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Old 07-09-2019, 07:02 PM   #1
russinthecascades
 
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Default Jumping starter battery from battery bank

By varying ways we've managed to drain our starter battery a couple of times. Yes, I know it's really bad for the battery.... The last time it happened we were at a Santana concert, so lots of folks around and got a jump from a sheriff. It got me thinking of an emergency plan....

My house system is 4 100 Ah AGM batteries completely isolated from the vehicle electronics. I was thinking of making some custom jumper cables to span the distance. Then turn off the solar controller and inverter/charger, and jump from the most + positive pole and most - negative pool. Hooking directly to the batteries would by pass all fuses and switches.

Will this work? Am I putting any components at risk? Emergency use only - think way out of cell range and no other vehicles around. TIA
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Old 07-09-2019, 07:07 PM   #2
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Default Re: Jumping starter battery from battery bank

I use an automatic charge relay (ACR) between house & chassis banks. I can manually open or close it, and this allows me to start the vehicle from the house bank. I believe starting the van requires ~100-150A weather dependent, and this is not enough to damage your house bank.
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Old 07-09-2019, 07:17 PM   #3
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Default Re: Jumping starter battery from battery bank

A trick to remember in cases like this is to join the batteries ... and then wait a few minutes .... this allows a partial re-charge of the Starter battery *before* trying to start the van... that will be that much less current that will be asked to flow through the "jumper" during the starting process.

Many people have such an "over-rideable" isolation relay/gadget for just this situation.
There should be no need to disconnect your solar (etc), it'll just think your house battery is (momentarily) at a very low state of charge.

--dick (who'll get around to installing such an isolator ... some day)
(at the moment i carry jumper cables)(and a shore-powered "can supply short burst of 125 amp starting current" battery charger)
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Old 07-09-2019, 07:30 PM   #4
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Default Re: Jumping starter battery from battery bank

Quote:
Originally Posted by autostaretx View Post
A trick to remember in cases like this is to join the batteries ... and then wait a few minutes .... this allows a partial re-charge of the Starter battery *before* trying to start the van... that will be that much less current that will be asked to flow through the "jumper" during the starting process.

Many people have such an "over-rideable" isolation relay/gadget for just this situation.
There should be no need to disconnect your solar (etc), it'll just think your house battery is (momentarily) at a very low state of charge.

--dick (who'll get around to installing such an isolator ... some day)
(at the moment i carry jumper cables)(and a shore-powered "can supply short burst of 125 amp starting current" battery charger)
I did exactly that, using the original battery isolation relay, controlled manually by a big red guarded switch, just for effect. The normal charging from the starter battery to the house batteries is via a Sterling BB1260, round control panel on the right. Solar is the control panel on top. Inverter / Charger is the control panel in the middle. Big red scary looking switch on the left is to charge the starter battery from the house batteries. Takes maybe 10 min or less to provide a charge enough to start the vehicle.

Control_Panels.jpg

Regards,

Mark
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Old 07-09-2019, 08:29 PM   #5
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Default Re: Jumping starter battery from battery bank

Just know if the problem is a dead short rather than just a depleted Starter, you may create more problems.

An alternative is those pocket sized lithium jumpstarter packs.
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Old 07-09-2019, 08:39 PM   #6
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Default Re: Jumping starter battery from battery bank

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Originally Posted by john61ct View Post
Just know if the problem is a dead short rather than just a depleted Starter, you may create more problems.

An alternative is those pocket sized lithium jumpstarter packs.
I have a resettable breaker in the line, I think 30A, for that case, and the wiring is not that large.

Regards,

Mark
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Old 07-09-2019, 11:50 PM   #7
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Default Re: Jumping starter battery from battery bank

Cranking an engine can easily be 500+ amps, but for a short time.

The infrastructure between House, ACR, from there to Starter needs to handle that safely.
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Old 07-10-2019, 12:19 AM   #8
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Default Re: Jumping starter battery from battery bank

Quote:
Originally Posted by john61ct View Post
Cranking an engine can easily be 500+ amps, but for a short time.

The infrastructure between House, ACR, from there to Starter needs to handle that safely.
Define short time.....
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Old 07-10-2019, 01:43 AM   #9
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Default Re: Jumping starter battery from battery bank

Calbiker logged a few start cycles. After a few ms, the sprinters starter is less than 200A. I think 125A was the sustained number.
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Old 07-10-2019, 01:53 AM   #10
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Default Re: Jumping starter battery from battery bank

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Originally Posted by OrioN View Post
Define short time.....
Well for a healthy rig the overall event shouldn't be much over a second.

But the really crazy high current levels are only for the first 50ms or so, then dropping by half in each of the next 50ms units, as inertial resistance / friction is overcome and the crankshaft starts actually rotating.
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