power inverter / watts?

bassdog · June 14, 2002

Ok all you engineers, electricians, RV'ers and such, I'm in need of some help.

I need to purchase a power inverter to run a battery charger (12A) to keep my boat batteries charged the week I am on vacation. There are no electrical hook-ups at the campground so I need a 12VDC - 110VAC converter.

How many watts do I need to run a regular battery charger?

Thanks!!!

Cyclic · June 15, 2002

I'd actually go with a solar type charger. No mess, no fuss, no running down your vehicle battery. You get alot of loss by going 12V to 110V and back to 12V. Another method is to use the RV power connection part of the hitch to charge the batteries but only while the truck is running. Does you boat have a gas motor? Another option is to make your own 12V charging system........... very simple to make and pretty cheap. Use a lawn mower engine ( or any other 2 to 8 horse power motor) bolted to a plate, connect to a chevy one wire alternator by a v-belt. Bingo instant 12V charging system. E-mail me if you have any questions. ;)

JonesNTN · June 15, 2002

Well its been awhile since studied this sort of thing, and icoud be WAY wrong, but using the formula P =I X E, (110 X 12 = 1320) It looks to me like you need atleast 1.4 kw to even operate. To safely operate, it would seem you would need at least 2kw, and possibly even more if you plan on using this for other things also. I could be wrong, maybe someone knows more?

MarkD · June 15, 2002

JonesNTN,

I think you may be using the equation improperly...(no offense intended)

P= I x E

Power (watts) = voltage x current

your equation would read 12 amps at 110 volts = 1320 watts

12 amps of 110 voltage is quite a substantial amount.

by comparison 110 amps of current at 12 volts =1320 watts (the same). You could do some welding with that much current.

A 300 watt inverter is what I use at our plant to run the battery chargers that charge the 12 volt batteries on our mobile digital scales.

JonesNTN · June 15, 2002

I do believe I am wrong after thinking about this a bit, and I have absolutely no idea what you need, sorry bro. Good Luck.

bassdog · June 15, 2002

Thanks guys, 300W sounds like all I need. Cyclic - I have a 90HP motor for the boat, and yes it does charge the cranking battery, but not the trolling battery.

Now, I heard something about a modified sine wave? How does this effect the charger?

Thanks

WEFs99 · June 15, 2002

Add a marine (spark proof) battery switch between your cranking battery and the trolling battery. Late model outboards alternators are big enough to recharge pretty fast.

Cyclic · June 16, 2002

I agree add either a battery switch or better yet try a battery isolator. Almost all parts places carry a battery isolator. Bolt in affair and they are sealed with a built in heat sink. Simplist and cheapest way to go for your set up. Later.