Deep cycle battery charger and power backup

sprdave · March 2013

Im looking to put together a small battery backup system. Something for lighting (up to 350w of T5 fluorescent), possibly a fridge, for a few hours. So far Im thinking two 6v deep cycle "golf cart" batteries, like the Crown CR-235 or US Battery 2200. An pure-sine inverter like Xantrex Prowatt SW600.

Not sure about charger, want something with quick recharge to maximize any generator run, but inexpensive. The cheapest Ive found is the PowerMax PM3-35 (35A) for about $100. Is this the cheapest one suitable? Is 35A too much for 235AH batteries considering it will be rarely used?

Any other suggestions on the system? Is the SW600 suitable for the lighting or a fridge? Any good places to buy batteries online or is shipping always a killer? Or any good local stores near (north) Detroit?

Photowhit · March 2013

Re: Deep cycle battery charger and power backup

I don't know how to recover my writing, but got bumped at midnight don't want to go through all that work again. So....

You need to define your loads, "a few hours", "a fridge" doesn't cut it.

A 600 watt inverter might not start your fridge, with a 350 watt load.

Do you need 350 watts of light?

Sams club and Costco have reasonable golf cart batteries at around $75 + core or $15.

35 amp charge is likely fine, it's a 3 stage charger so should sense and back off as completeing the charge.

350 watt is 29 amps at 12 volts x 1.15 for inverter inefficentcies = 34 amps this is a very high discharge rate for 220 amp hour battery and likely not good for more than 2 and a half hours before your dipping below 50% capacity.

Cariboocoot · March 2013

Re: Deep cycle battery charger and power backup

Not likely a 600 Watt inverter is going to start a refrigerator. See if you can find a Prosine 1800 or 2000 with built-in charger. That plus the higher capacity = all problems solved.

But you really should get a better handle on your intended loads. That's what the Kill-A-Watt meter is for. Best energy investment anyone can make.

Photowhit: if you have to restart a post after getting dropped there should be a button in the lower left that says "restore from autosaved" (something like that) which will bring up as much of your original post in that thread as was automatically saved as a draft before the disconnect. (Ever notice the little yellow flag that pops up every now and then while you're typing that says "Auto Saved" then vanishes?)

sprdave · March 2013

Re: Deep cycle battery charger and power backup

It's to either run lighting in washrooms/showers at a campground in power outages, or bring to the house to run lights or fridge. There is only one generator between the two locations. If there was a way to power some lights, it would save having a second generator and minimize run time. Keep in mind this is just for power outages - it might only be used a couple times a year.

It's "up to" 350w of lights (measured by a kill-a-watt and lamp specs), more typically 200w (and Im thinking of having a way to switch some fixtures off to keep it to 200w). A few hours meaning 2-4 hours, depending on how long 2 batteries would last. The fridge draws 165w running (the killawatt did "catch" about 1000w on startup) and wouldnt be trying to run other things at the same time, but most likely would just run it off the generator anyway.

Would a Schumacher SC-8010A (or another Schumacher) charger be suitable? It does 10-25A and seems automatic, and is $50 or so.

A Prosine would be really nice, but $1000+ isn't in the budget for all the use it will see.

Cariboocoot · March 2013

Re: Deep cycle battery charger and power backup

Only used a couple times a year means batteries sitting around dying slowly even if kept charged. Kind of a waste of money right there.

One of the problems with a Schumacher charger is that they are designed for automotive applications, not deep cycle. As such they don't go through the 3 stage charging routine that keeps deep cycles happy. Fine for Bulk charging on an as-needed basis, but I wouldn't expect batteries to last if that was all there was to keep them charged with.

Better than that would be something like these: http://www.solar-electric.com/12vobach.html
Yes, I know; more money than you hoped to spend. But it's really not possible to do the job right and cheap.

For occasional power you may be better off with a second generator instead. Inverter + batteries + charger can add up fast.

BB. · March 2013

Re: Deep cycle battery charger and power backup

A Honda eu2000i (1,600 watt) or eu1000i (900 watt) would be a great way to go (or the Yamaha/other inverter-generator types).

They are very fuel efficient with low loads (i.e., the eu2000i will run >9 hours on 1 gallon of gas at 400 watts or less). And pretty easy to pull start (no electric start for the smaller units).

You can store 10-20 gallons of gasoline (with fuel preservative) for up to a year, and rotate it back into a vehicle. Or, there are some after-market propane conversions that might make more sense if you have lots of propane nearby.

Gensets don't use any fuel or age (very much) when not used. Just empty them of fuel between uses (the Hondas have a carburettor drain screw--and I run them dry after emptying the tank) and keep good oil in them.

Otherwise, you could go the route of a battery bank+AC Charger+Inverter with Transfer Switch--And just size the batteries for a couple days of no-sun (and even plan on using a genset for longer outages to recharge).

When you look at the energy storage of a battery bank--It is pretty pitiful. For example. 4x 6 volt * 220 AH batteries--a pretty useful size of battery bank. And, assume that you draw them down 50% over 24 hours (i.e., 12 hours of light at night for two nights).

4*6 volt * 220 AH * 0.50 max discharge * 0.85 inverter eff * 1/24 hours = 93.5 watt average load

Now lets look at a Honda eu2000i running 400 watts for 24 hours and 1 gallon of fuel per 9 hours of run time (run 12 hours per night for two "nights":

400 watts * 24 hours = 9,600 Watt*Hours of energy
4*6 volt * 220 AH * 0.50 max discharge * 0.85 = 2,244 WH of energy (without battery damage)
24 hours / 9 hours per 1 gallon of fuel = 2.7 gallons of gasoline (over two nights)

Way more energy available from that $10 worth of gasoline. And a lot more portable too (if you need power at different locations, for construction away from the utility power, etc.).

If you can keep your loads small (LED lighting vs running a fridge), the battery system may be perfect--And you can setup automatic fail over (aka, automatic transfer switch with small inverter, or get a "nice" inverter or inverter/charger with internal transfer switch--basically a UPS with external battery bank)... Depends on what you need.

LED Lighting--battery with AC inverter+transfer switch. Automatic, nobody would even know the power went out.

Running a fridge/freezer, and more substantial power--A genset would be hard to beat for occasional power failures (and use propane if you don't want the hassles of gasoline storage).

-Bill

mtdoc · March 2013

Re: Deep cycle battery charger and power backup

One of THESE Meanwell charges will do 3 stage charging (up to 24 amps at 14.7V) , are power factor corrected (for better fuel efficiency with genset) and are only $85. :cool:

This charger and an eu1000i would be perfect for your proposed battery bank.

Inverter wise - a Xantrex Prowatt would be the best bang for the buck in a TSW inverter IMO. You could probably get by with the Prowatt 1000 which can be had for about $250.

But -depending on the true start up surge amp requirement of your fridge you might be pushing it with this inverter. Then again if you need more amps than a 1000 watt inverter can handle, you will probably also need a larger (more AH) bettery bank to supply those amps. And don't forget to have fat cables from battery to inverter if you want to deliver those surge amps fast enough.

Deep cycle battery charger and power backup

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