Inverter & Large Battery Bank Questions

nicholasbw

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24 Feb 2005
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Bear, DE USA
I’m attempting to engineer a battery supply capable of producing 20amps, 120Volts for a period of 24 hours.

Is 12v, 24v or 48v better?
Any Ideas on a tried and true inverter?
Any Ideas on a high output Alternator?

Thanks in Advance…
 

davel

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The required battery bank will probably sink your boat!!
Even without allowing for inefficient inverters the simple maths shows you'd need approx 5000Ah capacity, double that to allow for batteris not discharging fully and you'd have one hundred 100Ah batteries !!

I'm intrigued as to why you need that much power from a battery bank?
 
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Anonymous

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You are asking for a 2.4kW supply for 24 hrs which is the output of a small diesel generator. Assuming you don't discharge much below 50% then the approximate weight of your battery to provide 58kWh will be around 2800kg regardless of the voltage. At 12V, you will be discharging at 200A, at 24V, 100A and at 48V you will be discharging at 50A. The wiring, fuses and switchgear will all be much lighter, cheaper, and easier to handle the higher the voltage.

I'm not sure that batteries are a sensible solution for your power needs unless there is some unusual constraint (e.g. you are a submarine /forums/images/graemlins/smile.gif) or need to operate with a minimum of noise and smell - though some gensets are very quiet and can be silenced very well if you are prepared to pay for that to be done.

As for cost, if you go for top of the market sealed lead acid, you would be paying around £20,000 for your batteries. If you go for good branded flooded lead acid, you will be paying around £10,000.

I hope that's of some use?
 

nicholasbw

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Actually I was planning on offsetting the load with an oversized Alternator...

Is a 200 amp Alternator a common practice?
 
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Anonymous

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[ QUOTE ]
Well reducing the requirements to 6 hours and relying on an oversized alternator...what would you recommend?

[/ QUOTE ]You enter a new realm of problems. When you asked for discharge over 24hrs you were working at lower than the '20 hour rate' so you would have got the quoted Ah capacity for the batteries. If you are going to discharge over only 6 hours you will get very much less than the quoted capacity. There is no point in any of us 'sharpening our pencils' to give you exact figures for such a large system. You should be talking to the projects department of a major battery or charger supplier. Talk to Mastervolt, Exide or Varta.

As for oversized alternators, you are asking for a 2.4kW load. That's over 3hp. You would need at least a double belt and there would be implications for the alternator bracket, and the water pump pulley. It feels wrong to me.....2.4kW for 6 hours is generator territory and if you are going to run your main engine anyway, what's the problem?

But please satisfy my curiosity. What do you want the 2.4kW for? If it is heat, have you considered using the engine's fresh water cooling circuit? It's a heck of a lot of power to be using for such a long time.
 

nicholasbw

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AC & Ice Maker for the southern latitudes, other not load demainging items also. Grand total is just a little under 20 amps.

Thanks so much...
 

ytd

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13 Jan 2005
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Once you mention air con you are talking a generator. They have high starting loads and will trip inverters well above the rated wattage. If the inbuilt diesel option is too pricey, lots of boats (and vans) here just put a petrol powered gen on the deck when they want to run the AC. Hondas are particularly quiet. The AC will make more noise.
 

William_H

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Just a few comments re some of the details but overall it sounds like madness. High current 24 volt generators (alternators) are made for aircraft so go to a light aircraft electrical service. Yes multiple belts etc.
An inverter for high current should run on the highest voltage ie 48 volts assuming you can get a 48v inverter and generator to suit.
If you are talking airconditioning then you would be far better to run a compressor off an engine (auto aircon) with sea water cooling of the condensor with huge improvement in efficiencies. same refrigeration and icemaker. I reckon engine and compressor would be quieter than a domestic type aircon unit. Or a 120 VAC alternator engine driven. No I don't think batteries would see you through a night in practice. Could have used aircon on the boat last week as mercury hit 42 degrees. Too hot for sailing. ( son lives about 4 hours up the road they hit 47 degrees. better than snow. regards olewill
 

Graham_Wright

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Re: Inverter & Large Battery Bank Questions

There was considerable discussion while back on motor vehicle AC conversions.
Look under my posting name for car heaters.
 
A

Anonymous

Guest
[ QUOTE ]
AC & Ice Maker for the southern latitudes, other not load demainging items also. Grand total is just a little under 20 amps.

[/ QUOTE ]The actual capacity of deep discharge batteries declines over their life; you are talking about using this on a daily basis and your batteries, quite aside from being huge, heavy and expensive, will not last for long before you need to replace them. This is not the right way of going about it. If you are going to the southern latitudes you will also want a watermaker, I suspect? If you want AC and an icemaker, you will have a washing machine and expect to have regular showers? It seems to me that you need a proper fixed diesel generator; I cannot see any other practical way of getting the lifestyle you are looking for.
 

Sea Devil

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Boulogne sur mer & Marbella Spain
Re: Inverter & Large Battery Bank Questions

Just on a practical cruising note - nearly all blue water cruisers spend at least 85% of the time either on anchorage or in marinas. The marina will always have a powersupply. When on anchorage bigger yachts run generators - silent ones.

I have spent some time in the tropics in my boat. On anchorage,except in a few places, there is always a breeze and life is very pleasant without air con. When you are on the move more so - air con is not really required.

In a marina air con is a must - no wind - no breeze - hot as hell.

Ice will make itself when you are on mains power easily - when you sail off during the 10-15% of the time you actually voyage the ice should keep in the fridge for long enough to reach the next port and start the generator - plug into mains.

The above all assumes you have slightly less than a gin palace or an overall length of say 50ft...
 

boatmike

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Solent
Re: Inverter & Large Battery Bank Questions

The sum total of all this advice is that if you want to run aircon and icemakers you need a seperate generator. You can't do this from an inverter. You don't get owt for nowt.....
 

stevesales

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30 Dec 2004
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Nicaragua
Re: Inverter & Large Battery Bank Questions

You're being too simplistic here, there's an easy solution -
try this
and you get unlimited hot water
 
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