truck battery back up system

truck battery back up system

Postby LostSkillsPodcast » Tue Sep 30, 2014 12:56 am

well i bought an inverter for the battery back up system i plan on putting in my truck. i got it at harbor freight for 129 bucks so we will see how it works out. it got really good reviews.
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i should be able to run most of my power tools from it. i will have it hooked up to 2 deep cycle batteries and mounted in my tool box. all i need now is a 30 amp solar charge controler to keep it charged up when the truck is running.
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Re: truck battery back up system

Postby LostSkillsPodcast » Tue Sep 30, 2014 1:32 am

here is a video of the battery backup system.
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Re: truck battery back up system

Postby Comrad » Tue Sep 30, 2014 9:45 pm

Very nice.

I'm actually not going to be a downer with this one. I think I have good news. I don't think you need a solar charge controller.

If you're running the two deep cycle batteries from your truck while the engine is running, that's all you need. Your alternator in your car already has a charge controller in it. Hence the reason you can hook up a multimeter to your engine while idling and its always around 13.4v. Solar charge controllers would only really be required if you were putting a PV system or some form of wind/hydro turbine on there.

You will need an isolator, though, preferably with the ability to have either battery, both battery, or no battery connected your alternator, as well as the option to have both batteries connected to the alternator system whilst isolating your trucks starter battery (for when you're not planning on going anywhere). I've seen mine site vehicles which have a pretty cool isolator switch for their batteries, similar to isolation switches on plant machinery. They can be switched off, and padlock put through them. Pretty nifty if you want to stop people from taking advantage of your battery bank.

Have you got the cabling yet? I always get smashed financially by the cabling. I reckon you'd want at least Gauge 2 AWG cable to deal with 2kW output, probably more if you routinely expect to hit 4kW surges (compressors and whatnot).

I'm keen to see how it turns out.
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Re: truck battery back up system

Postby LostSkillsPodcast » Fri Oct 03, 2014 3:51 am

The reason I am using a solar charge controller is 2 fold. The first reason is I can use a lighter gauge wire to connect the front to the back. The second is it will be a more intelligent charging system.monitoring the batteries charge and topping them off when necessary, Although the batteries will recharge slower I think that will better.
Also if I did it the regular way and depleted the batteries then started the truck the alternator will have to work harder to top off the batteries,a task which it is not designed to do for a long duration.

An alternator is designed to recover the battery after starting and then maintaining a partial load to keep the system running. Or at least that is what I have been lead to believe. From what i have heard people that plow snow a lot end up replacing alternator because of their pumps taxing the system. A plow pump draws a lot of amps to go up and down,side to side, which constantly drains the battery, making the alternator produce maximum amperage over extended periods causing premature failure.

but I could wrong this is just the line of thinking I was going with.

Jeff
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Re: truck battery back up system

Postby Comrad » Mon Oct 06, 2014 10:42 pm

I see your point. You're absolutely correct about the more intelligent charging and lower gauge wire.

I'd still recommend avoiding the solar charge controller though. I think something like a VSR would be more appropriate. If you get the right one, it can perform your isolation functions, charge control and cranking battery control. Having a charge controller where you limit your current in order to avoid larger cabling will mean that you get resistive losses going down through the controller, being less efficient and wasting energy in the form of heat.

Whilst drawing anything from a battery connected to a charge controlled commutator, you can assume the battery is simply a node. Current draw through the battery will be matched by a power input from the commutator, so you're still going to be drawing from the alternator.

You can simply run off the batteries as their own power sources, and then charge them at a constant rate, like drawing from a water tank which is being filled by a thin outlet float valve, but even true deep cycle batteries don't love being fully discharged. They certainly handle is better than a cranking battery, but if you let it discharge regularly (which a 2/4 KVA inverter will easily do when running decent power tools) you'll wreck your batteries. A 30 amp controller will be equivalent to a 360 VA supply. Depending on the capacity of your deep cycle batteries, you could wear them down fairly quickly if you were using things like welders, compressors, angle grinders, circular saws, etc...

I'm not trying to be a bummer. I've just done a lot of this stuff before, and I've had a lot of things not work in the past. They're expensive lessons. I just wanted to give you some things to think about before you spend your money.
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