[RE-wrenches] 72V Battery question

[Sindelar Solar]

Kris,

I see that apparently to date no Wrench has responded to your question, 
so I'll give it a wild-ass go. Although I've never used or even seen a 
72V controller, I'll suspect from your description that it was made by 
Dan Pringle of Solar Converters, now long gone.

But based on the limited information you have provided, I don't 
understand your question. A DC pump is not normally regulated by 
voltage, but by either a pressure switch, if it's a single-pump 
pressurized system, or by a float switch in a dual-pump system with a 
storage cistern. Cut-in and cut-out voltages would be set only to 
protect the batteries from overvoltage and excessive discharge, and 
these settings would be independent of what was being operated, in this 
case the pump. Given this, if the DC relay (with a 12V coil to work with 
the Midnite aux port) is there to set these battery protective limits, I 
would suggest that you determine the conventional LBCO and HBCO voltages 
for a 12V battery and multiply by 6 for 72V. Most likely at 72V, the 
current would be quite low unless it's a huge pump, and DC pumps in 
general have little surge, so a fairly low LBCO would be more acceptable 
than with a lower voltage system, all other issues equal (which, of 
course, they never are...).

Allan

On 7/2/2020 7:02 PM, Kristopher Schmid wrote:
> Greetings All,
> I have inherited a stand alone system at a state park originally 
> installed by Currin Corporation out of Michigan (I think that he did 
> work in a number of state parks in the region).  Good install, but the 
> custom designed 72 volt controller (a Canadian company that slips my 
> mind at the moment) crapped out.  I replaced it with a 72 volt midnite 
> controller and all is well except...
> The original system used a dc relay to disconnect the 72 volt dc 
> submersible well pump.  I kept the relay in the circuit controlled by 
> the midnite aux port. Since I was unable to read any programming from 
> the old controller, I am not sure where to set the cut-in and cut-out 
> voltages for the pump relay.
> Battery bank: 12 Deka MK 8G27 (72 volts, 176 ah)
> Pump current: unknown at the moment
> Anyone?
> Thanks,
> Kris
>
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-- 

*Allan Sindelar*
allan at sindelarsolar.com <mailto:allan at sindelarsolar.com>
NABCEP Certified PV Installation Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
*505 780-2738 cell*

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