Re: [Paddlewise] electric pumps

On 24 Sep 2003 at 12:48, Warner Family wrote:

> If I go the electric route I was thinking of installing a 500 GPH Rule
> pump powered by a 1.9 gel battery.

Look at the Attwood 625 (or is it 650?) - more pumping capacity with 
better power demand (only 0.9A vs 1.9A).

> Can someone make an informed
> guess at how long it would take to pump out a small cockpit
> (114cmX48cm) after a capsize re-entry and roll?

Brian gave you an estimate, but I'd add that when I do roll and 
rescue practice, I rarely see the cockpit more than about 1/3 full in 
relatively calm water.  A wave breaking over the empty cockpit could 
change this, of course.

> The battery will power the pump for one
> continuous hour of pumping.  Is that enough power?

You should only need a few minutes at a time.  Assuming the regular 
Rule 500 (not the automatic) model 29-25D, it draws 1.9A.  With a 
1.9Ah gel cell, that's one hour to a full drain.  Note that the 
Attwood I mentioned abouve draws only 0.9A in my kayak and would last 
two hours under the same conditions.

However...

> Do gel batteries have a memory?  Should they be drained to absolute
> zero before recharging? 

No memory, but never drain to zero.  The gel cells should be deep 
cycle types, but even that can mean different things between types.  
The manufacturer should be able to give you the exact discharge 
characteristics.  Yuasa, for example, has the spec sheets for their 
batteries online in PDF form.

In general, if a deep cycle lead acid battery is discharged less than 
20%, it should have maximum life.  Some of the better batteries can 
be discharged to 50% repeatedly.  Only a few can handle 80% discharge 
on a regular basis without seriously restricting their life.  Best to 
assume that 50% is the worst case and design accordingly.  IOW, if 
you think you need 1Ah capacity, get a gel cell battery that's 2Ah.

For your 1.9Ah, assume a worst case of 0.95Ah available on a regular 
basis.  This means the Rule will run for 1/2 hour and the Attwood for 
an hour.  You will be stressing the battery somewhat, since it's max 
discharge rate should be a fraction of its capacity.  The Attwood at 
c/2 is still high, but should be ok for occasional use.  C/1 with the 
Rule is high.

> And finally does anyone familiar with electric
> pumps have any battery recommendations they'd like to make?  I was
> taken aback at the weight of some of these gel batteries.

Consider a pack made up of 12 AA NiMH batteries in series (14.4V 
total).  These can be discharged to 90% repeatedly with no loss of 
performance for at least 500 cycles.  An average AA NiMH today is 
around 1.8Ah, so it would be even more powerful than the 1.9Ah gel 
cell after conservative use is considered.  NiMH can handle C/1 
discharge rates.

The important thing about a AA pack is to make sure all 12 batteries 
are at the same state of charge.  Never mix fully charged with 
partially charged in the same pack.  In use, the partially charged 
will over-discharge and toast the whole pack.

I can get 12AA name brand for about C$45.  That's comparable to the 
price of a gel cell.  In the US, they're somewhat cheaper.  Get a 
good charger, preferably a "smart" charger that monitors each battery 
individually.

BTW - the Honda Hybrid uses NiMH batteries.  I believe that the 
Toyota does as well.  

Mike

PS - here's a good web site on batteries.
http://www.buchmann.ca/faq.asp

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