Which Battery Charger?

Snowblind · December 2020

Currently I have been running a 200 ah agm battery to power a cpap machine during power outages. I charge the battery with a 10 amp marine charger from the grid and keep it on standby when all is well. I would like to add two more 200 ah batteries for a total of three in series. I have no idea what type of charger to get for this setup. Anybody have any suggestions? Any help will greatly be appreciated. TIA

mike95490 · December 2020

Snowblind said:

Currently I have been running a 200 ah agm battery to power a cpap machine during power outages. I charge the battery with a 10 amp marine charger from the grid and keep it on standby when all is well. I would like to add two more 200 ah batteries for a total of three in series. I have no idea what type of charger to get for this setup. Anybody have any suggestions? Any help will greatly be appreciated. TIA

3 batteries in series yields 36V @ 200ah   Chargers are rare

Sure you are not thinking of PARALLEL ? That would give 12V @ 600ah.
But parallel AGM batteries is a tough nut to make work well.   It's likely OK with just a CPAP machine as a load.
Is this an every day thing, or only for PSPS safety outages that can last 3-4 days ?
If daily, you want a charger that can be set to the Daily Cycle Use.   If just a couple times a year, use the Float Cycle Use voltage setting. So you need a charger that covers your style of usage.

Connections / wiring .   See method 2 at   http://www.smartgauge.co.uk/batt_con.html
this is critical to getting longest life out of your AGM batteries, which likely have a 5 or 6 year lifetime,

BB. · December 2020

If you want a "fast" charger--Look for a ~10% rate of charge, a (600 AH battery bank * 0.10 rate of charge = ) 60 Amp charger, about 5 hours to mostly charge a 50% discharged bank, and another 2-6 hours of "absorb" charging to finish the last 10% of charge).

Xantrex makes a very good set of chargers called the "TC2" family (and great for use on a small genset):

https://www.solar-electric.com/residential/batteries-battery-storage/battery-chargers.html?manufacturer=101&nav_charger_output_voltage=491

Iota makes a range of chargers that will output rated current for hours/days on end reliably--Not very expensive. Look for the IQ4 "smart charging" module (either as an option, or built in)... IQ4 is the "brains" for charging/floating (vs just floating) a battery bank.

Or, if you want do not need a fast charger, you probably could get away with a 1% to 2% rate of charge (600 AH * 0.02 = ) 6-12 amp "float" charger.

I have this one for float charging a car which does not get used much. Has settings for AGM/Sealed batteries (lower charging voltage to prevent damage to AGMs from "higher voltage" charging:

https://www.amazon.com/BatteryMinder-128CEC1-Charger-Maintainer-Desulfator-Motorcycles-Snowmobiles/dp/B01D3SWXUA

Not cheap--But has worked for many years (used to replace the battery every few years because a) the battery went dead from modern electronics and slow drain over a few months, or b) because the "cheap" float chargers would eventually "boil" the battery dry.

When you get into higher charging current AC chargers--The larger ones can exceed the output wattage of smaller (like the Honda eu1000/2000/2200i family gensets (900-1800 Watts or so)...

The TC2 and some other chargers have "power factored" corrected AC inputs which are "more efficient" at using AC current for charging (i.e., a non-PFC supply may max out a Honda eu2000i at ~25 to 30 amps of 12 volt charging current... A TC2 can output 40 amps and not over tax the eu2x00i genset).

Anyway... Some ideas and suggestions.

-Bill

Which Battery Charger?

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