Advice on charging deep cycle from car...

[kayakrguy]

Hi folks,

I am weighing alternatives for charging my trailer battery when I don't have hookups. I know I can get a generator as one alternative. BUT the $$$ cost of a decent one is kinda heavy for the pocketbook. Plus there is the added weight, space etc etc...

So, I know that some folks charge their TD batteries from their car alternators. I would appreciate the +'s and -'s of that arrangement. Its complexity. COST, and best places to get it done...

In some ways, the charging from vehicle thing looks attractive/cost effective but I realize there is a downside to everything....???

Thanks, and I hope all is well with everyone!

Jim

[Dale M.]

Well the expense would be the cost of installing the wiring and or updating plugs on trailer/car connection.... And the cost of fuel of just "idling" T.V. in camp vs. "on the road" charging...

The upside, is you will not be in the dark.........

I can't see any real negative and can't imagine not having this capabilities for any camping situation. Specially on long trips where facilities may not be most convenient ........

Dale

[brian_bp]

... And the cost of fuel of just "idling" T.V. in camp vs. "on the road" charging...

I don't think many people idle just to recharge. The usual idea is that the trailer battery charges while driving between sites (the "on the road" part), so a long stay in one site means a large battery or a supplementary charging plan (such as solar, or a generator).

[brian_bp]

...I can't see any real negative and can't imagine not having this capabilities for any camping situation. Specially on long trips where facilities may not be most convenient ........

Dale

I agree. Even if it is not the only charging method, or even the primary method, it makes sense to take advantage of the tow vehicle's capability.

[Lou Park]

But doesn't a deep cycle battery take quite a bit of time to charge?
What will happen to it, if it's charged for an hour here and there?
Lou

[Dale M.]

... And the cost of fuel of just "idling" T.V. in camp vs. "on the road" charging...

I don't think many people idle just to recharge. The usual idea is that the trailer battery charges while driving between sites (the "on the road" part), so a long stay in one site means a large battery or a supplementary charging plan (such as solar, or a generator).

Isn't your tow vehicle technically a "generator" when charging a battery.... Besides auto alternator has probable a lot higher amperage ouytput than small generator...

Dale

[Dale M.]

But doesn't a deep cycle battery take quite a bit of time to charge?
What will happen to it, if it's charged for an hour here and there?
Lou

Actual charging question probable can be answered at this site....

http://www.batteryfaq.org/

Dale

[Gerdo]

My TV is setup to charge my TD battery. I have a master kill switch on my TD battery so if I don't want to charge it I just turn it off. This keeps it from getting a bunch of short charges. If the battery is low then I can turn it on for a long drive and fully charge it. It is the same switch that disconnects the TD battery from the cabin power.

[kayakrguy]

Gerdo, Dale, Brian,

Thanks for your repliesw...

I have a couple of questions and hope your experience can provide some input...

Looking at Honda generators, the 1000i puts out about 7.5 amps and the 2000i puts out about 33.5 amps....that is, I assume in AC output.
Not shure what that converts to for 12 v input for charging power? Any idea?

Also what is the amperage output of the average 12v alternator on a 4 cyl car/

What I'm trying to get a handle on is charging times of generators vs alternators re: effieciency/fuel use wear and tear on catalytic converter etc...

Thanks,

Jim

[G-force]

the 2000i does not put out 33 amps, more like 16 or so amps at 110v AC. I believe both the 1000i and 20001 have a built in, 12v , 8 amp charging system.

[kayakrguy]

My goof--I meant to type 13.5, not 33.5!!!!

[Sonetpro]

My Honda has 12V output but I would not use it to charge a battery. It is unregulated. So if you are charging and when the battery is charged it will continue to charge it and cook it.

[brian_bp]

... And the cost of fuel of just "idling" T.V. in camp vs. "on the road" charging...

I don't think many people idle just to recharge. The usual idea is that the trailer battery charges while driving between sites (the "on the road" part), so a long stay in one site means a large battery or a supplementary charging plan (such as solar, or a generator).

Isn't your tow vehicle technically a "generator" when charging a battery.... Besides auto alternator has probable a lot higher amperage ouytput than small generator...

Dale

Yes, but it's a huge engine to run for this purpose, and the alternator output at idle is not great... nothing like the dozens (or up to a couple hundred) amps it can do at normal operating speeds. Mostly, it's burning gas to overcome its own internal friction and pumping losses.

If you are just running a generator to charge a battery (not, for instance, to run an air conditioner at the same time), the smallest generator you can buy will be lots for as much charging rate as a small trailer's deep-cycle battery will want.

[brian_bp]

Looking at Honda generators, the 1000i puts out about 7.5 amps and the 2000i puts out about 33.5 amps....that is, I assume in AC output.
Not shure what that converts to for 12 v input for charging power? Any idea?

Also what is the amperage output of the average 12v alternator on a 4 cyl car...

The maximum AC current output of either of these models is far higher than you would need to run any reasonable battery charger... and running a charger from 120V AC is the way to charge the trailer battery. The only advantage of a larger generator (if it is to do nothing but charge the trailer battery) is that in advanced designs (such as these Hondas), the engine only runs as fast as it needs to, so for the same load the larger unit will run more slowly, and thus more quietly and efficiently.

They do have DC outputs, but as Sonetpro mentioned, it is not properly regulated for battery charging and that's not the recommended way to charge the trailer battery.

My old Toyota Tercel had a 35-amp alternator, and for all I know they could be twice that now (cars are stuffed full of more electrical stuff every year)... but that's at normal operating speed. At idle, I have no idea... they may not put out anything significant at the voltage needed to fully charge a battery. I suspect that in some cases starting the car and connecting the discharged trailer battery will mostly a matter of the car battery transferring its charge to the trailer battery. I suppose most cars could be tricked to running at fast idle for better charging, and it may be worth doing that to avoid the need for a generator.

[Dale M.]

A simplistic approach to battery charging is a simple convert by 10.

If a battery charger is capable of 25 amp out put at 12 volts it will require about 2.5 amps 110volt AC side.... 25/10=2.5

Flip side is if a battery charge draws 1 amp on 110volt AC side, its 12volt DC output will be about 10 amps.... 1x10=10

As you lower line voltage, current goes up.... If you raise line voltage current goes down.. When converting to a different voltage... BUT it only works if the current is a set value on at least one side of equation....

IF you want to convert watts to amperage...

Watts / Voltage = Amps

So a generator out putting 120volts and capable of 3000 watts....

Watts / Volts = Amps

3000/120=25

So generator is capable of about a 25 amp load....

To go other way 25 amps at 120 volts ..

Amps X Volts = Watts

25 X 120 = 3000

Remember these calculations are "ball park" figures, but can get you close enough....

Here is a site that may help with the voodoo....

http://www.sengpielaudio.com/calculator-ohm.htm

Dale