Riddle me this: Jump starting a 24V vehicle

[Greg_B]

Someone un-named left thier headlights on today, and had to call BCAA for a jump start. They used the front plug-in most towtrucks have for the first connection (to the battery poles on the highside battery), then used a second jumper cable set to go from the second battery in the towtruck to the battery poles on the lowside. This connection could not be made as viscios sparking would result, and the cable heat up...and the truck would not start anyway.

He ended up removing the center battery cable, and charging each battery independantly for a while, then unhooked all the cables, hooked up the center cable and then the truck would start.

Am I missing something? I always thought as long as you did not introduce chassis ground on the 24V vehicle, you could go battery to battery from any 12V source, to both batteries in the 24V string and all would be ok?

Thanks

gb

 

[crushers]

yep, i have jumped the 24V system using 2 12V batteroes or vehicles, not disconecting eitehr of the 24V batteries and never had sparks. the jump truck probably had the batteries grounded to the frame... but then what do i know, i wasn't there.
are you going to install a headlight warning buzzer for Petra? or was it you that ooopsed?
cheers

 

[A2B in a TLC]

Gregory,

I had to jump last week when my charging system went funny. It was simple. But first I called our good buddy Allstone. Then the cabbie.

Anyway, I picked the stronger battery. But if you can't tell I'll bet it does not matter. Pretend that the other battery does not exist. Hook up as you would any 12V single battery: pos to pos, neg to neg. And jump. Started in a split second. No sparks.

The cabbie did ground to his frame. So it was not a complete post to post set up.

The price? $15.

Hope this helps. Was she fit?

B

 

[A2B in a TLC]

Hi again,

I am assuming the BCAA tow truck was 12V as was the cabbie's car in my example.....

B

 

[Greg_B]

yep, i have jumped the 24V system using 2 12V batteroes or vehicles, not disconecting eitehr of the 24V batteries and never had sparks. the jump truck probably had the batteries grounded to the frame... but then what do i know, i wasn't there. are you going to install a headlight warning buzzer for Petra? or was it you that ooopsed? cheers

I have too, and this is what is weird. I saw the hookup, and it looked fine, cept when the final connection was attempted. I must have been missing something obvious. Dunno...

Bruce, I usually have a voltermeter in my kit just for that reason. Cheap to buy, and you can check which one is stronger, then go to the weaker one to jump.

With another 24V close by it's easy...chassis ground on both, and high side positive pole on both.

gb

 

[Greg_B]

Are you going to install a headlight warning buzzer? cheers

Any ideas of ones off the shelf. I have not looked the net yet. Stone was thinking a relay pre headlight relay, that would take keyed power to activate and let power through to the headlight relay.

gb

 

[Greg_B]

Was she fit? B

I say nnnothhhhhing...

gb

 

[Whistler74]

Greg - thanks for the test drive today. I really hope that wasn't me that left your lights on - one of my many habits is turning things on, but not off...

 

[A2B in a TLC]

Greg said:
>>>
Cheap to buy, and you can check which one is stronger, then go to the weaker one to jump.
>>>

Sorry Greg, I said that I jumped off the stronger. It was indeed the weaker as Stone had suggested. Don't want to mislead... Pardon the pun.

B

 

[lowenbrau]

Second battery in the tow truck was connected in parellel to the first. He should have isolated it.

 

[Greg_B]

Greg - thanks for the test drive today. I really hope that wasn't me that left your lights on - one of my many habits is turning things on, but not off...

Nope, and no worries at all.

gb

 

[lowenbrau]

Second battery in the tow truck was connected in parellel to the first. He should have isolated it.

 

[Stone]

Second battery in the tow truck was connected in parellel to the first. He should have isolated it.

Is that what it was, Bruce? I don't know how they setup their batteries in tow trucks...but if that's the scenario then it would make sense.

Off topic: By the way, your modification to my trailer logic relay circuit works great. Both G&S and I are running them now. Thanks again, smart guy!

 

[fitchik]

;p ;p

I fess up....

Driving about this evening I have noticed that the Gauge reading the power of the battery is not where it used to be... it is weaker, but not in the red, just above the first white line (?). Has something happened to the batteries or battery that the Charge is not as strong as it was before this happened?

AND YES - am taking the suggestion of a friend, regarding a Buzzer to remind me I "left my lights on"

 

[fitchik]

Second battery in the tow truck was connected in parellel to the first. He should have isolated it.

K - Newbie question here: Bruce can you explain to me what you mean by "isolated" and in "parellel"?

Thanks

 

[crushers]

;p ;p

I fess up....

Driving about this evening I have noticed that the Gauge reading the power of the battery is not where it used to be... it is weaker, but not in the red, just above the first white line (?). Has something happened to the batteries or battery that the Charge is not as strong as it was before this happened?

AND YES - am taking the suggestion of a friend, regarding a Buzzer to remind me I "left my lights on"

maybe a dieing cell?

 

[Greg_B]

maybe a dieing cell?

Could be, though my experience with a 12V vehcile and a bad cell was an overcharging situation, as the alt was working OT. They are two mismatched older batteries I threw in as a temp solution. Guess I have to deal with it sooner rather then later.

gb

 

[fitchik]

Query: This morning I go to start the truck and the Gauge for Battery Voltage reads below the white line, then while driving the Gauge drops right down to the bottom line (red), lights go dim and I become a wee bit concerned...All of a sudden the gauge jumps up to above the white line and lights brighten up and away we go...

Could it be the the same issue as A2b in a TLC posted in a previous thread?

 

[crushers]

have you checked the brushes?

 

[ostacruiser]

So what would be the proper way to jump-start a 12v vehicle with a 24v vehicle? Just pos to pos and neg to neg on one battery? I'm asking cause winter is commin' and it never fails i always seem to be the one with jumper cables.