jfpointer

I'm trying to decide whether this is workable or not. I came into possession of a couple of deep-cycle batteries from a UPS system that my employer decided to replace with a newer model. I've also got a huge truck box, and can't plug in during the day when I'm at work.

So here's the idea: mount one of the batteries in the box along with an inverter of a size appropriate to provide sufficient power to the block heater. During the day when I'm parked at work, plug my block heater in to this inverter. At night, when the truck's parked in the garage, plug in a trickle charger to recharge the deep-cycle. I normally leave the office at lunch, so the block heater would be running off the battery for around three or four hours at a time, and the battery would generally have at least ten hours at night to recharge.

Crazy, or $80 well-spent to have the truck keep warm during the cold winter days?

infidel

My bet is the batteries wouldn't run the block heater for more than an hour if that.

10HAAP

Ditto, and a trickle charger would no where near restore the charge in 10 hours.

Steve

P.J

But aren't the batteries intended to run a server in a power outage? Question would be how many watts can a single battery uphold for X amount of hours?
How about just being able to flip a switch an hour or so in advance of when you need to start the truck? What size inverter were you thinking? The grid heater is what, 800watts?

CTD NUT

800 watts @ 12v is a 66.6 amp draw and tack a few more amps on that for the correction factor when running the inverter. You would need some massive battery power to sustain that load for any length of time and a very powerful charger to charge that bank of batteries with a total amp/hr rating high enough to sustain that load in 10 hours. It could be done but at what cost?

P.J

Wowzer, 66+ amps?

Uh oh.

WideOpenThrottl

I think it would work to warm your block up, but it will drain the batteries pretty fast i would assume, but you have to remember you only need to have the block heater on for about 45min to an hour for the block to be up to temps, at least thats what my manual says.
And instead of trickle charging them, have a heavy battery cable with a breaker type shut off so you can charge them with the trucks alternator on your drive to and from work, the disconnect it at work so it does not drain your under the hood batteries.
I thinks its a good idea, well worth a try IMO., i had thought about the same idea a while back, but too much $$ to buy extra batteries, but you already have them so give it a try.

jfpointer

Thanks for all the input, guys. If I remember correctly, the block heater is about 700 watts, so 800 watt inverter. 700/12=58, so about a 60 amp draw. I think my flaw was calculating the current draw at 120v and forgetting to multiply by 10 for the 12v side.

I'm hesitant to hook it up to the truck's charging system for the simple fact that it would mean more expense to isolate them from the other batteries and a more complicated wiring job as well, plus my drive to work is slightly less than 5 miles, so I'm pretty sure they wouldn't have sufficient time to recharge anyway.

It still seems like it might be doable if I: 1. Plug it in/turn it on about an hour before I leave; and 2. Get a serious enough charger to hook it up to at night.

Number 1 is not too big a problem; it actually doesn't cool that much between when I arrive at work and when I normally leave for lunch. In the evening, though, it's been sitting there for 4 or 5 hours as the temp drops, so it would be more helpful then.

I might give it a shot, but I have plenty of other projects that'll take precedence over it. Air horn, for one. I have many idiots to inform of such.

Boatnik

I have a friend that came up with this idea. Install an onboard battery charger and an inverter. Plug the battery charger into the inverter too maintain the battery. For a welder, that ain't to bad.

jfpointer

If only that would work! Has he figured out how to make gold out of lead yet?

infidel

The way a fellow I know takes care of this situation is with a little lunch box sized gas generator. It runs all day on a half gallon of gas.
Of course he parks in the boonies where no one will steal the generator...

Clunk

2 battery chargers would charge it twice as fast

Jc9995

its do-able... but heres the problem. Those batteries you have are pretty small. Most likely 7-10 AH (ampere hours). Which means they have the equivelent of 1 amp draw for 7 hours, 7 amps for 1 hour, ar any variant in between.
Inverters are about 93% efficient. So lets say you get an 800 watt inverter. Thats 68 amps. To run it for 1 hour, you need at least an 85 AH battery. Then to charge, you will need at least 4 hours at 20 amps. BTW, 20 amp charge rate is fairly high, definatly NOT trickle charge. Also, Inverters consume about 1 amp at idle. So you will need to disconnect it while not in use.
Car batteries (like in your truck) are 750 Ah. So this is do-able, just probably not with your batteries from the UPS.
FWIW. Its a good thought though. I wouldnt mind doing it. although, My drive is about 45 minutes each way, so I have the benefit of just charging the battery with the truck charging system.

slim51015

How cold does it get where your at?I could leave my truck sit 9 hours in 0-10 degrees and cycle the grid heaters once and it pops right off.

Shovelhead

Maybe just find a parking space next to a Toyota Prius and come up with an adapter to plug into their battery system...........