Low voltage disconnect?

Electrical issues, both 12 volt and 120 volt

Low voltage disconnect?

Postby Sector9surf » Sun Feb 25, 2018 3:39 pm

Hi guys, I have a small project I'm working on and would like to get some input if anyone here is experienced in this. This project is on a Ford E350 van with only a single starting battery.

I'm planning on replacing my main car battery with a deep cycle battery so that I can run power directly off it when boon docking, but have concerns about over draining the battery. My understanding is I can drain the battery down quite a bit before it won't start my car, but don't know what the cutoff would be. Also, I'm running all things, mostly electronics and a box fan, through my cigarette lighters.(I'm trying to avoid full customization.

The first question is,

1. How far can I discharge my battery before it won't turn over the 5.4L v8 gas engine to start the car?
2. What can I install on my cigarette lighters to prevent over discharge?

I've found this...https://www.ebay.com/itm/12V-10A-Batter ... 3036539240 ...I'm not sure I'll be able to wire it through the cig. lighter hole without pulling out the dash... but might just use these if its not going to be too hard to install.

I'm also, considering just purchasing an inverter which has this built in and plugs directly into the cig outlet... The only thing is I'm mostly running 12v fans, to keep things cool and drown out noise when I'm sleeping, so only need the low voltage cutoff function which I can easily build in...

Any suggestions?
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Re: Low voltage disconnect?

Postby micabarry » Sun Feb 25, 2018 6:18 pm

What I have been told is that deep cycle batteries are not designed to give the burst of voltage needed to turn over an engine, but rather give a smaller amount over a longer period of time. It is possible to replace a deep cycle with a car battery for use in the van for lights, pump etc, but I don't think you would want to do the reverse. Better solution would be to find a place to install a 2nd, deep cycle battery.
I'm sure others will weigh in on this. Good luck with your project!
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Re: Low voltage disconnect?

Postby Kentuckian » Sun Feb 25, 2018 9:56 pm

You asked how far down you can drain the deep cycle battery and still have the ability to start the vehicle.

I don't know the answer to your specific question. However, I do have a fair amount of experience with deep cycle batteries and charging guidelines. Be aware that the greater percentage of drain you place on a deep cycle battery the shorter the life of the battery. The rule of thumb is to not drain lead acid deep cycle batteries more than 50% of its capacity. For a lead acid battery, 100% state of charge is about 12.7 volts. 50% state of charge is about 12.2 volts.

You should have no problem starting the engine at 12.2 volts.
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Re: Low voltage disconnect?

Postby micabarry » Wed Feb 28, 2018 1:45 pm

This is what I found by googling. Looks like it would work if unless t was real cold.
http://www.quora.com/can-you-use-a-mari ... y-in-a-car
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