over chargeing/blowing fuse?

[mopar56]

Ok so my sons 70 Duster we resurrected last year has been running well since we got her on the road last June, during the resurrection process we performed the " Mad " bypass, we have done this procedure on his last Duster to, however instead of using fuseable links we used marine 10 gauge ato fuse holders with a 40 amp fuse in one and I think a 25 amp in the other, we only used different fuse sizes because the procedure called for different gauge fuesable links, any way just lately the alternator stopped charging which we diagnosed to a blown 40a fuse we replaced it and all was good, we checked the voltage at the battery and watched the voltage increase but instead of leveling out at 14.2 it kept climbing and finally blew the fuse again, we checked for grounded hot wire but could see nothing. I suspected a bad voltage regulator so replaced it with what I believe is a good used one I had in my parts cabinet but got the same result, it charges at idle but as you increase rpms the voltage increases at the battery on the meter and somewhere between 14.7 -15 v it blows the fuse, any ideas? BTW the alternator was professionally rebuilt last June to and has very little mileage as the car is stored in the winter.

 

[Dana67Dart]

Im not sure what the MAD bypass is but it sounds like you are bypassing the connectors through the firewall and amp meter gauge in dash.

get a clamp on amp meter and see how much draw the battery is taking, measure on the battery negative to block wire.

have the battery checked at autoparts store.

depending on the regulator 14.7 is not wrong my 67 runs 13.8ish but I have always heard 13.7 to 14.7 is normal.

your car might be drawing more than 40 amps between charging battery, accessories, lights etc. use clamp on amp meter on the fuse wire as well.

If I recall correctly a fusible link is like a slow blow fuse in that it can take a lot more than its rated current for a short period of time while a standard fuse will not.

I don't recall the details but there is a wire from the regulator to the alt that controls the output from the alt. it sort of modulates the field if I recall correctly. could be something there? In a testing procedure it call on doing something with that wire to the alt and watching the output voltage from the alternator climb to 16 17 volts then ending the test . if it doesn't climb alternator is bad ( don't think alternator is your problem).

Lastly. can you temporarily return things to stock and check voltages and current at various points?

that's all I got

 

[67Dart273]

I try to "loosely" group charging problems into (no particular order)

The major components, battery, alternator, regulator

The field wiring

The charge (output) wiring

FIRST thing to do is find out if the regulator "has" control. To do that is simple, simply run the engine, watch battery voltage with the regulator unplugged. If it charges at all or too much, the field brush hooked to the green wire is grounding, causing a "full charge" condition. This could be right at / in the alternator, or the green wire itself may have shorted/ melted to ground

If that test is OK, make ABSOLUTELY certain the regulator is grounded. Scrape around the mounting bolts, use star lock washers, and make sure the bolts tighten (are not stripped)

Next, check for voltage drop to the VR. To do that, access the closest electrical point to the VR IGN terminal (blue wire on the VR connector) This might be the ballast resistor. Check with your meter, key "in run" with engine stopped for the highest reading. Leave all wiring connected, don't pull connectors off

Now with one probe on the ballast resistor "key" side of the resistor, put the other probe on battery PLUS. You are hoping for a very low reading, the lower the better. More than say, .3-.4V (3/10 of one volt) means you need to be looking. Whatever that reading is there, is added to the nominal 14V charging voltage

 

[mopar56]

ok thank you both I do have a meter with am meter clamp and all the test mentioned are easy to do, I will get back to this asap but might be Friday and check back, thanks

 

[694spd]

Make sure your clamp on amp meter can read DC amps. A lot of them are for AC amps only.

 

[toolmanmike]

If that test is OK, make ABSOLUTELY certain the regulator is grounded. Scrape around the mounting bolts, use star lock washers, and make sure the bolts tighten (are not stripped)

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This.

 

[Garry in AZ]

Agreed on double checking the regulator ground. I learned that one the hard way myself.

 

[mopar56]

Ok so I finally got back to this problem tonight first of all something dana67 said was maybe the battery was charging at more than 40 amps and that's why it popped the fuse. That got me to thinking the was sitting for a bit and the battery was week and we boosted it with a booster pack my son did charge it but I know from talking g to my Interstate battery rep at work that it can take several days if charging at 10 amps to properly bring a battery back soooo....is it possible that the 55amp alternator was charging 40 amps and popped the fuse? Now that being said I did all the test tonight I unplugged the regulator and it wasn't charging so ok I check amperage with a clamp on meter but inconclusive I'm not 100% it reads DC amps it doesn't say and a cheaper meter I have a better on at work I should bring home also I ran the meter between ballasts resistor and positive battery I got 1 volt I know 67dart said it should be less than 1/2 volt but I'm not convinced there is a problem there we are only talking 1/2 volt difference? Lastly I ran a second ground to the regulator right now it doesn't seem to be popping the fuse maybe cause the battery is charged more? The kid was going to read test it tonight also I was thinking of upping the fuse to 50 amp my alternator is only 55 so that should be better?

 

[mopar56]

So road test completed no blown fuse so either battery was charging too hard or maybe extra ground helped? Still think I might up the 40 amp fuse to 50. Thanks guys once again a very helpful bunch here!

 

[Dana67Dart]

Sounds like you are on to a final solution. Regulator ground, and fuse, you might stay with 40 amps but get slow blow fuse?

I have a 30 year old sears clamp-on amp meter. I did not think it could read DC amps but sure enough I put it on the + charging cable and it worked. After sitting for a week or 2 and starting the engine it was putting 10 amps onto the battery. After driving for an hour or so the charging curent was down to 5 amps or so.
Also all tests are with no accessory or lights on.

 

[67Dart273]

You likely have found the problem. Charging fuse MUST be large enough......along with wiring!!! To handle the max of the alternator.