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george357
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join:2009-09-18
Marshall, NC

george357 to cowboyro

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to cowboyro

Re: Need advice on a small water-powered electrical system?

said by cowboyro:

Do some math regarding the flow * drop * efficiency of the water turbine.
A TV will use some 200W assuming it's CRT. Fridge you're looking at 100W almost continuous. You might be able to start a very small one with an inverter, provided that the inverter is capable of 1000W.
So you're looking at a minimum of 100W continuous, maybe 400W for 4hrs/day (throwing numbers). 3.6kWh/day. With a 80% efficiency (let's be realistic) you need 4.5kWh from batteries, maybe 6kWh/day supplied by the turbine. That's 250W continuous. Typical generator efficiency is 60% -> turbine must provide some 400W
Sine you're not going to have a super-efficient turbine (90%+) I would guesstimate 70%.
P=0.7*1000[kg/m^3]*9.8*h*q where h is the drop [m] and q is the flow [m^3/s]
400 = 6860*h*q -> h*q = 0.058
You need 58L/sec falling from 1m to get the power.

Thanks for the info! The TV is either LCD or Plasma will clarify asap, with 100w continuous to the fridge what would u think that the surge would be for start-up of the compressor?

EDIT: Additional information.
We were considering an older automotive generator (not alternator) as the charging source. Would this be feasible or would a purpose designed generator be a better choice.

shdesigns
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Stone Mountain, GA
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shdesigns

Premium Member

Why an old auto generator? My Willys had one. After it fried itself the second time (stuck regulator relay) I swapped it for an alternator and never had problems again.

You can get "1-wire" alternators relatively cheap. I picked up a 200 amp one for just under $100. Included the internal regulator. Just connect to battery and provide +12V to the reg.

If you are just charging a 12V batt, that is all you need.

UHF
All static, all day, Forever
MVM
join:2002-05-24

UHF to george357

MVM

to george357
said by george357:

The TV is either LCD or Plasma

If it's plasma, good luck. Those things are power hogs.

george357
Premium Member
join:2009-09-18
Marshall, NC

george357 to shdesigns

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to shdesigns
said by shdesigns:

Why an old auto generator? My Willys had one. After it fried itself the second time (stuck regulator relay) I swapped it for an alternator and never had problems again.

You can get "1-wire" alternators relatively cheap. I picked up a 200 amp one for just under $100. Included the internal regulator. Just connect to battery and provide +12V to the reg.

If you are just charging a 12V batt, that is all you need.

Just figured that an older generator would be better suited to this application thinking it would require less RPM's to produce the necessary charge when compared to a newer alternator.
said by UHF:

If it's plasma, good luck. Those things are power hogs.

Yeah I know, I have a 50" (though his is smaller 32"-40") and that can pose an issue. I am 75% certain that its an LCD but included the plasma aspect just in case.

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to george357

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to george357
said by george357:

what would u think that the surge would be for start-up of the compressor?

In the 1000W+ range. From what I see in a quick search it can be as high as 20-30A (2400-3600VA) for a fraction of a second. I've been unable to start either of my 2 refrigerators on a 900VA UPS, it would shut down instantly. You made me curious, if I have time tonight I'll try to record on the oscilloscope...

SparkChaser
Premium Member
join:2000-06-06
Downingtown, PA

SparkChaser to shdesigns

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to shdesigns
said by shdesigns:

You can get "1-wire" alternators relatively cheap. I picked up a 200 amp one for just under $100. Included the internal regulator. Just connect to battery and provide +12V to the reg.

If you are just charging a 12V batt, that is all you need.

+1 on the alternator

drjim
MVM
join:2000-06-13
Long Beach, CA

drjim

MVM

And IIRC, when Chrysler was the first to start putting alternators on cars, they made quite a big deal about how it would keep the battery charged even idling at night with the lights on.
Probably moot in this case, as you can change the drive ratio to get whatecer speed you need with the water flow you have.

shdesigns
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join:2000-12-01
Stone Mountain, GA
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ARRIS SB6121

shdesigns to george357

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said by george357:

Just figured that an older generator would be better suited to this application thinking it would require less RPM's to produce the necessary charge when compared to a newer alternator.

More the other way around. My Willys could not charge at idle with the lights on (I had added tail lights.) The alternator had no problem.

Generators are unreliable, brushes wear and they would have mechanical regulators with relays.

I have yet to see a car that cant do a good charge at idle with an alternator.