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  #1  
Old 12-02-2006, 10:01 AM
John John is offline
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Battery tech time

I'm adding a second battery to the Jeep, mounted in the rear (inside) under a tool box and behind the back seat. I'll use it for extra CCA on starting, to power the rear winch, and to run a power inverter off of it.

Now I get the crazy idea that if there's a 110 outlet in the Jeep then why couldn't I plug my engine block heater up to it? The rear battery is isolated unless the key is on, so it couldn't really hurt I figure.

Since the camper is in winter storage mode, has a perfectly good "deep cycle" battery that's charged up (camper stays plugged in to house) and a power inverter I figured to try a little experiment.

I unplugged the RV from the house so that the battery isn't being charged, I plugged the block heater to the inverter with the battery reading 13.5V and went back inside for 2 hours (hey, wind chill is around -20? or so) and then came back to see how it did.

The battery was down to 11.2V and the inverter wasn't powering the block heater any more, so it seems that it's a question of reserve capacity at this point. So now I'm on the prowl for a dry/gell cell battery that can handle this kind of drain. Anyone have any idea's on a battery up to this? Size isn't really all that much of an issue in this case either.
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Old 12-02-2006, 10:38 AM
Dan-H Dan-H is offline
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You need to do a little math, and the trick is to keep the units straight.

The capacity of the battery is likely measured in in amp-hours for a given voltage, say 12volts. I haven't researched batteries recently, but the numbers I recall are about 100 to 200 amp hours for a group 24 sized deep cycle battery. [edit] this might have been for a pair of batteries. It was for a bass boat trolling motor YMMV adjust the numbers once you find out the battery capacity.

Ok, if the reserve of the battery is 200 amp hours at 12 volts, then it can run a 12 volt, 1 amp load for 200 hours before it drops below 12 volts, or a 10 amp load for 20 hours etc. Simple math.


How efficient is your inverter? 90 % that needs to be factored in, but I'm going to ignore it for now.


How much power (watts) does your heater use?


400 watts = 3.32 Amps at 120 volts, or 33 amps at 12 volts.

if your inverter had zero power loss then you need 33 amps per hour to run the heater, or a battery with 330 reserve amps to run it for 10 hours.

If your inverter has 90% efficiency, then 10 hours drops to 9 hours.

If the battery only had 100 amp hours, then the zero loss inverter running a heater with a 200amp hour battery would run for 3.3 hours or about 3 hours if your inverter is 90%.

A 100 amp hour battery would last an hour an a half.

If the heater was 200 watss then its twice as long as the 400 watt heater.

Next steps ->

1) find out how many watts the engine block heater needs
2) find out the how efficient your inverter is.


from this you can calculate how many amps per hour it uses.

Then lookup specs on a battery ( for example: ) http://www.odysseyfactory.com/specs.htm

use the c/10 value and multply it by 10 to get the amp-hour capacity.
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Old 12-02-2006, 01:57 PM
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well I found out that is a 600 watt heater.
As for a battery, somebody was nice enough to point this one out

http://www.apexbattery.com/caterpill...dustrial-.html

but it might be overkill
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Old 12-02-2006, 07:52 PM
Dan-H Dan-H is offline
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Quote:
Originally posted by John
well I found out that is a 600 watt heater.
As for a battery, somebody was nice enough to point this one out

http://www.apexbattery.com/caterpill...dustrial-.html

but it might be overkill
if your inverter is 100 % efficient, that battery will run your heater for 4 hours.

An hour or two might be enough to warm the engine don't you think?
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Old 12-03-2006, 10:16 AM
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My goal is 2 hours
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Old 12-03-2006, 11:13 AM
Jerry Bransford Jerry Bransford is offline
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A real simple rule of thumb I use for how much something will draw from the battery through an inverter is 10X its 120 vac amperage draw and then add 15-20% to that for the inverter's non-perfect efficiency. 10X because it requires ten times the amperage at 12 volts as it does at 120 volts to do the same amount of work (watts).

So if something draws 6 amps at 120vac, it's going to draw 60+ amps at 12 volts. Then do the amp-hour calculation based on the battery's amp-hour rating and you can come up with a reasonably good estimate at how long the battery will last.
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Old 12-04-2006, 05:09 PM
Dan-H Dan-H is offline
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why not cut out the middle man. do they make 12volt block heaters?
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Old 12-05-2006, 08:41 AM
Rockjeep Rockjeep is offline
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I have my diesel plugged in to my garage on a timer. It comes on at 4:30am so when I leave at 7:00am the truck starts easy and heater is slightly warm. I have seen a 12v heater, but was not effective. We I was younger I use to spend alot of time in Loa utah with the brown brother construction co. My job was to start bon fires under the d-9 cats to warm the oil pan. You might try that.
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Old 12-05-2006, 08:46 AM
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Quote:
Originally posted by Rockjeep
I My job was to start bon fires under the d-9 cats to warm the oil pan.
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Old 12-06-2006, 09:41 AM
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There's no 12v heaters, so this is going to have to be as good as it gets. Even if I can only run it for an hour that's a lot better then nothing
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Old 12-06-2006, 10:19 AM
Rockjeep Rockjeep is offline
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Keep searching, you stopped to soon.
http://www.blueheatinfo.com/
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Old 12-06-2006, 10:24 AM
Rockjeep Rockjeep is offline
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With a little fabraction this will also work.
http://www.hydrogenappliances.com/hotwater.html
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Old 12-06-2006, 10:29 AM
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http://www.windturbine.ca/waterheat.html
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Old 12-06-2006, 10:36 AM
Rockjeep Rockjeep is offline
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I have found tons more and they can be adapted easy. 12 volt won't be as affective as 120volts, but it will do some good.
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Old 12-06-2006, 10:44 AM
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Blueheat I'd seen, but that's a propane powered heating system from what I saw. Now I never did think about the RV world of water heating though....
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Old 12-06-2006, 10:51 AM
Rockjeep Rockjeep is offline
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Not propane. It uses either diesel or gas. deponds on the vehical its going in. It uses the fuel for heat and 12 volts for the blower. Way cool.
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Old 12-06-2006, 01:58 PM
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OUCH

2. What is the cost of BlueHeat??

M.S.R.P. is $1,695 USD, installed.
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Old 12-06-2006, 02:36 PM
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heat isn't free.
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