Frostbite [RE-wrenches]

[Travis Creswell, Ozark Solar]

Hi Jeff,

I've been tinkering with the diversion load control feature on a MX60.  We
have a customer with a rarely used off grid hunting cabin.  Don't laugh too
hard when I say this but they have a 240v electric water.  At least I
replaced the 4500 watt element with a 1500 watt.  The customer refused any
suggestions of propane and the system was large enough that it can support
it.

You might consider this set up or some variation of it.  The customer
doesn't want to winterize the bathroom so I installed baseboards which are
hooked up the water heater which is in the super insulated bathroom.  I have
a stat set @ 40f for freeze protection.  It's hooked up to circulating pump
that moves water from the water heater through the baseboards.  

I knew I was throwing a bunch of energy away as the system was in float so
long.  So I've paralleled a 2nd stat set @ 65f that is controlled by a time
delay relay that is hooked up the AUX output of the MX60.  So once the MX60
hits the bulk voltage it turns on the time delay relay which is set @ 4 hrs
to allow the batteries to do a full absorption.  After 4 hrs the time delay
relay closes, if it's colder then 65f in the bathroom the pump turns on and
in a few minutes the water heater kicks on.  The battery voltage gets pulled
down then which turns the AUX relay off which then get the array back up to
full output.  This way I'm using a lot more of the energy even if it is just
to keep an unused bathroom warmer.  The trick was the time delay relay.

So far it's working.  I left a temp data logger (similar to a HOBO) up there
so we'll see just what's going on when I get a chance to look at the data.
I'm sure I'll still need to do some playing with the timing and voltage
settings but the concept is sound.


Best,

Travis Creswell
Ozark Energy Services



-----Original Message-----
From: Todd Cory, Mt. Shasta Energy Services
[mailto:toddcory at finestplanet.com] 
Sent: Wednesday, February 15, 2006 8:32 PM
To: RE-wrenches at topica.com
Subject: Re: Frostbite [RE-wrenches]

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I did an off grid system for a client near anchorage. Same thing, they 
are gone for the winter and didn't want the batteries to freeze. As long 
as they are kept fully charged it should not be a problem. In fact I 
think you greatly elevate the risk through possibly lowering the SOC by 
heating the pack.

 From Trojan's web page.

Can a battery freeze?
The only way that a battery can freeze is if it is left in a state of 
partial or complete discharged. As the state of charge in a battery 
decreases, the electrolyte becomes more like water and the freezing 
temperature increases. The freezing temperature of the electrolyte in a 
fully charged battery is -92.0^o F. At a 40% state of charge, 
electrolyte will freeze if the temperature reaches approximately 16.0^o F.

Todd

Jeff Oldham wrote:

>Your free subscription is supported by today's sponsor:
>
>Anyone have some cleaver and RELIABLE tricks for keeping batteries from
freezing up in AK where I can see -40F for long winter periods? In the past
I've placed them in 9' deep root cellars with great luck (stays at 32F) but
this client is not interested in that approach. 
>At this point I'm considering electric soil warming mats under the
batteries in a well insulated box. I can probably spare 2 or so kWh/day. No
one will be there for at least 3 months.
>Thanks!
>-jeff o
>