposed to put out consistent voltage based on its RPM, so why would there be different Voltage Regulators? Do they also play a role in regulating amperage?

There is one item that doesn't have a fixed resistance, the battery. If the battery is low, it will suck more current at any given voltage. So this is the one circuit a higher output alternator potentially could fry connectors, and even the fusible link or at least weaken it....

With an alternator and the voltage regulated some other strategies need to be used. That's why I asked about the regulation of the coach battery charging and was speculating about the battery to battery connector with the smaller section wire.

And this is my concern, given that for 43 years it has had that Battery Isolator Charging Solenoid. As it stands, the Coach/House batteries (I actually have room for two) rely on the alternator to charge them and, since my electrical system is stock, I would need to continuously monitor their health, so that the chassis cab system isn't working overtime to maintain them, when I'm on the road.

Point here is not that a lower rated alternator is prefered. The above is an unusual situation. Rather this is an illustration of how the alternator output and battery charging relate.
In fact, under normal conditions, it is most desirable for an alternator to have enough power at idle speed to run everything at 14 Volts.
If it can't, then the battery must provide some. Then as rpms rise, the alternator has to recharge the battery. If this happens for hours on end, like stuck in traffic with A/C and lights on in 90 degree weather, the battery gets more and more drained, and when the car finally does move, the charging rate is high. The result is constant load, some of it high, on the fusible link, connectors etc in the charging circuit.
In the 60s, this was probably not in the design scenario. Rather the only big drain would be starting, and then after starting the engine would be on fast idle, easily taking care of the normal recharge from a cold start.

So this is where thicker gauge wire relaxes the stress that the electrical system experiences. At a minimum, even if I don't change the existing wiring schematic on my chassis cab, it will definitely benefit from thicker gauge wires. I know my first plan of attack will be thicker and added ground wires in the engine compartment. The guys on the Jeep Forum who preach thicker gauge and added ground wires under the hood. I figure if it's a good idea for the old AMC, it's probably a good idea for the old Dodge too.

 

[toolmanmike]

You just answered your question as to why your alternator is constantly charging, The coach battery (or batteries) are shot. If your motorhome doesn't have a battery isolator you need to get one. I had chassis/coach batteries in 4 different tool trucks in 28 years of the tool business. @ trucks had isolators and 2 used a constant duty relay to charge the coach batteries. The isolator separates the 2 electrical systems and only charges the batteries that need the charge. Your engine start/chassis battery doesn't need much charge unless you are using the lights, heater, wipers, etc. If you use the camper for any length of time those batteries will need charged. With no isolator your system will charge one set and overcharge the other set. I had many battery and alternator failures because of overcharging in the trucks without a isolator.[/QUOTE] That bad coach battery will cause the system to overwork.

 

[67Dart273]

You just answered your question as to why your alternator is constantly charging, The coach battery (or batteries) are shot. If your motorhome doesn't have a battery isolator you need to get one. I had chassis/coach batteries in 4 different tool trucks in 28 years of the tool business. @ trucks had isolators and 2 used a constant duty relay to charge the coach batteries. The isolator separates the 2 electrical systems and only charges the batteries that need the charge. Your engine start/chassis battery doesn't need much charge unless you are using the lights, heater, wipers, etc. If you use the camper for any length of time those batteries will need charged. With no isolator your system will charge one set and overcharge the other set. I had many battery and alternator failures because of overcharging in the trucks without a isolator.

Sorry but MOST of this is not true. A "battery isolator" is nothing more than a pair of diodes. They do not magically figure out which batteries "only need charged." IN FACT back in my parts days there were a couple of VERY DANGEROUS failures because of isolators. The diode supplying the main battery runs hotter because that battery sees more draw and use. So that diode tends to fail, and it sets up the following condition:

If the main diode fails, the main battery starts to drop and that is where the regulator sensing is connected. So the regulator ramps up charging voltage to a higher and higher level, trying to bring up the main battery. Since there is no longer a closed loop so to speak, that can get fairly high. Meanwhile, the poor secondary battery is over there bubbling furiously with overcharge

In my opinion you are WAY safer and better off with a constant duty solenoid. It ties the batteries together and tries to equalize their voltage, and can also be used as a "jumper" if you leave the lights on eg and run the main down. It can fail, but will leave the alternator properly connected to the main

There is no doubt that a bad battery such as one with a low/ dead cell can screw things up

 

[FLynes]

You just answered your question as to why your alternator is constantly charging, The coach battery (or batteries) are shot. If your motorhome doesn't have a battery isolator you need to get one. I had chassis/coach batteries in 4 different tool trucks in 28 years of the tool business. @ trucks had isolators and 2 used a constant duty relay to charge the coach batteries. The isolator separates the 2 electrical systems and only charges the batteries that need the charge. Your engine start/chassis battery doesn't need much charge unless you are using the lights, heater, wipers, etc. If you use the camper for any length of time those batteries will need charged. With no isolator your system will charge one set and overcharge the other set. I had many battery and alternator failures because of overcharging in the trucks without a isolator. That bad coach battery will cause the system to overwork.

Yeah, I tend to think outloud, to make sure I'm on the right track. The Chassis Cab does indeed have an isolator....it's in one of the pics I posted. I tend to keep what the original engineers designed....I still run the original Prestolite ignition system on my CJ-5 and have had ZERO issues. If you talk to a good number of the AMC/Jeep guys, they'll refer to that system as Prestocrap.

In this case, though, my train of thought is that Mother Mopar could only anticipate so much, when they were building the MB chassis cabs....the motorhome manufacturers are the ones who throw the monkey wrench into the equation, when they installed their appliances/systems, and I want to make sure that my entire electrical system is up to the task of taking care of, not only the chassis cab components, but that it also has the ability to not falter, when it's charging the Coach/House batteries, while we're on the road. Since our fridge is 3-way, I prefer to run it on 12V, while we're driving, so that we don't run into any problems when we refuel. I've heard of fires starting, when RV'ers pull into service stations and their fridges are running on propane.

 

[Mattax]

@toolmanmike He posted a picture of the solenoid on the previous. Maybe you can take a look since you know more about how they work with recharging. Is that connector between the batteries purposely restrictive?

The rest of the wiring looks very robust. As long as the metal connecting terminals are equal to wiring and in good shape, its probably plenty good. There's no need for a 4 gage wire if a 10 gage wire causes no resistance at maximum current. There's a point of dimishing returns. heavy cables are less flexible and heavy. That's the balance that needs to be found.

But having the correct Voltage Regulator matched to the alternator does play into whether you fry your electrical system, right? At least, this is what I've read, and this is where I get a bit confused, because the alternator is supposed to put out consistent voltage based on its RPM, so why would there be different Voltage Regulators? Do they also play a role in regulating amperage?

Alternators are not self regulating. If power is provided to the alternator's spinning windings (rotor) without a regulator, voltage will go up with rpm. Current flowing out is zero until something is attached. If we attach a basic ignition, 1 or 2 amps will flow out. If we also connect the alternator's field, another two amps, headlights 10 more.

Batteries are a chemical reaction, so they can draw a lot if the alot of the electrons are on the opposite position, and draw little when they've all move back to the plates.

The dilema is how to monitor the health of the batteries. A voltmeter on the vehicle system doesn't reflect the health of any of the batteries. To know the condition of the battery, you can monitor its charge rate, or the battery alone can be given a known load and the amps or voltage checked. Preferably both, but either will give a reasonably good idea of condition.

 

[toolmanmike]

Sorry but MOST of this is not true. A "battery isolator" is nothing more than a pair of diodes. They do not magically figure out which batteries "only need charged." IN FACT back in my parts days there were a couple of VERY DANGEROUS failures because of isolators. The diode supplying the main battery runs hotter because that battery sees more draw and use. So that diode tends to fail, and it sets up the following condition:

If the main diode fails, the main battery starts to drop and that is where the regulator sensing is connected. So the regulator ramps up charging voltage to a higher and higher level, trying to bring up the main battery. Since there is no longer a closed loop so to speak, that can get fairly high. Meanwhile, the poor secondary battery is over there bubbling furiously with overcharge

In my opinion you are WAY safer and better off with a constant duty solenoid. It ties the batteries together and tries to equalize their voltage, and can also be used as a "jumper" if you leave the lights on eg and run the main down. It can fail, but will leave the alternator properly connected to the main

There is no doubt that a bad battery such as one with a low/ dead cell can screw things up

Well you're a smarter guy than me when it comes to this stuff but I know what worked for me. My last truck was a pain and I finally just hooked the trip wire to the relay on a toggle switch. I idled with the interior lights on and 2 heater fans on high all winter/8 hours a day. It was hard on batteries (especially the engine start batteries that didn't need charged) and alternators.

 

[Mattax]

I still run the original Prestolite ignition system on my CJ-5 and have had ZERO issues. If you talk to a good number of the AMC/Jeep guys, they'll refer to that system as Prestocrap.

Not quite as extreme on the SJ forums, but similar. So alot of guys were doing this 'TFI conversion' which left something like half of them stranded because they cut out the resistance wire and increased the coil voltage. The Duraspark isn't a bad a system and they would have been better off leaving it as it was. They didn't understand the later coil was used with a controller that regulated coil power like GM did with the HEI module.

 

[FLynes]

Sorry but MOST of this is not true. A "battery isolator" is nothing more than a pair of diodes. They do not magically figure out which batteries "only need charged." IN FACT back in my parts days there were a couple of VERY DANGEROUS failures because of isolators. The diode supplying the main battery runs hotter because that battery sees more draw and use. So that diode tends to fail, and it sets up the following condition:

If the main diode fails, the main battery starts to drop and that is where the regulator sensing is connected. So the regulator ramps up charging voltage to a higher and higher level, trying to bring up the main battery. Since there is no longer a closed loop so to speak, that can get fairly high. Meanwhile, the poor secondary battery is over there bubbling furiously with overcharge

In my opinion you are WAY safer and better off with a constant duty solenoid. It ties the batteries together and tries to equalize their voltage, and can also be used as a "jumper" if you leave the lights on eg and run the main down. It can fail, but will leave the alternator properly connected to the main

There is no doubt that a bad battery such as one with a low/ dead cell can screw things up

That isolator is a solenoid....its official name is "Battery Isolator Solenoid". The only thing I don't know is what amp rating my isolator solenoid is. I think it's 90A but I wouldn't bet a nut on it. And you are correct, the solenoid is, for lack of a better word, "dumb". With 12V switched power, the solenoid allows the alternator to charge the batteries, but there is no way to smartly charge each individual Coach/House battery, without installing separate "smart" chargers, and I just don't have the room for it, nor do I think it's really necessary. Truth be told, running a 10ga. wire 18ft to the Coach/House battery compartment isn't very efficient....IIRC, I should probably have at least a 1/0 wire for the dual battery setup, to be effective, but Monaco went with the 10ga. most likely because of cost and because the original setup only had one Coach/House battery.....my original battery housing was shot, so I went to the original manufacturer and they only have a dual battery housing now. I think the last time I priced wire, it came out to +/- $150.

 

[FLynes]

Not quite as extreme on the SJ forums, but similar. So alot of guys were doing this 'TFI conversion' which left something like half of them stranded because they cut out the resistance wire and increased the coil voltage. The Duraspark isn't a bad a system and they would have been better off leaving it as it was. They didn't understand the later coil was used with a controller that regulated coil power like GM did with the HEI module.

Yep, and the guy who takes credit for inventing that TFI conversion goes by the screen name of JeepHammer. Very long-winded guy. His heart is in the right place, but his info is just outdated and some of it is dead wrong.

 

[Mattax]

and alternators.

I suppose when an alternator is running close to 100% duty cycle its going to be getting and staying rather hot. This is probably one of the differences in alternators made for these types of uses. Better cooling and heavier insulation and windings.

 

[toolmanmike]

I suppose when an alternator is running close to 100% duty cycle its going to be getting and staying rather hot. This is probably one of the differences in alternators made for these types of uses. Better cooling and heavier insulation and windings.

I had a kick up solenoid for the a/c that really helped.

 

[Mattax]

Yep, and the guy who takes credit for that TFI conversion goes by the screen name of JeepHammer. Very long-winded guy. His heart is in the right place, but his info is just outdated and some of it is dead wrong.

OT, but since we're talking about it, there is guy on the carburator forum who kept that coil when going the other way with his Mustang. He got rid of the fuel injection and EEC IV, so he needed a simple ignition system controller. I pestered him to post the details, which he did.
Thread here if your interested: More on E-core coils, TFI and Duraspark.