Non Mopar Battery Isolator question

[equium]

I have a service truck with a pressure washer in the bed. It has it's own 20hp honda engine with electric start. The company that installed the equipment put the battery isolator back near the honda's battery. I'm getting tremendous voltage drops. I'm attaching a crude drawing. I'm not sure if I should move the isolator closer to the battery, or just jumper the truck battery off the alternator to decrease the distance. Thanks for reading.

 

[67Dart273]

To actually answer your question, yes, the isolator belongs near the main battery / alternator, and must be wired with large enough wire, depending on alternator capacity. Even a relatively small "one wire" alternator (eg) needs LARGE wire, 40-60A needs no 6 or so. This is because a "one wire" has the "sensing" typically right at the alternator. In any case, use adequate wire gauge.



I DO NOT LIKE ISOLATORS!!!! And here is why

An isolator is nothing more than two diodes hooked in such a way as to charge both yet isolate both batteries. "As long as they work" then "so far so good."

In a previous life I've seen a number of these fail, TWO of which were in marine installations, and both of those were very very dangerous

Here is the failure mode:

Typically the MAIN battery diode fails. This might be because it is used more heavily. Now, you have a main battery going dead, and the voltage regulator "thinks" it needs to ramp up voltage because the sense line is on the main.

So the aux. battery is now running at high overvoltage, overcharges, and pukes acid and explosive hydrogen

What to do instead?

Use a "continuous duty" solenoid. This is a solenoid which resembles a Ford starter relay/ solenoid, except the coil is designed for 100% use, unlike starter solenoids.

They typically have two small and two large terminals.

Hook the alternator back up to the main battery.

Connect one large terminal of the solenoid to a main battery connection, and run a whatever-gauge-wire you think is large enough back to the aux. battery from the remaining large solenoid terminal.

Now simply ground one of the small terminals, and run the remaining to an "ignition run" connection.

==========================================

The other "great" thing about a solenoid over an isolator is that if you are running fairly large loads off the second battery, AND you have the system adequately wired, the main part of the system, both the battery and alternator, can help "boost" the load on the second battery when the vehicle is running (solenoid energized)

 

[equium]

67Dart273, I like your solution. So basically, the Isolator and continuous duty solenoid do the same thing? I don't like the fact that my main battery is only getting 12.8v while running. I'm going to have a few accessories running and I don't think 12.8v will keep up.
Thanks again. Off to Amazon to order a solenoid

 

[67Dart273]

Yes, basically same job. A little more wiring, if you would have started from scratch, just about a trade off. How large is the wire to the aux? You might do well to parallel the two that are there now, and use them "as one" to the rear.

 

[TrailBeast]

Yes, basically same job. A little more wiring, if you would have started from scratch, just about a trade off. How large is the wire to the aux? You might do well to parallel the two that are there now, and use them "as one" to the rear.

I used to wire these systems for RV's some time ago (for charging toy hauler batteries while driving), and I totally agree with Del's solution.
Perfect, as usual.

I'll bet as he also says, the wire running back there for the rear battery is very likely too small to carry enough amps to do the job.
Of course this may not be the problem in your case, but it sure is a common mistake.

If removing the isolator doesn't help the truck battery voltage problem then you'll need to find out where it's getting lost in the truck system itself. (it's charging the washer battery right?)

 

[equium]

I used to wire these systems for RV's some time ago (for charging toy hauler batteries while driving), and I totally agree with Del's solution.
Perfect, as usual.

I'll bet as he also says, the wire running back there for the rear battery is very likely too small to carry enough amps to do the job.
Of course this may not be the problem in your case, but it sure is a common mistake.

If removing the isolator doesn't help the truck battery voltage problem then you'll need to find out where it's getting lost in the truck system itself. (it's charging the washer battery right?)

Yes, my alternator charges the washer battery. I've ordered the solenoid and will double the wires since they're already there. The truck is an '05 Silverado that I just learned has parasitic battery drain issues. Yet another thing I might be addressing soon.

 

[jumpshowhigh]

I have a buddy that has an isolator from Perfect Switch which is pretty slick. Doesn't look like normal isolators and it definitely isn't a starter solenoid.

 

[67Dart273]

I have a buddy that has an isolator from Perfect Switch which is pretty slick. Doesn't look like normal isolators and it definitely isn't a starter solenoid.

I would be SO nice if you guys would post a LINK to what you are referring to.

This thing I assume?

http://www.perfectswitch.com/orderingbuy/

"At only" just over 300 bucks!!!! for just the device, a solenoid looks pretty good to me. This device is switched (triggered) high power mosfet devices, and while "possibly elegant" certainly ain't cheap.

 

[crackedback]

Voltage drop is a function of the wire not being sized properly or really crappy connection/connectors for your amp load.

Those high dollar solutions are funny sometimes. I had a customer with a Road lamp equipped 71 Cuda. Had an issue with the factory relay that turns off the roadlamps when high beams were activated. Factory relay = ~$200 A Bosch relay/connector.... $15 It works same as the factory envisioned.

 

[equium]

Voltage drop is a function of the wire not being sized properly or really crappy connection/connectors for your amp load.

Those high dollar solutions are funny sometimes. I had a customer with a Road lamp equipped 71 Cuda. Had an issue with the factory relay that turns off the roadlamps when high beams were activated. Factory relay = ~$200 A Bosch relay/connector.... $15 It works same as the factory envisioned.

I did a bit more research and the consensus is that isolators should be installed as close to the alternator as possible. I agree that wire size also plays a factor.

 

[67Dart273]

The other thing I eluded to above, is that "conventional" diode isolators have "so much" voltage drop built in. This is because they use big power diodes, which depending on current have a nominal drop of somewhere around .5--.7V. So if your wiring is meager, this adds up fast

 

[ntsqd]

There used to be two quality options in Voltage Sensing Relays. Unfortunately Blue Seas bought BEP Marine and has gone all Mallory on them. Can't get the product from previous vendors, marine outlets are now the only place that I can find these things.

Premise is that right after a start that the starting battery should get fully re-charged as a priority. then the Aux battery bank can be brought up to full charge. The relay monitors the voltage on one or both of it's terminals. When the one or either reaches a full state of charge voltage the relay closes and connects the other battery to the charging source. I see these as one step better than a constant duty solenoid because there is a little management of charge happening rather than just working the alternator to death.

http://www.westmarine.com/buy/blue-sea-systems--mini-automatic-charging-relay--14152557

 

[equium]

The original wire from the alternator in this truck was only about 1' long. It attached to a factory tap in the cable from the POS battery terminal and the starter. With that being said, what size wire should I use to replace it with?
Here is what I have on hand:
1/0 gauge wire
9 gauge wire
5 gauge wire
(The 9 and 5 gauge wire is from a stereo amplifier install kit I scored at a thrift store for 3 bucks. I just wanted the wire.)
thanks

 

[Rustedwrench]

My question is why the Honda engine is tied to the vehicle charging system at all. If the Honda is a 20hp GX series with electric start I would expect it to have a 20 amp charging system. Maybe it depends on the engine. And what else is connected to the Honda.

If it was mine I would disconnect the Honda from the vehicle system. I would test the Honda battery and then the charging voltage with the engine running. When that is sorted out I would address why the vehicle is only charging at 12.8 volts.

 

[equium]

My question is why the Honda engine is tied to the vehicle charging system at all. If the Honda is a 20hp GX series with electric start I would expect it to have a 20 amp charging system. Maybe it depends on the engine. And what else is connected to the Honda.

If it was mine I would disconnect the Honda from the vehicle system. I would test the Honda battery and then the charging voltage with the engine running. When that is sorted out I would address why the vehicle is only charging at 12.8 volts.

I didn't think about that. that's a good point. The honda should have its own charging system. I'm going to give that a try and see how much it's putting out. I'm working with equipment installed by someone else. Thanks for the idea.