Jump starting using 12v systems

[sallystrothers]

What's the recommended procedure for jump starting the HMMVW 24v? using 12V? I have two automotive 12v jump start battery packs and was thinking of putting each 12V pack in parallel of each 12V batterybattery. Another option is a single pack on one of the two batteries and hope it has enough amps to crank the engine, and the last option is the jump start packs connected in series, making them 24V and then in parallel to the - side and the +24V side of both batteries. What is the actual operating voltage of a HMMVW while the alternator is running?

 

[Coug]

running voltage is just over 28VDC (28-28.8VDC)
Each battery will be at about 14-14.4VDV when vehicle is running if the charging system is functioning properly.
At rest they'll be somewhere around 12.6V or higher. Below that is a drained or dead battery.


Depending on the style of alternator/generator in your HMMWV, slight differences in what to do.
If it's the 60 amp generator, then it's going to be more likely that the second or rear most battery is the one that is dead or failing, as they don't always balance properly when charging. Especially true if there is ANY 12V outlet/device wired in to just that battery. If you have a single 12V jump pack, try jumping just the rear battery. If they are both dead or low, follow the below advice.

If you have a dual voltage charging system, then my recommendation would be a separate 12V jump pack wired to each battery. In theory each battery should get power to it to keep it charged up, so unlike the 60 amp system there won't be one battery undercharging all the time. (side note, on the 60 amp system it's a good idea to switch the batteries every month or two, so they get charged more evenly and will have a longer lifespan)


If it's dead because one battery is weak or failed, then you should only have to jump that one battery. You'll want to get both batteries replaced as a set to get the best life out of both of them, as adding a new battery in series with an old battery may place additional stress on the new battery and shorten it's lifespan.
If it is dead because someone decided to leave the key switch to "on" and the headlights on, or someone wired something directly to the batteries and they are both drained down, then you'll definitely need to jump both, or charge them individually.


I would recommend AGAINST trying to use any lithium jump packs in series, as they tend to have electronics in them that might not like higher voltage (in theory each jump pack should ONLY see 12V, but theory and real life don't always agree). The bigger, heavier lead acid battery packs you can run in either series to get 24V or in parallel with the batteries and not worry too much.

 

[snowtrac nome]

its real simple hook up positive and negative clamps to the appropriate battery termanals

 

[DREDnot]

If it's the 60 amp generator, then it's going to be more likely that the second or rear most battery is the one that is dead or failing, as they don't always balance properly when charging (side note, on the 60 amp system it's a good idea to switch the batteries every month or two, so they get charged more evenly and will have a longer lifespan)

Ive been getting the occasional blinky wait light recently and after reading this, I took a voltmeter to the batteries after disconnecting them and sure enough...front battery was at 12.8v rear was at 12.0v

I have now cleaned and swapped them and the low one is on a charger to see what happens

 

[sallystrothers]

Thanks, will give it a shot, vehicle is being delivered on Sunday and "runs after jump starting" according to govplanet, its an '04 m1123

 

[TOBASH]

Would you start your old Chevy with a 6 Volt battery?

Get a 24 Volt charger or buy new batteries as my suggestion.

 

[Coug]

Thanks, will give it a shot, vehicle is being delivered on Sunday and "runs after jump starting" according to govplanet, its an '04 m1123

Pretty much every vehicle I've heard that was described as "runs after jump starting" doesn't have batteries in it.

If it DOES have the batteries, there's an even chance they'll be toast, but some chargers like the NO.CO have a repair function that may or may not save them with enough persistence. More than a few threads on here discussing what batteries work or don't and about how much you might spend on them (I've seen pics with batteries that cost $100 for the pair up to one picture where someone snagged use batteries from a helicopter that would cost $800 for the pair. My pair cost $600 with full 5 year warranty, but aren't 6TL sized)

 

[Coug]

Would you start your old Chevy with a 6 Volt battery?

Get a 24 Volt charger or buy new batteries as my suggestion.

Not quite sure where the 6 volt question came from. If it's related to the charger he is using it looks like a 12V 6 amp charger, which is just fine for charging one at a time.

 

[TOBASH]

Not quite sure where the 6 volt question came from. If it's related to the charger he is using it looks like a 12V 6 amp charger, which is just fine for charging one at a time.

My point is use the correct charger for the correct job. 24 Volts is 24 Volts is 24 Volts. It is not 12 Volts.

Best to you Coug and OP,

T

 

[Coug]

My point is use the correct charger for the correct job. 24 Volts is 24 Volts is 24 Volts. It is not 12 Volts.

Best to you Coug and OP,

T

I would argue that for 2 12V batteries in series with nothing to balance them, using a 12V charger on the one battery that is undercharged WOULD be the correct tool for the job, because a 24V charger will still overcharge the one battery in order for the lower charged battery to be brought up to charge.

 

[Curtisje]

I have both. A 24v charger and a few 12v chargers. Charging my batteries independently each with a 12v charger ALWAYS yields better results.

 

[DREDnot]

Thanks, will give it a shot, vehicle is being delivered on Sunday and "runs after jump starting" according to govplanet, its an '04 m1123

That's how mine was.
Had batteries but from 2010

Everything at auction just about comes with dead/no batteries. They just slave start them...which is the preferred method of jump starting. Fast, and PVT Goof-proof .

I had pre purchased two new 6TL batteries from O'reillys for 200 each, new clamps, and new center cable to be able to fire it up to get it of the trailer when I got it home.

 

[sallystrothers]

Pretty much every vehicle I've heard that was described as "runs after jump starting" doesn't have batteries in it.

If it DOES have the batteries, there's an even chance they'll be toast, but some chargers like the NO.CO have a repair function that may or may not save them with enough persistence. More than a few threads on here discussing what batteries work or don't and about how much you might spend on them (I've seen pics with batteries that cost $100 for the pair up to one picture where someone snagged use batteries from a helicopter that would cost $800 for the pair. My pair cost $600 with full 5 year warranty, but aren't 6TL sized)

No batteries. I did scrounge up two regular car batteries. It cranked with smoke coming out of the exhaust but would not fire up. Will be researching how to get it running. I need to drive it about 30 yards to its restoration location.

 

[Coug]

No batteries. I did scrounge up two regular car batteries. It cranked with smoke coming out of the exhaust but would not fire up. Will be researching how to get it running. I need to drive it about 30 yards to its restoration location.

I ran mine for the first few months on a pair of old car batteries. I've heard stories though that if the batteries aren't the same size/capacity, bad things can happen, so as soon as I got mine licensed (about 4 months after picking it up) I splurged on a GOOD pair of batteries. Not Hawker or Odyssey 6tl AGMs, but the next best thing (and half the price with full 5 year warranty).

X2Power Premium AGM BCI Group 24 Car and Truck Battery - SLI24AGMDP at Batteries Plus Bulbs

X2Power group 24 AGM replacement battery designed for low maintenance and dependable engine starting power. Designed for Volvo, Pontiac, Subaru, Dodge and more

www.batteriesplus.com

If you have smoke then you should be getting fuel (at least a little) so I'd be checking on the glow plugs/starting system electrical.

Here is a decent run down of what all to check

Help! My HMMWV Won’t Start! Humvee Wait Light Glow Plug and Start System Information and Maintenance | Gear Report

There are LOTS of symptoms and reasons why a HMMWV might not start normally. In this article we will cover some of the most common...

gear-report.com

 

[sallystrothers]

I ran mine for the first few months on a pair of old car batteries. I've heard stories though that if the batteries aren't the same size/capacity, bad things can happen, so as soon as I got mine licensed (about 4 months after picking it up) I splurged on a GOOD pair of batteries. Not Hawker or Odyssey 6tl AGMs, but the next best thing (and half the price with full 5 year warranty).

X2Power Premium AGM BCI Group 24 Car and Truck Battery - SLI24AGMDP at Batteries Plus Bulbs

X2Power group 24 AGM replacement battery designed for low maintenance and dependable engine starting power. Designed for Volvo, Pontiac, Subaru, Dodge and more

www.batteriesplus.com

If you have smoke then you should be getting fuel (at least a little) so I'd be checking on the glow plugs/starting system electrical.

Here is a decent run down of what all to check

Help! My HMMWV Won’t Start! Humvee Wait Light Glow Plug and Start System Information and Maintenance | Gear Report

There are LOTS of symptoms and reasons why a HMMWV might not start normally. In this article we will cover some of the most common...

gear-report.com

Thanks, that link is very helpful. I was able to tow it off the street for now and I can take more time to troubleshoot. I do have a question, I can't figure out where this plug goes. I have a troop carrier and was suspecting it powered some kind of accessory in the rear.

 

[Coug]

Thanks, that link is very helpful. I was able to tow it off the street for now and I can take more time to troubleshoot. I do have a question, I can't figure out where this plug goes. I have a troop carrier and was suspecting it powered some kind of accessory in the rear.

Looks like the radio power supply cable. Comes up through the floor near the doghouse, right?

 

[Coug]

So for some reason, even with a battery disconnect, my batteries were dead this morning (after sitting almost 2 weeks, voltage under 4.5V each battery)

I figured I'd post a picture of how I set up the 12V jump boxes, as some people are more visual in their learning (and words can be confusing)


engine off, just power from the jump packs. ! box per battery, directly to the battery posts/clamps.


Engine running and batteries charging.

 

[kendelrio]

So for some reason, even with a battery disconnect, my batteries were dead this morning (after sitting almost 2 weeks, voltage under 4.5V each battery)

I had the same issue with my 5 ton. I found out that when my batteries were turned off at the dash I still had power going to my dash gauges. Lacking the time (at the time) to completely troubleshoot the issue (I'm flying in from offshore today so will make time over the next month off to find and fix) I bought a heavy duty battery disconnect switch from NAPA and put it inline with the positive side of my batteries. With that, I completely disconnect the batteries from the circuit and have had no trouble with dead batteries since. (It's also a good anti-theft device because I've hidden it, so even if someone knows how to start my truck, good luck finding the disconnect).

 

[M1165A1]

Anyone using a 24 volt trickle charger, like this one?

Amazon.com

 

[dhaumann69166]

If you need to jump start it just hook one vehicle (or charger) to one battery like you normally would and then hook your second vehicle or charger to the other battery like you normally would. That way you are getting 12v (14.4 ideally) to each battery. If you hook positive lead from charger or vehicle to positive connection on one battery and negative on the other with anything other than a 24v rated system you will be buying some new batteries and electronic components for your jumper vehicle or charger.