DC-DC Conversion questions [RE-wrenches]

Drake Chamberlin solar at ecoisp.com
Fri Dec 24 10:03:11 PST 2004


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At 01:01 PM 12/23/2004 -0700, you wrote:
>How successful have you been running existing motor and compressor loads
>through DC-DC stepdown converters? I am specificially asking about DC Sun
>Frost fridges, and 12 and 24-volt Shurflo 2088 and 9300, and Flowlight
>Booster pumps.

Several times I've center tapped the battery bank and balanced the charge 
on the respective halves of the banks.  The Vanner unit works very 
well.  There are less expensive sources of battery bank balancers that do 
the job well.

One code issue that is a little maddening is that 2/0 and larger cables are 
permitted in battery compartments.  It may be necessary to bring power out 
of the battery enclosure with a 2/0 cable when a number 6 would be adequate.

A good strategy might be to run a third cable through the conduit from the 
battery box to the DC disconnect enclosure.  A 2/0 could be run with the 
4/0 cables in a SW4024 system.  If you used THHN, you would be allowed to 
run three 4/0 cables in a 2" Sch 80 PVC conduit, the THHN (IMHO) is not the 
best choice for battery enclosures since it is somewhat soluble in battery 
acid.  The RHH RHW  type cables would require a 2 1/2" Sch 80 PVC.

When you also add the expense of bonding the center points of the various 
series sets together, it can make a DC to DC converter a cheaper and easier 
option.  In my opinion, the converter is not as good as pulling directly 
off the bank, especially for larger loads.  A DC Sunfrost does fine on a 
converter.

Another issue is finding equipment approved by a recognized testing lab, 
such as UL.  What converters and balancers are approved?

Drake 

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