(ET) Fw: Re: (no subject)

[David C Robie <mycroftxx1 juno com>]

--------- Forwarded message ----------
From: David C Robie <mycroftxx1 juno com>
To: noaddress drmm net
Cc: elec-trak cosmos phy tufts edu
Date: Thu, 13 Jul 2006 19:36:49 -0400
Subject: Re: (ET) (no subject)
Message-ID: <20060713 235429 -384943 3 mycroftxx1 juno com>

I figure 'normal' to be what GE puts out.  And this never overcharges any
judging by water use.  The mowing here is on the average of every 10 days
in season and that seems to fit what the sun puts out.  As for winter
there's less sun, and less tractor use.  Experience shows these a good
match.   Incidentally; When I see full batteries in both tractors in the
off seasons,  the panels get connected to a heater in the basement
workshop to help a tiny bit with street gas consumption.  Used to do
water heat with it but the shop heater cycles more than the water tank
here.
Dave
Weymouth MA

On Thu, 13 Jul 2006 13:01:02 -0400 "David Roden" <etpost drmm net>
writes:
> On 12 Jul 2006 at 21:42, David C Robie wrote:
> 
> > These are self regulating under the premise of the old '5% rule, 
> in that
> > anything under 5%  of a batteries normal fast charge rate will not 
> damage it.
> 
> Well now, I'm not so sure I can agree with that rule.
> 
> For lead-acid batteries, I guess it depends in part on how you 
> define 
> "damage."  A battery on constant charge *will* overcharge, and it 
> *will* 
> fail eventually from positive grid corrosion.  How long that takes 
> depends 
> on the charging rate and ambient temperature, but even a battery on 
> true 
> float degrades.  That's why you have to replace the battery in your 
> computer 
> UPS now and then, even if it's never cycled.
> 
> If the charge rate is low enough, and the application not too 
> demanding, it 
> may take 5 years or more for the battery's capacity to decline 
> enough to 
> matter.  Or, the battery may fail or fall below usable capacity from 
> other 
> stresses first.  But I don't agree that there's some arbitrary 
> amount of 
> overcharging that doesn't damage a lead battery.  Any overcharging 
> does.
> 
> My other concern here is : what is a "normal fast charge rate"?  A 
> lead 
> battery can be charged to 80% SOC as fast as it can be discharged - 
> meaning 
> hundreds or (for some batteries) thousands of amps - as long as 
> temperature 
> is monitored.
> 
> A charge rate in the range of C/50 (that is, the amp hour capacity 
> expressed 
> in amps, divided by 50) can be used for a long time - on the order 
> of 
> several days - without serious harm.  This is useful for equalizing.
> 
> But for charging that never stops, the rule of thumb I'm familiar 
> with for 
> lead batteries is that if the battery is to be under charge all the 
> time, it 
> should be held at float voltage on a regulated, 
> temperature-compensating 
> charger.  The float voltage will vary a bit by battery manufacturer, 
> but a 
> typical recommendation is 2.2 to 2.3 volts per cell at 20 deg C.
> 
> 
> David Roden - Akron, Ohio, USA
> 
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