Charging Batteries

[Kambaku]

I am interested in how you would hook up a suitable 24V charger to charge the entire battery bank (all 4 simultaneously, not disconnected). To that end, If you take a voltage reading from the left rear battery positive battery post to the right front battery, negative post you get 24VDC. This is diagonally across the entire battery bank. Is this a suitable connection point for the charger to hook up?

Thanks

 

[o1951]

I am interested in how you would hook up a suitable 24V charger to charge the entire battery bank (all 4 simultaneously, not disconnected). To that end, If you take a voltage reading from the left rear battery positive battery post to the right front battery, negative post you get 24VDC. This is diagonally across the entire battery bank. Is this a suitable connection point for the charger to hook up? Thanks

Yes.
I do not like charging at 24 volts because the batteries that supply the 12 volt system often need more charging time than the other 2. The batteries would need equalizing charges to prevent early failure.

 

[Kambaku]

I appreciate your technical insight in this regard. I was looking and hoping for an easy solution. When I charged my batteries in the past I disconnected all the terminals and charged each individually. It took time and effort to do this, but my takeaway from what you said is that this is the right way to do it. Disconnecting everything and putting things back together is actually the biggest hassle. Letting the charger sit is just time. To speed up my charge cycle would you or others recommend a high amp output charger. "High" is relative I know, but there has to be an optimum method. I think my current charger, albeit a good one is adequate if you're okay letting things charge for a couple days but...

 

[o1951]

I appreciate your technical insight in this regard. I was looking and hoping for an easy solution. When I charged my batteries in the past I disconnected all the terminals and charged each individually. It took time and effort to do this, but my takeaway from what you said is that this is the right way to do it. Disconnecting everything and putting things back together is actually the biggest hassle. Letting the charger sit is just time. To speed up my charge cycle would you or others recommend a high amp output charger. "High" is relative I know, but there has to be an optimum method. I think my current charger, albeit a good one is adequate if you're okay letting things charge for a couple days but...

Slow charging is always best - only thing better is a pulse charger. I see no reason to disconnect everything, unless you have an undiagnosed parasitic load.
As built, it has 2 sets of 12 volt batteries in parallel. If electrical system is working properly, no reason I know of why you cannot charge each of the 12 volt sets with all cables connected. You would be charging one parallel 12 volt set (2 batteries in parallel) at a time. You should have a hydrometer or good meter so you know when each bank is fully charged, and you are not overcharging.

I have tried to explain as clearly as possible, intentionally repeating.
Don't go out there after a few too many beers and mess things up by accidentally connecting the charger across 24 volts.

Of course, the usual disclaimer. Do not listen to anything I say, I do not know what I am talking about and am off my meds.

 

[Kambaku]

Thank you, your response is well written and clear to me. I understand what you are saying about parasitic load as well. What took me down this path in the first place may or may not be related to that point.

I parked my my truck for about an 8 week period this summer. When I came back the truck would not start. A thorough battery charge remedied this. At that time I pulled all the cables and charged them individually. Since that incident I have been turning off the master battery switch each time it is parked. Following this procedure, I have not had any starting issues. This would indicate that something(s) was drawing current. Not unusual, e.g., ECM.

Disclaimer appreciated but but not necessary, I thank you for your help.

 

[NDT]

I just picked up an M916 from Texarkana TX. The voltage regulator is bad so it would not charge the batteries while driving. We used 2 sets of jumper cables every night to recharge the batteries from the dual battery chase truck. The chase truck is 12 volt only, so the 24/12 volt battery pack on the M916 had to be slightly rewired by moving one wire. This works in a pinch.
View attachment 599248

For future reference, the M915/M916 series trucks (pictured) has the RIGHT pair of batteries connected in series with the LEFT pair of batteries. This is different from the FMTV trucks where the FRONT battery pair is connected in series with the BACK battery pair.

 

[o1951]

For future reference, the M915/M916 series trucks (pictured) has the RIGHT pair of batteries connected in series with the LEFT pair of batteries. This is different from the FMTV trucks where the FRONT battery pair is connected in series with the BACK battery pair.

On any vehicle that is new to you, always trace out cables and confirm how the batteries are wired. After all these years and being worked on by various people, someone could have changed wiring. They will work just as well wired front/back or right/left. Slave port will work wired either way. To keep the magic smoke inside, must know how it is wired when hooking up battery charger.

 

[scottmandu]

http://www.instructables.com/id/Simplest-Chargerdesulfator-Ever/

 

[emr]

Simply put. Any and all batteries can be charged while hooked up with a 12 volt charger on each. Or you can use one charger and move it from battery to battery until all are charged, >>> Eventually in parallel both batteries will be charged, BUT That is NOT completely true. the second battery will when almost full put enough resistance for the charger to stop so it does not over charge the first. So the second will sulphate faster and die sooner, Unless they are fully charged annually and rotated. In Series a 24 volt charger is just like the vehicle charger and the same thing happens, The batts in the end of the line never get fully charged and will die sooner, Oh yes they will.

These big batts need a charger that will put out 13.6 volts and should be smart enough to change voltage to what the battery will take to become fully charged, if U only use a 2 amp they will not only take forever they will stop before fully charged because they will have to fight the big batts resistance. And never go deep into the batt A batt can say its full with out the bottom being fully charged, This happens with sulphated batteries also ,

A 15 amp per say charger will put a charge in that will fill the big batt, But remember again there is a catch, A 15 amp charger will stop short of an ACTUAL full charge so not to over charge the batt. After a 15 amp charger did its job THEN hook up the 2 amp and you will see it will still charge ) and that will actually fully charge your batt. Its only topping it off not trying to push a charge deep into batt.

There are now chargers now that will send different pulse through out the charge cycle to charge ALL batts in a parallel situation up to 5 that I know of, But remember our and all vehicle charging systems are NOT smart and will just do what is excepted as full in the indusrty.