89 M998 Low Charge Indication

[15N AVI 998]

Hey all,

Trying to get this typed up before my laptop dies. Over the last few weeks, my 998 has been showing a low charge indication after warm up and during driving. I'm still running the 60 amp generator on it, which was recently replaced, and have cleaned all connections that I could access relatively easily (I think I only missed one). Doing voltage checks, I have 28.1-28.3 (maybe 28.5 momentarily/intermittently) on the gen and at the batteries, but only charging at 5 amps or less immediately after starting (checked with a Fluke clampmeter). What has me concerned is that the voltage at the igniton/sense lead (?) is only 14-14.5 (varying slightly), maybe causing the low amperage output.

I've recently installed a cutoff switch at the batteries (in a way that still enables jump starting (however unintentional). Jumping the truck from a generator trailer and then disconnecting (yes, I forgot I had the disconnect switch off) the charge indicator was right at the "tick mark" in the green field with a slight high frequency shake of the needle. Turning the batteries on brought the needle down to just under a quarter charge indication, with a stable needle.

I'm wondering if anyone else has had this issue and what was done to correct it. From what I'm seeing in schematics for other model HMMWVs, the EESS or protective control box (?) provides the necessary excitation/control voltage for the gen to function as needed. Really hoping I don't have to change out a control box.

Standing by for suggestions, or legible electrical drawings.....

 

[papakb]

That small lead (56B) is the alternator exciter wire and should be 24v. Jumper the alternator output stud to it and see what the output goes to. If you look at the schematic you'll see that's the way it's normally connected.

 

[Mogman]

I would suspect the ammeter, 28.3-5V is not bad.
Do you have GOOD matching batteries?
With that kind of charge voltage you should not be having to jump it off.
Are you sure you are not measuring the AC terminal (2A)? instead of the sense term.?
There should be 24V on the sense terminal not 14V.

 

[15N AVI 998]

I did have a battery go tengo unfiorm on me (which prompted the jump), top charged the remaining good battery and installed a new battery after top charging it as well (I forgot to mention that tidbit). I'll be rotating battery positions monthly from now on. I'll try a continuity check in a lil while once things dry out some, had some storms roll through later last night. If nothing else, I'll fab a jumper lead to go in place of 56B and see what comes of it.

 

[Mogman]

You will continue to loose batteries and have problems as long as you replace one at a time.
You should always replace both the batteries and should try to get matching batteries and with the same build date if you can.
Certainly not the cheapest route but then again you gave up the right to cheap when you bought a Humvee

 

[MarkM]

Dual batteries require batteries of the same age and potential and preferably share the same lot numbers. Differing batteries in a Dual (or more) system will cause one of the batteries to be over charged and the other to be under charged. Causes nothing but problems. Think of it as one giant battery and all cells need to be equal. Just my two cents.

Mark

 

[15N AVI 998]

I understand the concerns about the differing battery dates and such. I plan to start working the batteries the same way as an aviation maintenance facility (at which I work) in that regular charge, discharge, and capacity testing will be done. Both batteries were top charged before being installed, and the removed battery is undergoing a condition charge. I haven't been able to test the harness on the engine for continuity yet as work and family plans have somewhat intervened. Hopefully I'll be able to get around to checking wiring later this morning/early afternoon.

Papakb, would you happen to have the full schematic for a 998?

Standing by.....

 

[MarkM]

I take it you are an A&P ?



Mark

 

[Mogman]

Again, you will continue to have electrical issues as long as you run miss matched batteries, this has been proven time and time again.
Why would you saddle yourself with a maintenance nightmare just to save a few bucks?

 

[15N AVI 998]

I have my airframe cert, and as soon as time and travels permit, I'll try to test for my powerplant cert.

As far as a maintenance nightmare, I'm not looking at it as such, I know driving this thing is expensive, and we knew that going in, especially since the vehicle is a daily driver. Owning and operating it as such has been an evolving experience since its purchase.

 

[MarkM]

Two relatively inexpensive flooded 6TL batteries of the same potential is far more desirable then adding one new battery to an old one and chasing gremlins.

Believe me I get proper voltage and capacity testing but few here have the knowledge or equipment to take on that technical task and why would they. Best recommendation is always when possible to install paired same potential and preferably same lot numbers to avoid issues. That's all I'm saying.

Mark

 

[15N AVI 998]

I only recently found a connection for not as expensive batteries (I was going through Napa, paying almost 500 a pair, if they could get them). Just checked both of mine and they're at 12.85 and 12.88 so they're definitely taking and holding charge, they discharge fine with the engine cranking over no problem. I just can't help but to think there's something in the charging system that's being "lazy". The engine harness rings out good, with all connections at a half ohm or less (with most of that resistance being from my test leads/adapters.

In regards to the "AC" terminal, what's its purpose and intended output? I'm having a time trying to find info on it in the TMs.

Standing by.....

 

[Mogman]

It tells the Protection control box the engine is running and on some units it drives the tach.

 

[FlameRed]

I only recently found a connection for not as expensive batteries (I was going through Napa, paying almost 500 a pair, if they could get them)

Not to hijack your thread, but if they are the equivalent of the Exide military ones, that is a deal as the ones I have found are more than $500 each. Mind posting some NAPA part numbers or other details?

 

[Mogman]

Not to hijack your thread, but if they are the equivalent of the Exide military ones, that is a deal as the ones I have found are more than $500 each. Mind posting some NAPA part numbers or other details?

I don't think anyone would consider that question hijacking,,

 

[Mogman]

I use Odyssey batteries, and I am just as cheap as the next guy, some things are just worth the extra money.

 

[Coug]

Not to hijack your thread, but if they are the equivalent of the Exide military ones, that is a deal as the ones I have found are more than $500 each. Mind posting some NAPA part numbers or other details?

current military ones are AGM technology, and civilian equivalent are $500+
The ones most people find at the parts stores are flooded lead acid. Oldschool technology.

 

[MarkM]

I run two red top Optimus and love them. I would prefer two Hawkers but I just can't justify that price.

Mark

 

[15N AVI 998]

6TL is the battery number, pretty well universal across the different parts store chains. The guy I'm talking with now is a neighbor that just recently started with Autozone. Supposedly can get the batteries for about 2/3 the price I was spending at Napa.

 

[Bulldogger]

Have you checked the connection on the opposite side of the + post that leaves the battery compartment? The 24V+ lead leaves the battery compartment in the front left corner by attaching to a post, not running the cable through the wall (at least in my HMMWV). That post has a 24V+ lead to the engine/starter/etc. on the outside terminal. I was having trouble like yours and kept checking connections for tightness, when I realized the 24V+ going out of the battery compartment just HAD to have a connection on the back of the post. It was indeed loose, and I've been worry free (more or less, it's a HMMWV) since I tightened it. One word of caution, you'll be tightening/checking a 24V+ nut about 2" from the starter body. Wrap that wrench to prevent grounding it out!
Hope this helps.
Bulldogger