New batterys installed today.

jeeptj1 · Post by **jeeptj1** » Fri Mar 15, 2019 4:19 pm

Well got the new batterys in today and the old ones were for sure bad. However, the new ones still only register a little over 13 volts frame to positive or from negative post to positive post. Took the starter cables off and cleaned them up also. So then I fired the jeep up and noticed antifreeze pouring out. Have started it a couple of times this winter in the man cave and never had that problem. Couldn’t really tell where it was coming out of but maybe the overflow pipe. Could a bad radiator cap or stuck thermostat be the culprit. Have a lot going on next couple of weeks so might not get to this til it’s warmer out. Also is there a crossover number for the radiator cap. Thanks John jr

mdainsd · Post by **mdainsd** » Fri Mar 15, 2019 5:30 pm

Is your "little over 13 volts" with the engine running at speed?

You will have to narrow down where the coolant is pouring out.

There are supposedly NOS radiator caps on the big online auction right now. I picked up a few as the price is right. The one I put on seems to be working correctly, so far. Develops low pressure inside as designed. My old cap had long ago lost that ability.

jeeptj1 · Post by **jeeptj1** » Fri Mar 15, 2019 5:40 pm

Maybe I’m not understanding. Each battery is supposed to have like 27 volts correct? So if they each only have alittle over 13 volts, it’s not close to them being at the 27 plus each should be. John jr

RonD2 · Post by **RonD2** » Fri Mar 15, 2019 6:32 pm

No offense meant John, but I shot beverage out my nose on that one!

The military vehicle 24 volt system is two 12 volt batteries, connected in series. Each fully charged 12 volt battery normally puts out about 13.5 volts, multiply by 2 and you get 27 volts (typical good operating voltage).

I guess they call it a "24 volt system" because two 12 volt batteries connected in SERIES makes 24 volts. Not to confuse the issue, but two 12 volt batteries connected in PARALLEL is still 12 volts, but you get twice the amperage, but that's a different electrical class....

When you bought these new batteries today, didn't you buy two 12 volt batteries?

I highly suggest you double check you wired them up correctly before putting juice to anything. Big difference between series and parallel connected batteries. Hooking them up can be easily confused. The juice in a single 12V battery is enough to set you free (and weld unintended things together). Got a set of the tech manuals?

Good luck!

Post by **wesk** » Fri Mar 15, 2019 10:16 pm

Lot of terms getting tossed around with no references.

Let's start by separating two things. There are several combinations of words and numbers that describe very different things in our electrical system. Focusing on our 28 Volt Electrical systems:

1 - 28 Volt System means the "Operating System". It standardizes the reference to the operating system. When the system is in operation it's voltage reading will be 28 to 32 volts. This is the correct phrase to use when describing our jeeps military 28 Volt System

2 - 24 Volt System describes the system when it is not operating. That means without the generator output the system reads standing battery voltage which should be 24 to 27 1/2 volts. This phrase is the incorrect phrase to describe our jeep's military 28 Volt System!

3 - Some military vehicles use a single 24 volt battery and some use a pair of 12 volt batteries connected in series. Our jeeps use a pair of 12 volt batteries connected in series. Series means the #1 battery has 24 volts total at it's + terminal and the #2 battery has 12 volts at it's + terminal. The #1 battery's + terminal fastens to the starter and it's - terminal connects to the #2 battery's + terminal and the #2 battery's - terminal connects to the frame ground.

4 - With a 24 volt type battery installed and connected and fully charged it will read 25 to 27.5 volts at it's + terminal.

5 - With a pair of 12 volt batteries connected properly in series and fully charged the reading at the #1 Battery's + terminal will be 25 to 27.5 volts.

6 - If you disconnect both 12 volt batteries and they are both fully charged they should read 12.8 to 13.5 Volts.

7 - When any standard military 28 Volt System is operating properly no matter weather the battery is a single 24 Volt or Dual 12 Volt they will read at the + terminal connected to the starter 28 to 32 volts.

RonD2 · Post by **RonD2** » Fri Mar 15, 2019 11:23 pm

As usual, Wes clears up my apparent lack of references. Yes, references are important. In this case, somewhat superfluous to John's question about why a 12v battery isn't measuring 27 volts? Me thinks John has a more fundamental misunderstanding about the nature of electricity, and hasn't read the TM either. (No offense intended John!) I'm just trying to offer some friendly advice. References come after. Isn't that what this forum is about?

(Almost) Bottom line: there's no way one new 12 volt battery should read 27 volts. Ever. For the M38, it takes two 12-volt batteries properly connected in series to read anywhere near 24 (or 28 ) volts. Am I wrong?

John said he started his engine with the new batteries installed. I wonder. Would a 28 volt starter motor crank and start a L134 if the batteries were incorrectly connected in parallel (producing 12 volts instead of 28 volts)? Just curious.......

Can I muddy the water or what?

OKCM38CDN · Post by **OKCM38CDN** » Sat Mar 16, 2019 6:25 am

The batteries are connected in SERIES... thus their voltage adds; two 12 volt batteries when new usually measure some where in the range of 12.5 to 13.4 let say. Now we put them in series and the voltage goes to 25.9 in this instance. that is enough to drive the 24V starter and 24V coil. When the engine fires and the 24V Generator takes over the batteries generally will charge at 28.x volts plus or minus a little bit.

If you parallel the batteries the amount of current the batteries give increases. This is a way to give more starting current to a starter if it will not run, In this instance the current adds and the voltage stay the same.

Thus if you placed two 12 volt batteries in PARALLEL then their 500 amp starting current would double to 1000 amps, but the voltage will stay at 13.4 for this example.

I give this explanation so as to be sure everyone understands how the batteries work in a given configuration...

I worked with batteries in telecom industry for 45 years and understanding the way they work insures the proper length of time they will last and that the equipment using them does the same...

Thanks for the time...

Post by **wesk** » Sat Mar 16, 2019 10:56 am

Now since we have managed to muddy the water again!

Two 12V batteries parallel will actually turn over a 28V starter. Just not very quick and of course depends on the condition of the starter.

To take all this another step backwards to basics:

Volts = Pressure
Amps = Ability to do work

RonD you were not the primary target of my comments but since you moved on to attempt to grade the quality my comments:

somewhat superfluous to John's question about why a 12v battery isn't measuring 27 volts?

My comments were not meant to be an answer to his original question! They were meant to clear up the muddy playing field ya'll laid out for him!

RonD2 · Post by **RonD2** » Sat Mar 16, 2019 11:10 am

Thanks Wes. No offense was intended to you either. For a couple of old guys, we sure have our fair share of thin skin?

I don't think our comments either laid or cleared up a muddy field. It's just that difficult if not impossible to teach or provide a coherent basic direct current electricity course to a novice in this or any other forum kind of environment. But we all try in our own way, don't we?

This might help? Then again, it might not.
http://hyperphysics.phy-astr.gsu.edu/hb ... atcir.html

Maybe all we did was successfully hijack the thread?

Post by **wesk** » Sat Mar 16, 2019 1:37 pm

Well whenever you guys all agree that the thread has been hi-jacked and we've strayed too far from the original topic just post me a 100 % agreement and I can dump all the BS.

But as long as each poster adds unclear or incorrect data I will always try to correct or make it more clear for everyone's benefit.

RonD2 · Post by **RonD2** » Sat Mar 16, 2019 2:04 pm

That's why we love you!

4x4M38 · Post by **4x4M38** » Sat Mar 16, 2019 2:54 pm

Heh.

I wait patiently for John Jr’s response...

RonD2 · Post by **RonD2** » Sat Mar 16, 2019 4:16 pm

Me too! I hope I didn't tick him off, or worse.

I also hope he didn't buy two new batteries for nothing........

John?

dpcd67 · Post by **dpcd67** » Sat Mar 16, 2019 5:11 pm

All good information for the OP.
However,, I sense that he has not read his Operator's and Org maintenance
TM. Unfortunately, that is a common trait among MV owners.
I spent two careers trying to get soldiers, and then civilians, to read their TMs. Like pulling teeth.
I encourage every MV owner to own and read, all the TMs including the SNL, if he is to learn about his system. Yes, I see those who just want to drive them and don't care about learning the old fashioned way; reading. Sad.
My answer to him would have been, "What did your TM9-8012 say? Hint, it's on page 197-198 in the Jan 56 edition.
I read mine every day for various vehicles.