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How can I wire it so that if my starting battery dies, I can flip a switch and use power from the rear bank to assist in starting the engine? Like this?
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To assist in starting, the switch would have to be able to safely carry hundreds of amps. The connection between the starting battery and the starter is a very heavy short wire for good reason.SunnyBoy 3000 US, 18 BP Solar 175B panels. -
Like this? The engine starts in less than one second... I built it myself. You turn the key and it goes vrooom
https://www.amazon.com/gp/product/B0...A2HJM3QFJ3LGZVComment
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SunnyBoy 3000 US, 18 BP Solar 175B panels.Comment
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And... is this even doable? What would the AWG of the line running to the rear battery bank have to be to account for a short burst of many amps for 1 second? It's a long line like 15 feet.Comment
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For the short time of a couple of seconds you can overload a wire significantly beyond its normal carrying capacity, since it will take some time to heat it up to the point where the insulation will be damaged.
To get significant help in supplying starting current though, you would need to keep the voltage drop on the wire down to 4V or less. If you can estimate the current drain of the starter motor and the length of the wire you can use tables or calculators to determine the needed wire size. One such is http://www.southwire.com/support/vol...calculator.htm
Plugging in the numbers to figure 20 feet of wire (one way, since we hope that the ground connection through the frame will be good enough to give a low voltage drop) and 200A and a voltage drop of 4V, we get a required size of #3/0 copper.
It will be difficult and expensive to run a wire that size through the vehicle, but fortunately you do not have to do that.
Instead of counting on the house battery to deliver the full current to the starter, a more practical solution would be to close the switch and let the house battery charge the starting battery for a few minutes and then try to start the engine. The current would then come mostly from the partially recharged starting battery.
This will only work if the starting battery is dead because it was discharged too far rather than because it has failed chemically or mechanically.
SunnyBoy 3000 US, 18 BP Solar 175B panels.Comment
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Simple you cannot. There is a reason SLI batteries are installed in the engine compartment close to the engine with large wires. You cannot remotely set a battery away from the engine. There is no wire large enough to carry 12 volts any distance.
What you can do is bypass the Isolator and have the House battery charge the SLI battery. Keep in mind a Deep Cycle battery is not made to crank an engine. Some can do it, but poorly at best.MSEE, PEComment
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That's not been my experience. I have a remote mounted starting battery on my Cummins powered Dodge truck, and many people relocate batteries aft for weight and balance considerations. It does require some serious cables. I have 2/0 welding cable and the drop is negligible.
I do run dedicated ground right to the starter mounting bolt and then the rest of the wiring connects from there up to the relays, etc. Where my cables used to end in a battery, now they go to remote jumping posts and shutoff switch.
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OK then, so I take it the smart way to do this instead of installing an expensive battery switch with large wire and actually bypassing the isolator would be to add a small toggle switch that controls the isolator?
Since the isolator needs 12v to make the connection between front and rear batteries then I need to run a small 12 AGW from the rear battery bank to a small toggle switch that when flipped turns on the isolator and makes the connection between the two battery banks.
Does that sound better?
And... if I left my lights on and drained the starting battery down to dead what might be a time frame on charging the starting battery like this? It is a good battery AGM DiehardLast edited by austexdude469; 10-23-2016, 01:57 PM.Comment
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You are in the right ballpark, but in the wrong section and way over thinking it. Not that difficult.
First you DO NOT want to automate it using a relay or switch of any kind. Much simpler. How would you jump a car with a dead battery? Would you buy switches and relays and hard wire to jump a car? Getting any ideas yet?
All you need is one Jumper Cable about 1 to 3 foot long. Connect one end to the SLI battery Positive Term Post first, ALWAYS FIRST. Then connect the other end to the Isolator terminal with the House Battery. Walk away for 10 minutes, start the vehicle. Disconnect the SLI Battery FIRST, then the other end and drive away.
Just beware when you connect to the Isolator, do so very quickly because you will draw a little fire. So open the jaws fully, and be quick about it. Once the jaws are tightly clamped on will make good connection and the sparks will quit flying. Once connected feel the wires and see if any are getting to hot for the first 30 seconds.MSEE, PEComment
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Do not know about you or anyone else, but I would not be caught dead without jumper cables in one of my vehicles. Heck I wear suspenders and a belt. I also carry a few MRI's, water, matches, gun, and a blanket in my vehicles. Saved my butt a couple of times. -
I try to be prepared myself. This van I'm building is partially for a trip I am taking around the country, and partially for piece of mind with the way things are going economically, politically, globally, and socially who knows where and when this crazy train is going to go derail but it's coming, and sooner rather than later. -
And yea... I got car jacked when I was 18. That won't be happening again. Not the kind of car jacked where he made me get out, the kind where he made me drive him someplace. I'd hate to have to splatter my new interior but the rounds I'm using at close range are not going to be pretty. Just thinking about that day probably raised my BP 10 points and it was 29 years ago.Last edited by austexdude469; 10-23-2016, 03:19 PM.
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That's ok... after all these years the red paint in her lips and black mascara around her eyes has bled out in into surrounding areas making her look like a 60 old crack freak with a bad makeup job, not to mention how thin the material has gotten in certain areas she could go at any moment.Comment
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