# Help with figuring Batteries Needed using an inverter for my AC Floundering Lights



## timhardison (Jan 1, 2014)

I have 4- 500 watt halogen lights on the front of my boat that I currently use with an electric generator. Although I have tried to read online how to calculate the amp hours needed, this all sounds like greek to me. I would like to consider and inverter to use with batteries. I had two electrical fires last year on my boat, and I want to get away from using the electric generator. I know that LED lights would use less current, but from all the flounder fishermen I have talked to, they really don't penetrate the water as well as my 500 watt halogens do. I don't know if I am wasting my time trying to use batteries to supply this much current, or whether mathematically it is possible or even feasible. I normally may need lights 8 hours or so a night. I already have 3 deep cycle batteries, but have no idea how may amp hours each are rated. I would need advice on what type of inverter would be needed, if this is even possible. I know there are those that give 2000 watts continuous or 4000 peak, and 3000 continuous and 6000 peak, but I really don't know which would be best, or if it would just take too many 12 volt batteries in my boat to even consider doing something like this. If anyone could give any advice, or just tell me it is not worth doing I would appreciate some expert opinions or advice.


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## mellowhead (Mar 29, 2014)

A group 24 deep cycle battery holds roughly 1kWh, so at a 2kW rate for 8 hours, you would need minimum 16 of those batteries. To attain maximum value from lead-acid batteries, the general rule of thumb is a maximum of 50% depth of discharge, so factoring that in brings you to 32 of those batteries, or any 12V, 32kWh battery configuration. If you are going to invest in a battery bank that large, there are better ways to spend your money than with 12V marine or deep cycle batteries. PM me if you decide to go that way, I'm a bit of an expert on them and exclusively sell batteries/inverters/solar products at my day job.

Cheers,
Jeremy


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## RetroTechie (Mar 29, 2014)

For starters: Watts = Volts x Ampères. Wh = Watts x hours. For example a 12V, 55Ah battery holds energy to power a 12V, 1A load (= 12W) for 55 hours. Or a 12V, 55A load (= 660W) for 1 hour. Or anything in between. An inverter should not change much as they (especially high power ones) are pretty efficient. Read: _roughly_, power in = power out. Just collect the numbers, multiply and divide (and watch your units!).

Of course that's theory. You'll need (possibly big) margins as to not cycle batteries too deep.



timhardison said:


> I know that LED lights would use less current, but from all the flounder fishermen I have talked to, they really don't penetrate the water as well as my 500 watt halogens do.


I'd start there, and do some actual testing. For example get some different LED light sources (perhaps some single-color ones red/green/blue), and see for yourself which colors best go where you want the light to end up, and how useful the result is. 4x 500W is a lot of power for lighting, which means if you can cut that down, you can also reduce the energy storage + conversion requirements by *a lot*. And the corresponding costs as well. 



mellowhead said:


> If you are going to invest in a battery bank that large, there are better ways to spend your money than with 12V marine or deep cycle batteries.


+1

Another example: I saw some methanol-powered fuel cell generators (for boat / caravan use etc) a while ago. Pretty expensive IIRC, but perhaps prices have come down enough to make such things suitable in your case. There must be other solutions like that out there.


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## turbodog (Mar 29, 2014)

Blend the halogens with some high-power led units to bring total power usage down while still keeping good penetration. Then, run the whole thing from a honda eu2000i generator. It's quiet, , lightweight, very fuel-efficient, and will pay for itself in fuel savings quickly.

Referencing post #2... yup. You need a LOT of expensive, heavy, batteries to even think of running those lights. Then you've got to charge them.


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