Starting current peak draw, slave port

[NormB]

Okay, looked through the manuals, this one's been on my mind for awhile as I'd like to place some circuit breakers in strategic locations.

One place in particular is the slave port. Have a jumper cable (thanks JuanPrado for parts), generator - with TWO dead, toast, Optima yellow tops (it's okay, amazon refunded $$$$ from 18 months ago) replaced with flooded cell lead-acid batteries.

Wondering if I ever need to jump the truck (6.2L NA), how much current will be going through those cables (20 feet) and the slave port?

Stuff happens. I've seen some pretty good fireworks in the past in cars that had some mysterious short that only became obvious once the cables were connected. A circuit breaker inline would've prevented the meltdown I'd think.

Overkill? Never been a problem before? There really aren't a lot of fusible links in the circuitry on these trucks. Surprisingly, as they're all over modern cars out of Dee-troyt.

So if someone could throw me a bone here, if you know for sure, or better yet, can direct me to one of the manuals where this is discussed/outlined/specified, I'd appreciate it.

 

[98G]

Consider not just the current when slaving the hmmwv and its relatively modest requirements. Consider also if someone were to slave a bigger vehicle from the hmmwv.

1000amps seems not unrealistic and perhaps not sufficient...

 

[papakb]

Your probably looking at around 200 amps max thru the connector. The NATO connectors themselves are rated at 1000 amps for 6 minutes and 500 amps continuous.

I once slaved an M1 Abrams from my HMMWV at an airshow.

Remember to have the engine OFF when slaving other vehicles. Starters draw beuacoup current and if the alternator tries to supply all of it your going to end up buying one.

 

[Milcommoguy]

Here's where that funny fined - thingie located in the battery box, tunnel side, front battery is for. It is a "SHUNT" and is there to do exactly what you want. With a voltmeter you can convert the small voltage drop across this shunt and determine / calculate the current / Amps. The ratio is 100 milivolts = 1000 Amps and is proportional so do the math. 50 mv = 500 Amps, 25mv = 250 Amps and so on. Or multiply miliivolts by 10 to get Amps. Slave receptacle is not going thru shunt. It's harder to remove the seat.

Were getting down to pretty to small voltages so using a digital voltmeter on a very low scale for best accuracy. If this is making sense... The shunt and the way the shunt is wired into the negative lead will be a big BIG help in diagnosing high current draw like GLOW PLUGS & starters .
(not so much lights or sneak currents do to resolution as in less than 10 amps )

Fancy Fluke DVM (Digital Volt Meter) with a peak and hold feature you will be able to get a "snap shot" on the peak Amps like starter and glow plugs currents.

From the.. READY for it >> TM > http://hummer-hmmwv.tpub.com/TM-9-2320-280-20-1/css/TM-9-2320-280-20-1_407.htm

As for FUSES... My belief is the Hmmwv wiring is about as simple as it gets. Would have been nice to have colored wires but black works. Couple of circuits breakers (behind dash) to protect the little stuff (lights, fan, wipers, wires) everything else essential, hard wired for battle. Can't be fooling around looking for the starter fuse with bullets are flying around. If you do fuse IT... carry spares. High amperage fuses can be hard to find when they blow.

So there you go. Be careful, think it thru and don't Fluke it up.

CAM

 

[98G]

Your probably looking at around 200 amps max thru the connector. The NATO connectors themselves are rated at 1000 amps for 6 minutes and 500 amps continuous.

I once slaved an M1 Abrams from my HMMWV at an airshow.

Remember to have the engine OFF when slaving other vehicles. Starters draw beuacoup current and if the alternator tries to supply all of it your going to end up buying one.

I concede you may know something I don't.

Here's some relevant experience i have -

Welding with 2/0 cable all day at 225 amps and the cables don't get warm.

Slaving a 5ton truck using slave cables made from 2/0 cable and they're too hot to touch after just a bit of cranking.

Batteries are 650 amps or so, and wired series and parallel on the 5ton trucks. This leads me to believe that someone intends to send over 1000 amps at 24v somewhere... (obviously just momentarily).

I'd hate to lose compatibility with other military equipment.

 

[Milcommoguy]

Ooops...The cutie bear icon messed up. This TM link give the starter dope. > http://hummer-hmmwv.tpub.com/TM-9-2320-280-20-1/css/TM-9-2320-280-20-1_353.htm

Slave connector not so sure, but if "papakb" jumped a tank... then more juice or honey for most bears.

Says Pooh,

CAM

 

[Milcommoguy]

Here's another chart for comparison. https://www.iewc.com/-/media/iewcglobal/files/resource-downloads/welding-cable-ampacities.pdf

Voltage drop and available current verses distance to where you are looking to supply are the allowable factors. The welding process for "welding" allows for a set voltage drop of 4 volts over the distance charted. Those 2/O cables on a big deuce and ??? what distant are U going ??? sure could smoke after a few tries. Last time I tried to haul cables, it was like fighting with a charged fire hose.

AND with all the fried not so smart boxes, I might rethink playing triple A.

Charging ON,

CAM

 

[98G]

Here's another chart for comparison. https://www.iewc.com/-/media/iewcglobal/files/resource-downloads/welding-cable-ampacities.pdf

Voltage drop and available current verses distance to where you are looking to supply are the allowable factors. The welding process for "welding" allows for a set voltage drop of 4 volts over the distance charted. Those 2/O cables on a big deuce and ??? what distant are U going ??? sure could smoke after a few tries. Last time I tried to haul cables, it was like fighting with a charged fire hose.

AND with all the fried not so smart boxes, I might rethink playing triple A.

Charging ON,

CAM

The welding leads used are 15'. Slave cables are typically 12' and 20'.

It's a relevant comparison due to the same cable diameter, and the fact that in welding you know exactly what the amperage is. From this we know that 200ish amps doesn't heat 2/0 cable, but slaving a vehicle quickly does. Therefor we can conclude that slaving involves more than 200 amps.

The nice thing about military equipment is that it is all mutually compatible. It's very convenient to be able to slave the HMMWV from the generator and the 5ton from the HMMWV etc. I'd hate to lose that capability by placing a limiter into the slave port. While it might not matter to the OP, a subsequent owner may have other equipment and would anticipate the slave port to function at original spec.

This reminds me of the guy who converted his vehicle to 12v and kept the slave port functional at the new 12v spec. He made a set of slave cables with a NATO plug on one end and alligator clips on the other. This was intended to be a slick way to slave to and from civvy vehicles (and it surely was). The problem arises when someone else sees a slave port that's compatible with 24v and connects it to a 24v application.....

Norm's result wouldn't yield that type of fireworks- just a blown fuse. Still, I think this is a solution looking for a problem. I'd leave this portion of the electrical system alone. I'd leave the slave port hardwired to the batteries and put any fusible links between the batteries and the rest of the vehicle.