# sizing a battery charger

R

#### Robert Morein

Jan 1, 1970
0
I'm building a system that will have PV for disasters, and an AC charger to
quickly replenish the batteries after a blackout.

What is the convention for sizing these chargers for use with golf cart
batteries?
A charger spec for a 2 or 3 state charger gives the maximum "bulk" charge
rate.
I can choose
(http://www.donrowe.com/battery_charger/samlex_batterycharger_12v.html)

between a 15, 30, or 45 amp charger.
However, the 15 and 30 can charge a battery while still drawing current from
the inverter, functioning as a UPS.
The 45 cannot, because the charging algorithm can't sense state of charge
under those circumstances.

The batteries will be the standard 220 ah 6v, series-paralleled into one 660
ah 12V bank.

G

#### George Ghio

Jan 1, 1970
0
Robert Morein said:
I'm building a system that will have PV for disasters, and an AC charger to
quickly replenish the batteries after a blackout.

What is the convention for sizing these chargers for use with golf cart
batteries?
A charger spec for a 2 or 3 state charger gives the maximum "bulk" charge
rate.
I can choose
(http://www.donrowe.com/battery_charger/samlex_batterycharger_12v.html)

between a 15, 30, or 45 amp charger.
However, the 15 and 30 can charge a battery while still drawing current from
the inverter, functioning as a UPS.
The 45 cannot, because the charging algorithm can't sense state of charge
under those circumstances.

The batteries will be the standard 220 ah 6v, series-paralleled into one 660
ah 12V bank.

C10 rating.

D

#### daestrom

Jan 1, 1970
0
Robert Morein said:
I'm building a system that will have PV for disasters, and an AC charger to
quickly replenish the batteries after a blackout.

What is the convention for sizing these chargers for use with golf cart
batteries?

If the batteries are only going to be used rarely, consider whether
'golf-cart' batteries are the right choice. These are typically deep-cycle
lead-antimony style intended for a large number of deep cycles. But you
seem to be saying the application is only for rare power outages and the
batteries will be on 'float' most of the time from an AC charger.

This is a different sort of application than many solar PV setups and can
benefit from a different type of lead-acid battery. Large cell 'station
batteries' and other UPS-like batteries with lead-calcium grids can handle
fewer deep cycles, but will provide years of service if kept on a float
charge most of the time (longer than lead-antimony in the same application).

The charging charicteristics are somewhat different between these types and
your charger would have to be for the correct type.

daestrom

R

#### Robert Morein

Jan 1, 1970
0
daestrom said:
If the batteries are only going to be used rarely, consider whether
'golf-cart' batteries are the right choice. These are typically deep-cycle
lead-antimony style intended for a large number of deep cycles. But you
seem to be saying the application is only for rare power outages and the
batteries will be on 'float' most of the time from an AC charger.

This is a different sort of application than many solar PV setups and can
benefit from a different type of lead-acid battery. Large cell 'station
batteries' and other UPS-like batteries with lead-calcium grids can handle
fewer deep cycles, but will provide years of service if kept on a float
charge most of the time (longer than lead-antimony in the same application).

The charging charicteristics are somewhat different between these types and
your charger would have to be for the correct type.

daestrom
I'm designing not just for ordinary power outages, but also for a range of
terror disruptions.
If it was simply a case of a typical power outage, I could simply run the
generator.
However, an extended disruption would use a lot of fuel, and wear out the
generator.
The design envisions a one month power outage, where the battery bank would
be repeatedly cycled, and topped off by the generator.
In this usage, lead-calcium would rapidly fall apart.

If fuel supplies become inadequate, I have purchased two 100W solar panels,
and a 20 amp charge controller.
However, an AC charger would need to be larger to minimize generator
runtime.

I thought that these batteries could be bulk-charged at very high rates, but
comments have suggested C/10 as a goal.

float, ie., zero discharge/charge cycles.
An authoritative answer would be very useful.

W

#### William P.N. Smith

Jan 1, 1970
0
Robert Morein said:
float, ie., zero discharge/charge cycles.
An authoritative answer would be very useful.

And it turned into a real rathole, because you never clarified your
application. Batteries that have zero cyles have an infinite
lifetime, because they always supply all the power required of them.

batteries in terms of Lifetime Energy Units (#define "kilowatt hours a
battery delivers over it's useful life"), and T-105s have 438 of them.
If you use them at 100% DOD or 1%DOD you'll get the same lifetime
(claims Trojan, who ought to know).

N

#### [email protected]

Jan 1, 1970
0
Trojan specifies their batteries in terms of Lifetime Energy Units
(#define "kilowatt hours a battery delivers over it's useful life"),
and T-105s have 438 of them. If you use them at 100% DOD or 1%DOD
you'll get the same lifetime (claims Trojan, who ought to know).

Maybe they've changed their tune. The T-105 DOD vs #cyc curve they faxed
me shows about 750 cycles at 100% DOD (LEU = 473 kWh), 1000 at 70% (441),
1500 at 42% (397), 3000 at 20% (378), and 5500 at 10% (347), so fewer
batteries with larger DODs would optimize the LEU and cost per kWh,

This makes sense to me, since batteries do have a limiting shelf life,
even with no discharging...

Nick

R

#### Robert Morein

Jan 1, 1970
0
Maybe they've changed their tune. The T-105 DOD vs #cyc curve they faxed
me shows about 750 cycles at 100% DOD (LEU = 473 kWh), 1000 at 70% (441),
1500 at 42% (397), 3000 at 20% (378), and 5500 at 10% (347), so fewer
batteries with larger DODs would optimize the LEU and cost per kWh,

This makes sense to me, since batteries do have a limiting shelf life,
even with no discharging...

Nick
Very useful, thanks.

G
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