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Forum Index : Electronics : How To Make A Dump Load

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Cameron
Newbie

Joined: 11/04/2008
Location: Australia
Posts: 1
Posted: 07:35am 11 Apr 2008
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Hi,

i am looking for some advice help to make an air resisitive dump load, i am generating 250 watts into a 12v battery bank using a smartdrive hydro turbine that i put together. I want to make a dump load capable of dumping that 250watts when the batteries are full, i have a regulator just need to make something using Nichrome wire or somesort, wire sizes and lengths would be helpful or formulas to calculate what i need.

thanks

Cameron
 
davef
Guru

Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 09:45am 11 Apr 2008
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Well 12Volts at 250 Watts is 21Amps and the resistance to achieve that is 0.57 Ohms.

Suggestion for air: I look for some Nichrome wire, say about 2 meters long that had a resistance of about 0.2Ohms per metre and wrap it around a former. Then get rid of the former and just suspend it on some mounting blocks.

How about water? There are 12Volts water heater elements that suck about that much power. Check out the automotive accessory shops. Use it to pre-heat your cold water rather than dumping it into the air. Assuming you weren't going to dump the heat inside your house.

 
Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669
Posted: 11:25am 11 Apr 2008
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G'day Cameron,
Welcome to the Forum mate.
There's been a number of suggestions on this forum already that a search would bring to light for you.

I like the excess energy go to some useful purpose and as I have plenty of hot water, I choose to use Halogen Downlights. These dissipate 50w @ 12v. So for my micro hydro I use 3 to 4 depending on the jet size I'm running for the available flow. I understand that unlike car headlights of 50w, the 50w downlights do not tolerate over voltages well, so I put in series with each a pair of paralled 1R5 10W resistors to correct for 15v and this now dissipates 65w each giving a total of 260w. Sweet.

50w Downlights can be bought in supermarkets and the little sockets for them from mail order places like Tricky-Dickies or from your local electrical supplier or your local Mitre11(Dump). Now I can't find the 1.5ohm10w resistors in the DSE catalogue so you could parallel 3 x 2R2 5W (cheaper too) but 3 x 2R2 10W for each of the 4 bulbs if money is no object and for greater reliability.

So there's another choice.... Power to Ya.


Edited by Gill 2008-04-12
was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
 
GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127
Posted: 12:22am 12 Apr 2008
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Hi All micro-hydro RE forum members,

surely micro hydro is one of the only RE sources where you have pretty much full control of the energy source. Would it not be better with a battery system to just reduce the water flow to a level that maintains the generator RPM at a level that maintains battery voltage. This would require a split flow and a second jet on the turbine. The main jet would be gated OFF and the power output would decrease to a level to maintain that RPM. There are many stainless steel, or even plastic ball valves that could be activated by the battery sensing cct. Electronic 3/4" ball valve, ON/OFF water tap timers go for about $25 in AUS. The second jet should be added as the main jet efficiency is related to water velocity. A smaller jet would be optimised for the minimum power requirement, to maintain RPM for float voltage.

Maybe Gill could share some expertise here. I have not looked through back posts yet to see if this has been covered by anyone else.

cheers, Gordon.

become more energy aware
 
Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669
Posted: 02:24am 12 Apr 2008
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G'day Gordon,
I'll reply under a new topic 'Hydro Control' as there may be further replies to this 'how to make a dump load' topic.
was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
 
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