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# Backup Battery for Gas Fired Boiler

## Backup Battery for Gas Fired Boiler

#1
10-16-14, 06:44 PM
Member
Join Date: Oct 2014
Location: United States
Posts: 3
Backup Battery for Gas Fired Boiler

I have an indirect fired boiler and I want to setup a battery backup.

I was thinking that I could start with a 110v battery charger to 12v battery to inverter 12v to 110v to automatic transfer switch to fuse to boiler switch.

My question is if I have a 12v 110 Ah battery and the boiler draws about 5-6 amps, how long will this battery power the boiler?

Whats the math for computing this?

#2
10-16-14, 06:49 PM
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Join Date: Oct 2012
Location: Jersey
Posts: 63,919
Welcome to the forums.

If efficiency was 100% then it would be 110 / 6 = 18 approx max/hours.
Realistically more like 12-15 hours.

#3
10-23-14, 12:48 AM
Member
Join Date: Oct 2014
Location: United States
Posts: 3
now i am confused.. i have this other reply from another site...

6a x 120v = 720w.
720w / 12v = 60a.
Average size car battery = 120ah.
120 / 60 =2.
Theoretical maximum.
Reality probably 1 hour.

Help.. Who's on First???

#4
10-23-14, 01:30 AM
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 63,919
Hey.... I'm on first but incorrect. I didn't convert to 12v.

#5
10-31-14, 02:00 PM
Member
Join Date: Oct 2014
Location: United States
Posts: 3
ok.. expanding.. i found that my boiler draws 3-3.2 Ah ... i also found a 6v 208 Ah Energizer Golf battery for \$85.. if i tie two of these together.. will i have a 12v 416 Ah battery system... if so.. will the Ah keep increasing for additonal batteries... if not.. what???

#6
10-31-14, 02:14 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 9,785
Whatever you do make sure the batteries are either stored outside, or are very well ventilated. Hydrogen gas will vent from the batteries and create an explosion hazard if they are indoors. For indoor use, something like a computer UPS which utilizes sealed lead acid batteries would be more appropriate.

#7
10-31-14, 02:15 PM
Member
Join Date: Sep 2009
Location: USA
Posts: 477
If you tie two together in series you'll have 12 volts 208 ah.
If you tied them in parallel you'll have 6 volts and 416 ah.

It would take 4 batteries to get your 12 volts and 416 ah.

#8
03-14-15, 02:52 PM
Member
Join Date: Mar 2015
Posts: 1

I have an indirect fired boiler and I want to setup a battery backup. I was thinking that I could start with a 110v battery charger to 12v battery to inverter 12v to 110v to automatic transfer switch to fuse to boiler switch. My question is if I have a 12v 110 Ah battery and the boiler draws about 5-6 amps, how long will this battery power the boiler? Whats the math for computing this?

I did this last year. 100 amp hour, DEEP CYCLE, SEALED, marine battery, no hydrogen gas issue with SEALED battery (no caps, no maintenance whatsoever). 1000 watt PURE sinewave inverter, automatic transfer switch (I think used with RVs on campsites to switch from gen to grid), and a 7 stage smart charger.

It lasts about 18 hours on an average winter day about 30 degrees. Two such batteries (200 amps total if connected in parallel) would last a day and a half.

I also hooked in a 4 switch reliance control bypass, and so we have heat, AND LIGHTS, during a power outage, after we shut the generator off for the night.

BOOYA.