5000W/ 48V water heater dump load element [RE-wrenches]

[David Katz]

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I have been dumping excess DC into my hot water storage tank for 15 
years. It works great.  I charge with 3KW of PV and a seasonal 
hydroelectric system an I have 3 times as much power as I need in the 
summer, so I use it to make hot water.  I use and MX 60 to drive a small 
relay that drives a 60 amp mercury contactor. I use to use an Enermaxer 
to PWM the water heater.  The Morningstar Tristar does a great job of 
this, too. We have sold more than 1000 DC water heaters for 12, 24 and 
48 volts, so plenty of people are doing it.  It is very popular with 
wind and hydro systems where you have to dump excess power.
You can also use the inverter to dump AC, which might be easier. You can 
use smaller wire and control  the AC with a relay driven by the MX60.
Be careful with the MX60 relay output. It can only drive a 200mA coil. 
It cannot power a mercury contactor or large relay with coil current 
higher than 200 mA. Use a 12 volt coil relay, even if your system 
voltage is 24 or 48 volts. The output of the aux in the MX60 is always 
12 volts.  It is also a good idea to have a backup control so if 
something fails you don't overcharge the batteries.
David

David Katz
AEE Solar, Inc.
formerly Alternative Energy Engineering
1155 Redway Drive - Box 339
Redway, CA  95560  USA
Phone 707-825-1200
Fax 707-825-1202
email david at aeesolar.com
www.aeesolar.com

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Dan Brown wrote:
> happy holidays everyone.
>        i have an off grid customer hell bent on eeking every last watt out of 
> a 10k bergy (in a fairly hot wind site). they heat with water-- so they're 
> thinking of using a conventional hot water tank with elements capable of 
> handling up to 10k (5k each) as a dump load, i see basically the same idea, but 
> instead of using a domestic hot water heater, I'd rather instal the element in 
> their existing boiler either way, we'd tap in to the DC side at 48 volt, and 
> control the mess with an outback aux out. question is has any one tried this 
> approach (and lived to tell the tale) -- good idea? bad idea? parts? suppliers? that 
> kind of thing. seems their using both radiant floor heat, and base board. we 
> have talked a little about a hot water storage system (like a tarn), but i get 
> the impression they'd like to keep things less expensive. any advice would be 
> greatly appreciated. thanks dan
>
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