battery charger for battery backup sump pump

[moldmaker]

what kind of battery charger should i use for
my battery backup sump pump for my home?
they are two 12 volt sealed lead acid marine batterys.<p>thanks

[dyarker]

By including "backup", I guess that means most of the time an AC powered pump does the pumping. So a simple trickle charger should do.<p>You didn't say if batteries are series or parallel, or anphour rating. Assuming parallel, a 15VDC wall wart and a resistor.<p>Cheers,

[moldmaker]

the batterys are parallel,
they are rated at 105 ah<p>i just dont want to over charge them<p>what size resistor would you recomend<p>[ October 16, 2004: Message edited by: moldmaker ]</p>

[dyarker]

Cheezz, 210AH! That must pump must keep the basement dry during a hurricane with no power for days!!!!!!!!!!<p>I found a data sheet for a Panasonic LC-X1265P, so extrapolate from there.<p>Self-discharge is 9% over 3 months.
210AH * 0.09 = 18.9AH down every 90 days.
18.9AH / 90 days = 0.21AH down per day.
0.21AH / 24 hours = 0.00875A continuous self-discharge.<p>The trickle charge must greater than that to keep the batteries topped-off. More as they age. The less, the better. Let's say 0.025A, and a 15V supply.<p>15V - 13.7V = 1.3V
1.3V / 0.025A = 52 Ohms. 51 Ohms is a standard value.
1.3V / 51 Ohms = 0.0255A
1.3V * 0.0255 = 0.033W.<p>So a 51 Ohm, 1/8W or 1/4W resistor.<p>That's just standby maintenance charge. After the batteries are used you'll need a 10A to 15A charger (or wait 6 months).<p>Cheers,

[dyarker]

Assuming the pump draws zero current when not running.<p>Otherwise recalculate the current for trickle plus whatever the water sensor/controller uses.

[fsdenis]

I ran across commercially available "BatteryMINDer" chargers that seem similar to what you guys are discussing. You might find their ad interesting.<p>The ad is in Northern Tool and Equipment catalog number 1502 on page 112.<p>Northern has a web address: NorthernTool.com<p>These chargers have a desulphation feature called PulseMode desulphation circuitry. I don't understand what sulphation is, what it does, nor how it does it, but you guys might.

[moldmaker]

desulphation is when you take off
the plating off the cells on the battery from
the battery acid<p>check out this web site
it goes into more detail
www.shaka.com/~kalepa/desulf.htm<p>what about a battery charger with a float

[fsdenis]

Thanks moldmaker. Good site.

[bridgen]

Sulphation is the build-up of lead-sulphate crystals on the positive plate, not the lead coming off it. <p>The lead-sulphate crystals increase the internal resistance of the affected cell. <p>The traditional cure is a long slow charge, which often needs to be repeated. <p>It would seem that the pulsing method works too.