[RE-wrenches] bad battery = system overvoltage = dead inverter

[James Jefferson Jarvis]

Hi Dan,

You can do it!

You are looking for a circuit called a crowbar. It is a SCR that turns 
on when a certain voltage is exceeded. Typically implemented with an SCR 
and a zener diode. The SCR, when turned on, shorts out the battery. And 
BAM you blow the big fuse in the battery bank or before the load you are 
trying to protect. So the SCR needs to be able to handle the fuse 
blowing current for just long enough to blow the fuse.

http://en.wikipedia.org/wiki/Crowbar_%28circuit%29

You could make a variant of this that trips a shunt trip circuit 
breaker. Midnite sells some shunt trip breakers that could be suitable. 
More expensive to do it this way, however.

-James Jarvis
APRS World, LLC

On 3/15/2013 10:05 PM, Dan Fink wrote:
> This has been happening all too frequently here. We live in a big area
> of off grid homes, dozens of systems.
> Lost a customers Trace 2624 this morning; One L-16 in older 24v bank
> opened internally. PV array/MPPT control zorched inverter as soon as
> the sun came up. First indication of problems last nite when customer
> hit microwave to warm up dinner and inverter went crazy. This morning
> the bad battery showed 3.2v (yes, I would expect 2 or 4 also) the rest
> the usual 6+v. Turned on PV array, bad battery immediately up to 11v
> (yes, 6v L16).
>
> Somebody needs to build a "battery condom" with big stacked diodes on
> a big heat sink or some such solution. A voltage brick wall for system
> charging inputs. MPPT PV controllers do NOT protect a inverter from
> input overvoltage if all or part of the battery bank disappears! And
> last year we saw a nice battery box fire and zorched inverters due to
> similar -- dual 48v L16 strings, one cell failed and opened, other
> string dumped everything into the bad one, smoke and flames. Parallel
> fusing would have stopped that......but not stopped the loss of dual
> stacked XW inverters from PV overvoltage.
>
> Or am I missing something here?
>
> Dan Fink,
> Executive Director;
> Otherpower
> Buckville Energy Consulting
> Buckville Publications LLC
> NABCEP / IREC accredited Continuing Education Providers
> 970.672.4342
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-- 
-James Jefferson Jarvis
APRS World, LLC
+1-507-454-2727
www.aprsworld.com