Smoke at low side (24v) battery terminal when starting - 38v at high side! (1 Viewer)

[BreckenridgeCruiser]

Hey all,

So I have been having trouble starting for a while now and after cleaning the solenoid on the starter I put the starter back in. When I tried to start it I had smoke coming from my low side + terminal and what looked like welding slag from the terminal possibly melting a bit.

I tested the batteries and the both show 12.5 and 12.7 but when I test between the top side + terminal and the block for ground I get 38V with the low side ground to chassis disconnected. When I connect the low side ground I get 25.5V

What the heck is going on? Would a bad starter motor cause this issue? I have a spare starter but want to make sure I check the electrical system before swapping it in. Could it be a bad battery?

Anyone have ideas of where I can start testing to figure out what is going wrong where?

Thanks!

 

[BreckenridgeCruiser]

Here are pics of the fried terminal and the good one for comparison...

Could a bad starter motor that is not turning cause this?

 

[gerg]

Turning over really slow? I wonder if you starter is sucking the amps if it could heat you post up enough to melt it?

Edit.
Sorry I didn't read your post correctly....
That is funky. I haven't a clue sorry man. Sheesh.

 

[db3]

A loose or very badly corroded connection would cause the damage shown, but I would also suspect excessive current draw from the starter as well. As for your voltage readings, are you using a high impedance digital voltmeter? If so, disconnecting the ground lead from the battery will result in erroneous voltages being induced on the positive lead if still connected to the battery positive terminal. This can be a result of local RF or fluorescent lights. In effect, your voltmeter lead and truck wiring acts like a giant antenna.

 

[BreckenridgeCruiser]

Turning over really slow? I wonder if you starter is sucking the amps if it could heat you post up enough to melt it?

Yes turning over really slowly. I was thinking the same way you, just confused on why the low side positive would fry like that.

A loose or very badly corroded connection would cause the damage shown, but I would also suspect excessive current draw from the starter as well. As for your voltage readings, are you using a high impedance digital voltmeter? If so, disconnecting the ground lead from the battery will result in erroneous voltages being induced on the positive lead if still connected to the battery positive terminal. This can be a result of local RF or fluorescent lights. In effect, your voltmeter lead and truck wiring acts like a giant antenna.

All of the wiring to the batteries are just a year old and were really well sealed from corrosion. Batteries are AGM so no corrosion on the terminals.

I am using a fluke 117. Very interesting about it becoming a receiver. I am still new to a lot of the electrical side even though I did a lot of the wiring on my truck. I get circuits but things like what you are describing still are still a bit out of reach.

 

[VX 12HT]

actually mine did this tried to catch on fire when my starter motor let go and would not disengage that was the battery post that melted..

 

[BreckenridgeCruiser]

Looks like I'm swapping starters... And then taking my batteries back to Sears!

 

[db3]

just confused on why the low side positive would fry like that.

In a 24 volt series circuit like yours, the same current flows though all wires and connections at both batteries. The most likely explanation is the low side positive terminal, for some unknown reason, had a slightly higher resistance. This could have been the result of a bad connection due to thermal cycling, vibration, or even a bad battery post. With a starter drawing excessive current, this resistance heated the terminal, resulting in even higher resistance, which resulted in more heat, etc. Eventually battery post started to melt, causing the resultant arc splatter. What I'm still puzzled about is the 38 volt reading. My assumption was you were using an inexpensive meter, which is not the case. After thinking about it, the situation I described usually involved AC readings in an industrial setting, with lots of RF and induced voltages from high power equipment. Over the years I have experienced occasional problems with Fluke meters, (I've owed many and still have four, IIRC) but usually interference problems on the DC ranges resulted in the meter behaving erratically, i.e. flashing, and at times not displaying anything. Further, newer meters have much better shielding and circuits to avoid these problems, so I'll have to give your situation more thought.

 

[BreckenridgeCruiser]

So I swapped in a tested good starter and same behavior.... Looks like the starter is drawing normal amps but it is just not getting enough juice to turn over the engine. when I turned the key it groans like I have low batteries and then I get smoke from that terminal. Again when this behavior was starting the truck would weakly start, but run fine once it turned enough to start (surprisingly low revs to get this thing to fire!).

I am starting to look at the batteries as the weak link. I have two AGM Sears Platinum batteries that are around two years old from similar batch and close mfg dates. @beno told me that he does not think that those do well in 24v environments. I am not trying to start an opinion war on batteries, but I wonder if they are the culprit.

I do have a few other questions in case it is not the batteries:
- Would bad ground from the starter to the frame cause this behavior?
- What about bad ground from the frame/body to the negative terminal in the series batteries (true ground).

Thanks! Any ideas are good one!

 

[BreckenridgeCruiser]

Oh, and I'll retest again on the 38v... I'll let you know if I get that reading again... Remember that was when I disconnected the low side battery ground wire and then put my red probe from the high side battery + terminal and the black probe on the engine head cover. I am hoping I misread something somewhere.

 

[db3]

The fact you are getting smoke from that same battery terminal would lead me to believe you have a bad post, possibly the internal connection. You need to find out what's causing the smoke and repair it. Next, clean all connections, as any bad connection will affect your starter voltage. Use your meter to check the voltage at the starter as compared to battery terminal voltage (hopefully not less than 18-20 volts) while cranking. The difference will be the circuit losses, which you want to minimize. Be sure to carefully inspect the wires and terminals, as poor crimps or soldering can cause issues. Replace anything that shows corrosion, broken, or frayed wires. Next I would invest in a good battery load tester, something similar to this one: Amazon.com: OTC 3180 100 Amp Battery Load Tester: Automotive. First fully charge each battery, wait a few minutes and load test each separately. The readings should be very close; one weak battery will drag down the other. AGM batteries sometimes develop high internal resistance, even when relatively new. This could be why @beno might think they don't do well in a 24 volt, series connected system. I'm very interested in whether you can duplicate the 38 volt reading. Once the negative from the low side battery is disconnected, the voltage can only be from some outside source, either real or induced.

 

[BreckenridgeCruiser]

Been raining here pretty hard so no news yet on the voltage readings. It is supposed to stop soon and I will be testing everything both in and out of the truck. Watch this space....

 

[Bob Richards]

Intently watching on the side to see the outcome

 

[BreckenridgeCruiser]

Okay... Finally got back to this...

So, the batteries tested fine and the only thing I can think of is that my ground cable at the starter is not handling the amperage. I will be having a oversized ground wire made and will also clean and re-secure the ground to the batteries.

I will let you know how it goes.