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bemis

join:2008-07-18
Reading, MA
Reviews:
·Comcast

two batteries temporarily...

Hypothetical question while we're in snowpocolypse in the new england area--

I have a large marine battery and a 2000W inverter which I have used in the past to run a few times in the house.

If I needed to extend the run-time with that battery, would it be acceptable to connect the marine battery to my car battery via jumper cables while the engine is running at fast idle?

I know that it's not OK to simply connect to two batteries permanently because the weaker will end up discharging into the other, but I assume that with the engine running and the alternator keeping the terminals of both batteries into the 14V range, that this issue will not be present?



shdesigns
Powered By Infinite Improbabilty Drive
Premium
join:2000-12-01
Stone Mountain, GA

Paralleled bats is fine, one will not discharge the other, they will equalize a bit.

It should work but will be hard on the alternator. Being cold out it should not be bad. Hot day, car idling and heavy load is the worst.


bemis

join:2008-07-18
Reading, MA

Hopefully will not need it--I have a generator and anyway my power hasn't gone out... but I after that ice storm in 2008/2009 I'm keeping as much as I can in my back pocket.



Rifleman
Premium
join:2004-02-09
p1a

I had 4 marine batteries as well as the engine battery in my RV. I never had problems charging them off the engine.


bemis

join:2008-07-18
Reading, MA
Reviews:
·Comcast

said by Rifleman:

I had 4 marine batteries as well as the engine battery in my RV. I never had problems charging them off the engine.

Wouldn't you have had an isolator setup in an RV tho?


Rifleman
Premium
join:2004-02-09
p1a

The isolator only kept the engine battery from becoming discharge when using the house batteries. The 4 marine batteries were wired parallel in the battery box--and running the engine chaged the house as well as the engine battery.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7
reply to bemis

said by bemis:

I have a large marine battery and a 2000W inverter which I have used in the past to run a few times in the house.

If I needed to extend the run-time with that battery, would it be acceptable to connect the marine battery to my car battery via jumper cables while the engine is running at fast idle?

Just remember, the car is going to recharge slower then what you'd likely be using. A car's alternator may not be that powerful. Not accounting for any current the car needs to run, or inefficiencies of the inversion process, a 150amp alternator will only get you 15 amps of power at 120v. If you're using more than 15 amps, then you'll be recharging it for just as long as you use whatever is plugged into it. And that's with a 150amp alternator. Alternators 1/2 that size aren't uncommon, so you could be recharging two hours for every hour of use (not including inefficiencies).


Rifleman
Premium
join:2004-02-09
p1a
reply to bemis

Yeah----a 2000 watt inverter at 120 volts will pull 166 amps roughly from the batteries. You'd need to size your wire accordingly. I think it would be 2/0 and the batteries will die in very short time.


bemis

join:2008-07-18
Reading, MA
Reviews:
·Comcast
reply to bemis

I'm not maxing the inverter by any means, my boiler users 400-600W with one zone circulator running and the boiler firing. That's all I'm running...

I've got a wee little 2003 Civic which is just a 70A alternator, so yeah not thinking I'll do much other than be able to charge the big battery for a couple of hours by fast idling.



mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

2 edits
reply to Rifleman

said by Rifleman:

Yeah----a 2000 watt inverter at 120 volts will pull 166 amps roughly from the batteries. You'd need to size your wire accordingly. I think it would be 2/0 and the batteries will die in very short time.

Whoa--whoa there fellas!

OK----removed for now.


Rifleman
Premium
join:2004-02-09
p1a

2 edits

I don't think you're correct on that. I couldn't run a 12 volt fridge at 10 amps for more than 5-6 hours on one house battery.
I had a 3000 watt inverter and if it was only pulling 15---20 amps I should have been able to run a 120 volt microwave or air conditioner off the house batteries for a few hours---but no way it would happen. With the engine idling it couldn't supply 2000 watts at 120 volts without a deficit.
Here's an inverter kit with 300 amp fuse
»www.theinverterstore.com/3000-wa···kit.html



mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3

OK withdrew that---

I know there's an explanation--- You may be right on the higher-draw stuff, I think the inverters I put in were smaller than 2000. But there is a difference in draw from the DC-AC conversion, and I can't come up with what it is.



Rifleman
Premium
join:2004-02-09
p1a

I just used a basic formula of watts/volts=amps.


bemis

join:2008-07-18
Reading, MA
Reviews:
·Comcast
reply to bemis

Yes...

P=IV and I=P/V

I = current (amps)
P = power (watts)
V = voltage

In this case 2000W/120V=16.6A at the output side or 2000W/12V=166A at the input side. Power is comparable at either end, because it represents a relationship between voltage/current.

Of course the conversion by the inverter is not nearly 100% efficient, but that's not really the point. The general idea is that for each amp you need at household voltage you should expect to pay at least 10A at automotive voltage.

Mostly my worry was whether--from a practical point of view--connecting two batteries in parallel would be an issue, it sounds like it generally will not be.



DeltaElite
We Dont Dial 911

join:2002-03-29
Tucker, GA
kudos:1
reply to bemis

What ya'll are failing to mention is the RV has a 230 watt Alternator.....Most cars and trucks dont have near that kind of charge capacity.

I'd hook the marine battery up....Eye ball the entire rig while it was hooked up AND leave the vehicle running so as not to cause a large draw on the cars charging system...

Burning wires and alternators stink.
--
Protect your right to keep and arm bears!



Rifleman
Premium
join:2004-02-09
p1a

The batteries supply the amperage and act as a sort of capacitor. As song as the batteries are fully charged to start the honda will be fine. Sooner or later at 2000 watts he'd probably damage the alternator but he's running 600 or so and the alternator should easily keep pace.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7
reply to DeltaElite

said by DeltaElite:

What ya'll are failing to mention is the RV has a 230 watt Alternator.....Most cars and trucks dont have near that kind of charge capacity.

Every single car I've ever owned had an alternator larger than 230 watts. I think the little "generator" I had as a kid on my bike that powered the headlight was around 230 watts....


Hagar

join:2004-10-31
Sunnyvale, CA
Reviews:
·T-Mobile US
·AT&T U-Verse

said by DeltaElite:

I think the little "generator" I had as a kid on my bike that powered the headlight was around 230 watts....

I think not, an average person will be hard pressed to generates 250 Watt for more than 20 min. A old bike generator was probably 25 Watts.

Note the watt your exercise machine report is what your burn but we are not very efficient so we generate much less useful energy most of it becomes heat.


Rifleman
Premium
join:2004-02-09
p1a
reply to DeltaElite

He meant amps--not watts



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

1 recommendation

reply to Hagar

said by Hagar:

I think not, an average person will be hard pressed to generates 250 Watt for more than 20 min. A old bike generator was probably 25 Watts.

It was a bad attempt at humor, hence the smiley. I forgot people are humorless here.


Hagar

join:2004-10-31
Sunnyvale, CA

My bad, sarcasm detector was working but not humor detector.

I did not even see the smiley