Thread: Jump start points outside battery box

Originally Posted by Gibs

what ever, you go right ahead and burn ya truck to the ground, I'll motor safely right past you. My 40 odd years as an Elec Eng means I'm as happy as with my statement, not yours. Good bye.

So Gibs, what you are saying is, you actually have no proof what so ever to back your claims of armageddon unless someone use cabling as thick as your arm.


Well I am NOT an engineer of any form, so I do what most SMART people do and use the info that REAL electrical engineers make available for people like me.


Folks, next time you want know which cables can be used for what job, do a google for Cable Amp Rating Duty Cycle Charts.


There are dozens of them and they are there for the use of anybody looking for REAL info about cabling.

where to start...

Yes a battery has the potential 700CCA .. this just means it can deliver 700A for 30 seconds at -18C .. AT THE TERMINALS.. in the real world starter motors have resistance, cables have resistance, clamps have resistance.

Shall I be generous and say there is 50 milliohms in the whole circuit?.

Simply ... I=V/R

I will assume we have 14V as it is within engineering tolerances (and what I would expect my running motor to be sitting at)..

I end up with a current value of 280 Amps.

A quick reminder that this is a inductive load, not a capacitive one ...you know - series wound motor, lots of wires .. and what that means.

Starter motors will have an initial high draw current (stall).. limited by the resistance of the circuit .. as we just calculated that will be just under 300A ... then current will then REDUCE to the what ever is required to keep the engine rotating.

35mm cable will handle that for 30 seconds without melting anything (remember what CCA means). In fact 35mm cable will need over 1000A continuous before it will start to melt.

As for the connectors... Andersons 175A have a UL rating of 280A* .. what a coincidentally lovely number

Very happy to discuss any of the electrical calculations I have made

Regards

Wally

References (using wikipedia for convenience):
Ohm's law - Wikipedia
Engineering Tables/American Wire Gauge - Wikibooks, open books for an open world
http://andersonconnect.com.au/store/...s/DS-SB175.pdf

*with 50mm cable

Those little lithium power packs that are now capable of starting even the 4.5l V8 in my 79 series have only got piddly little cables on them
The only problem I have with these is i tend to forget to charge the little buggers up or the grandkids flatten them charging their phones/I pads.

Originally Posted by Wallyb

As for the connectors... Andersons 175A have a UL rating of 280A* .. what a coincidentally lovely number

Hi Wallyb and sorry mate but you are talking about a totally unrelated use. You are talking about a CONTINUOUS LOAD of 280 amps for a 175 amp Anderson plug.


As has already been pointed out, if you carry out a jump start correctly, you will actually be drawing only a part of the current required, from the DONNOR vehicle, to start the motor on the disabled vehicle.


I would be very surprised if it was as much as 150 amps coming from the DONNOR vehicle.


As such, being as a 50 amp Anderson plug can carry 220 amps for 1 second and 180 amps for 2 seconds, and 150 amps for 4 seconds, there is absolutely no harm done by using a 50 amp Anderson plug.


PLEASE NOTE, these are ANDERSON POWER CONNECTOR’S own specifications.

As I said before, my lithium jump starter does the job easily and is small enough to fit in my pocket. Why complicate it? No risk to my vehicle either.

Originally Posted by drivesafe

Hi Wallyb and sorry mate but you are talking about a totally unrelated use. You are talking about a CONTINUOUS LOAD of 280 amps for a 175 amp Anderson plug.


As has already been pointed out, if you carry out a jump start correctly, you will actually be drawing only a part of the current required, from the DONNOR vehicle, to start the motor on the disabled vehicle.


I would be very surprised if it was as much as 150 amps coming from the DONNOR vehicle.


As such, being as a 50 amp Anderson plug can carry 220 amps for 1 second and 180 amps for 2 seconds, and 150 amps for 4 seconds, there is absolutely no harm done by using a 50 amp Anderson plug.


PLEASE NOTE, these are ANDERSON POWER CONNECTOR’S own specifications.

As always Tim well put

these no longer need charging,,
NEW Ultra-Capacitor Jump Starter

Originally Posted by Pedro_The_Swift

these no longer need charging,,
NEW Ultra-Capacitor Jump Starter

What sort of cost are we looking at here?