HMMWV Battery Polarity Keeps Reversing?

[TOBASH]

Either your batteries are in parallel or your generator is fried.

Might I suggest posting a picture of your battery setup AND might I suggest investing in a solar type battery tender.

AFAIK, your generator is suspect. Also, if you are running any 12V off of only 1 battery, then you are frying that one battery. You need to return to a factory setup.

When you replace batteries, you need to replace in pairs, especially after a weird situation like this. I also swap batteries every month from front to back, so no one battery gets over-charged in the series hookup.

If it is not one of those things, then find a shamen to remove the voodoo hex and curse.

Electrical issues are torture... I wish you well.

Best,

T

 

[JLAINC]

https://www.batterystuff.com/blog/battery-myth-can-a-battery-reverse-polarity.html

The first option in this article cannot be the case, so it must have something to do with number 2. Here is what he says about #2:

"

The second possibility is reversing polarity after the activation process. This is also rare, as it requires a sequence of errors to be present after the installation of the battery. The only way for this to happen would be to completely discharge the battery, either by leaving the key on, or by an unnoticed dead short that completely dissipated the charge over a few days. After that happened it would appear to be a dead battery.

Remember, a completely discharged battery is nothing more than an empty vessel. In order to gain a negative charge, it would then necessitate being hooked up backwards, and charged that way. So the real question here is: how can a battery reverse polarity after it has been installed? That same previously discharged battery would then be vulnerable to reverse charging, either by connecting the battery charger backwards, or by a charging system that reversed polarity (very rare, but still possible)."
​

So, there MUST be a dead short somewhere that is drawing on the back battery, but the vehicle has NOT been cranked for more than a month, which means that it has NOT be charged by the 60-Amp generator. The only thing I can think of is that the FRONT battery must be charging the back battery once it is completely drained. Both 12V batteries only registered around 4.5-Volts, but the rear battery was actually -4.5 because the polarity is now reversed.

Has ANYONE ever experienced this on a 24-volt vehicle with 2 12-volt batteries run in series?

 

[JLAINC]

Either your batteries are in parallel or your generator is fried.
Might I suggest posting a picture of your battery setup AND might I suggest investing in a solar type battery tender.
AFAIK, your generator is suspect. Also, if you are running any 12V off of only 1 battery, then you are frying that one battery. You need to return to a factory setup.
T

It is running on a brand new generator now, and it did this the first time prior to the replacement.

Below is a pic of my setup. The top battery is the rear, and the bottom is the front:

 

[TOBASH]

You're running two different branded batteries and probably of differing cranking amps.

Optimally you should run 2 identical batteries of the same lot number.

Also I see unidentified wires meaning that you have unidentified current draws that might be killing your system.

I can tell you from my experience with my 24 Volt Land Cruiser Diesel, you need 2 identical batteries that you swap back and forth to maintain lifespan, and a solar charger will extend the life of batteries even further.

You may have swapped in a new regulator, but have you checked its output?

MHO, your mileage may vary.

Best,

T

 

[M1097A2NUT]

You need to remove all non-factory connections to your batteries for starters to eliminate them as the cause. Second you need to completely disconnect the battery terminals from both batteries. Third is to individually charge each battery. Fourth you need to use a quality multimetervto test voltage and polarity on each battery. If after this you find one or both batteries are suffering from reverse polarity then you need to replace them BOTH as a set. Then you can check the positive lead for continuity to ground. Firast with the ignition switch in the off position and if no continuity then turn the switch to run and retest. Do the continuity tests without the batteries connected.

 

[JLAINC]

Optimally you should run 2 identical batteries of the same lot number.
Also I see unidentified wires meaning that you have unidentified current draws that might be killing your system.
T

This issue has already killed 4 batteries at this point, so I cannot afford to spend $250 on another set of new batteries until I can identify and correct the issue causing the reversed polarity.

The unidentified wires are the positive and negative leading to the 24v-12v converter. The fuse to that was pulled during the month+ time when the polarity reversal happened this last time.

 

[TOBASH]

You need to use 2 identical batteries, no matter what.

You need to remove the non-factory wires, not just the fuse, as the wire may have a short circuit.

You need to remove batteries and then turn vehicle to the off position with the key removed. Then test for resistance and current leakage. If there is measurable current after the vehicle is in "OFF" mode with key removed, then you need to look for the short circuit.

Time consuming and frustrating.

You will get NOWHERE with two dissimilar batteries. FYI. Do what you will, but 2 dissimilar batteries will ALWAYS result in charging imbalances, with one surviving and the other getting killed.

MHO, your court now. Like Bogey once said... "You pays your money, you takes your choice".

I hope you find the issue.

T

 

[M1097A2NUT]

You need to use 2 identical batteries, no matter what.

You need to remove the non-factory wires, not just the fuse, as the wire may have a short circuit.

You need to remove batteries and then turn vehicle to the off position with the key removed. Then test for resistance and current leakage. If there is measurable current after the vehicle is in "OFF" mode with key removed, then you need to look for the short circuit.

Time consuming and frustrating.

You will get NOWHERE with two dissimilar batteries. FYI. Do what you will, but 2 dissimilar batteries will ALWAYS result in charging imbalances, with one surviving and the other getting killed.

MHO, your court now. Like Bogey once said... "You pays your money, you takes your choice".

I hope you find the issue.

T

This is excellent and nearly identical advice to what I gave you. This is what I have done as my career for over 20 years. I am more than willing to walk you through each and every procedure to solve your issue but only if you are willing to follow directions as that is the only way to properly diagnose what is wrong.

 

[JLAINC]

This is excellent and nearly identical advice to what I gave you. This is what I have done as my career for over 20 years. I am more than willing to walk you through each and every procedure to solve your issue but only if you are willing to follow directions as that is the only way to properly diagnose what is wrong.

10-4, will do... It will probably be a while before I will have the time to do this. Thanks!

 

[tennmogger]

The first option in this article cannot be the case, so it must have something to do with number 2. Here is what he says about #2:

"

The second possibility is reversing polarity after the activation process. This is also rare, as it requires a sequence of errors to be present after the installation of the battery. The only way for this to happen would be to completely discharge the battery, either by leaving the key on, or by an unnoticed dead short that completely dissipated the charge over a few days. After that happened it would appear to be a dead battery.

Remember, a completely discharged battery is nothing more than an empty vessel. In order to gain a negative charge, it would then necessitate being hooked up backwards, and charged that way. So the real question here is: how can a battery reverse polarity after it has been installed? That same previously discharged battery would then be vulnerable to reverse charging, either by connecting the battery charger backwards, or by a charging system that reversed polarity (very rare, but still possible)."
​

So, there MUST be a dead short somewhere that is drawing on the back battery, but the vehicle has NOT been cranked for more than a month, which means that it has NOT be charged by the 60-Amp generator. The only thing I can think of is that the FRONT battery must be charging the back battery once it is completely drained. Both 12V batteries only registered around 4.5-Volts, but the rear battery was actually -4.5 because the polarity is now reversed.

Has ANYONE ever experienced this on a 24-volt vehicle with 2 12-volt batteries run in series?

===


You can't take that number 2 scenario literally. That scenario was not based on seriesed batteries. In your case the problem seems straightforward and post after post has told you so: there is definitely parasitic drain on your 12v battery, the one that reverses, and, probably a parasitic drain on the 24v system too, for the reason stated below.

Once the 12v battery drains, it is in series with another 12v battery. If there is any parasitic drain on the 24 volt system to provide current flow then that will charge the 12v battery in reverse. Think about it: the "dead" lower battery is connected with it's positive to a negative of the next battery in series. The 12v battery is also hooked negative to ground. If there is parasitic current in the circuit, the positive of the upper battery flowss through the load to the negative of the lower battery. Just like a battery charger but of wrong polarity. That lower battery has been charging in reverse since the truck ran last time, for a month, didn't you say?

With mismatched batteries, when you return to start the truck and draw hundreds of amps through the system, there is serious danger of a battery exploding. There's no mystery, just electricity at work.

So how long does it take to run down a battery? Even if the batteries are new, which they apparently are not, a cranking/starting-type battery has a relatively low Ampere-Hour rating. Maybe they are 100 AH but probably less. This is not the same as CCA, Cold Cranking Amps.

In a month of 720 hours, there only has to be a 140 milliamp (0.14 Amp) drain to kill the battery. Any dinky little load will do that for you. Many electronics devices are continuous loads even when off. They do not really turn off, you only put them into a standby state awaiting orders to turn on again. We can thank smart electronics for that.

 

[mechanicjim]

if you plan on swapping to a dual voltage alternator, the load of the 12v should be taken from the battery not directly from the alternator 12v stud. the regulator was made to see a battery there it wont just output 12v from that stud if its not hooked up to a battery.

as to your add-on issues I suggest getting a power distribution block that way you can disconnect all add-ons at once to help with diagnosis/ repair and to help when you add more later on down the road.

 

[kc5mzd]

It is running on a brand new generator now, and it did this the first time prior to the replacement.

Below is a pic of my setup. The top battery is the rear, and the bottom is the front:
View attachment 668306

The battery in the top pic was made in 2013. The battery on the bottom has rust on it. The rust alone is enough to drain the battery and change the battery's resistance causing both batteries to charge at different rates. Walmart sells batteries for $50.00 Just find 2 batteries that are exactly the same size and weight (yes weight) with the highest cranking amps. Some smaller batteries are heavier and have more cranking amps. The heavier batteries have more lead and last longer. so for 100.00 you get 2 new batteries and should solve your charging issues. You will also get a warranty that will allow you to replace a battery that fails within several months of purchase for free.

 

[JLAINC]

Okay guys, so I've finally got back around to working on the HMMWV again. The first thing I have done is drop the fuel tank, which was actually more of a pain in the ars than I had expected it to be! Once I finally got the tank off the truck, and opened up the access plate on top, I was surprised to find the internal compartment to be in very good condition. very minimal debris in the bottom of the tank, and the intake sock looked to be in decent condition. Can anyone tell me the proper way to test the sock, and/or the best replacement for it? Since I have gone to the trouble of dropping the tank, I feel that I should probably go ahead and replace it. However, the sock appears to be permanently affixed to the tube, and you cannot remove the tube because of the sock! Whose idea was that???

 

[BLK HMMWV]

Get rid of the old style sender and upgrade to the new style while it's apart. You will get a better fuel level reading in the end.

 

[JLAINC]

Get rid of the old style sender and upgrade to the new style while it's apart. You will get a better fuel level reading in the end.

Where is the best place to find one?

 

[BLK HMMWV]

See if 86humv has one for sale here on SS.
Send him a PM or post a WTB new style fuel tank sender

 

[86humv]

Sock comes off with a twist...with pliers....then twist on a new one.
I'll see If I have senders.

 

[tbulloch]

If you have not solved or figured the reverse polarity yet, I have had this several times on my M35A3 when I leave lights on and run the batteries all the way down. Because they are in series, the better battery charges the weaker battery a little. So it essentially thinks it's hooked up parallel and charges it a little in reverse. This is not good for the batteries obviously but they are not shot usually. I've done this twice and my batteries are fine.

Just remove the batteries, charge the good one as normal before reinstall. But for the reverse one, hook up a light bulb or something to draw the battery completely down. I use an old trailer light. Leave it on a few hours after the light goes out to make sure it's discharged completely. Then use a manual battery charger and recharge it correctly. An automatic battery charger won't do it, you have to force push the correct polarity charge using a manual charger. It will be fine. Don't trickle charge it either, you have to force that first push with at least a 6-10a setting to get it to cross over.

You will still need to find out what's discharging your battery system as that's a separate issue, but reverse polarity is not completely unheard of in 24v systems using 2-12v batteries.

 

[JLAINC]

Sock comes off with a twist...with pliers....then twist on a new one.
I'll see If I have senders.

I tried to twist it off, but it appears to be crimped on with no threads. Can you tell anything from these pics:

 

[glcaines]

That sock appears to be in very good shape. I think I'd leave it alone and worry about your reverse charging issue if it was me.