# Choosing the right battery



## cattlefarmer (Jul 15, 2009)

I’m building an off grid house and need some input on a few products. For the construction I bought an old 2 inverter outback system with AMG batteries for the construction. I plan on keeping the 2 MX60, inverters, AC, and DC boxes but the batteries are toast. It cost me $1,500 and was better than running a genset and keeping it fueled.

So far my new system contains 30 – 200 watt Evergreen panels, a PVSV, hydro turbine that puts out 925 watts, and trimetric. I should receive my 3 XW6048, 2 XW charge controllers, XW system controller, with everything needed to wire it together in about a week.

I have been looking at batteries for some time and I can’t decide on what to get. I want something around 1,800 to 2,000 amp hour (20 hours). I keep looking at getting two 48 volt 1,200 amp hour batteries but for some reason I feel uneasy about getting them; I know what manufacture I want to use if I go that way. There are just too many choices out there and I can’t decide on if I should go with one of the brands that’s more connected to PV.


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## NaeKid (Oct 17, 2008)

I chatted with a friend who runs an industrial battery-shop here in Calgary. What he suggested to me was to run the house on several circuits of 12-volt and then use an inverter only when 110 volt is required or run a generator only when 110v or 220v is required.

The batteries that he suggested are varied.

For areas that would use the most amount of power would be run by 12 batteries at 1-volt each. These batteries are used by telephone companies as their back-up power-systems. When fully charged, these batteries should last several weeks. The circuit for these batteries would go to main living areas like the living-room / dining-room / entertainment-room.

Caterpillar batteries would run another circuit. These batteries are used in the big-diesel Caterpillar tractors / earth-movers and would be perfect for running systems like water-pumps (for the well, for the back-up tanks, for the faucets) - and for your heat-pumps which will help move the air around your house - keeping it cool or warm depending on the time of year.

The next circuit would be run from battery-banks of deep-cycle RV batteries. These would power things like the lights in the house. You might want to run several circuits for lighting - one circuit for all the bedrooms, one circuit for the main common areas, one circuit for emergency lighting only.


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## nj_m715 (Oct 31, 2008)

True deep cells like golf cart batteries can be discharged much further than standard and marine batteries. They are built different, the plates are thicker. I hear good things about trojans. I think alot of guys are using T101's

A desulfer charger will help them last longer. It can even bring some batteries back from the dead. As batteries age crystals build up on the plates and you loos power. A desulator pulses and "shakes" the crystals off of the plates restoring power. You can pick up some used batteries for cheap or free right now and upgrade to trojans as money allows, but it is best to have a matching battery bank all the same age. There are 6 golf cart batteries on craigslist for $250 near me right now. 

You need to watch the water level, but they have special caps that catch most of the water. They need to be topped off much less.


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## cattlefarmer (Jul 15, 2009)

I only want to go with one two strings of batteries in one system. I’m not going to break my system down like NaeKid is talking about.

Golf cart batteries are to small and would require to much work. I have looked at caterpillar batteries but I have heard some bad things about cycling them past 80%. If I could find some new tellcom I would jump all over it. I don’t like AMG and gel batteries. Fork lift batteries have the thicker plates. 

I just don’t know...


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## Fn/Form (Nov 6, 2008)

You seem to have quite a solar setup. Awesome. 

Talk to several battery manufacturers or sales reps. I would call Exide, C&D, Surrette, Deka, etc. They should be able to steer you to their best product for the job or refer you to the person who can. Before you talk to them, make some basic calculations:
1. Your system voltage and projected normal load
2. Desired minimum run-time
3. How many times you will cycle the batteries per day or over their lifespan
4. Battery environment
5. Maintenance level you desire--willing to do monthly maintenance, or do you prefer a low-maintenance battery?

A motive power battery such as "caterpillar" batteries are optimized for temperature extremes, vibration and physical shock, short-term high-rate discharge and eventual replacement. 

A battery designed for stationary use has many more advantages for your setup.

Below is a spiel I wrote on another forum. Apologies if it is old hat.

In a former life I used to work with backup power systems from 300VA to 1.1MVA, including their battery plants. Palm-sized batteries thru dishwasher-sized batteries. Wet cells, gel cell, AGM, "submarine" batteries. Many brands... Yuasa-Exide, Sonnenschein, AlCad, Power, C&D, Johnson Controls, CSB, etc. 

There are many 20yr+ batteries out there. Some of those 20yr models need periodic preventive maintenance (wet cells) while others just need minimal checks (VRLA "submarine" batteries). However, they require climate control for their rated lifespan, as do all the other batteries I've ever worked with.

The industry standard "lifespan" rating for batteries is usually given at around 77 degrees F. Running a sealed/valve regulated lead acid battery at 15 degrees higher shortens SLA/AGM life by 50%. Running a battery at 15 degrees under spec will lengthen battery life but lessen capacity. It's a trade-off. A lot of solar systems I see have batteries stored outside. Eh, not good for long life... especially detrimental if you don't have a temperature compensated charging system.

If you want a 20yr battery, you can find one ($$$$), but you need to consider a lot more than just lifespan. Discharge depth, number of discharge cycles, etc. are important factors. Some batteries are not as well-suited to continual charge/discharge cycles, while others are--at a trade-off of lifespan, capacity, etc. Documents/white papers on their capabilities should be available from the manufacturer.

Keep your VRLA/AGM/SLA/whatever batteries in a temp-controlled or at least reasonably ventilated area (remember, these things live in 65 degree telecom rooms that are mainly concerned with temp control and not ventilation) and perform recommended maintenance. Then you can reasonably expect full life span and performance.


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## Tex (Oct 31, 2008)

With wet cells, you will get longer run time and longer battery life. You also have more problems with maintenance and spill containment. They cost more and are more expensive to replace. Some weigh several hundreds of pounds for a single 2.25V cell. There is usually a longer wait time for your batteries to be made after your order.

VRLA (Valve Regulated Lead Acid) or "sealed cells" are less expensive. The best VRLA batteries will only last about 12-14 years at best. Most last 5-7 years. Since they are cheaper and don't have the capacity of wet cells, they are more often used in series parallel configuration, where you have multiple series strings of batteries tied together in a parallel configuration to increase run time.

Installation and environment will be issues. Batteries work best in a temperature controlled environment. Gassing could be an issue in living quarters. You also need to be careful with exposed battery terminals and unstable battery racks. Especially with higher voltage links and kids around.

Be sure to post pictures of your system. I'd like to see it along with your details about the installation.

If you will be off grid, you will need a diverter load for when your batteries are fully charged and the power is still coming in. I suggest a DC water pump for a diverter load. You can always use more water and store it in a tank for later use. Overflow can water a garden or cattle.

If the old batteries are lead acid, last I saw, you can get about $.10/lb for recycling them. It will help offset new battery costs.

Fn/Form - Who did you work for? That's what I do now in DFW. We probably know some of the same people.


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## tired-medic (Dec 16, 2008)

For a system your size two words come to mind massive & heavy. 2ks33ps or something similar I would think. Just my 2 cents worth.


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## bunkerbob (Sep 29, 2009)

I have a modest size system about 3.7KW. Wind-solar hybrid, a Bergey XL1 supplies the wind side and 22-BP160s and 2-Trina 230s the solar side. The 160s run at 48vdc through an Outback MX60 and the 230s run at 24vdc through the Bergey control panel. Two Trace SW4024s inverters supply the necessary 220vac. I use the T-105 6vdc style batteries for two reasons. First, they are small enough to move and replace by myself without help. Second, they are reasonably priced. I keep them regularly maintained with an equalizing charge and topped off with water. Speaking of water, I contacted the Trojan battery company tech center and asked if it would be ok to use RO(reverse osmosis) water, which I make myself, instead of distilled water, he said no problem. The batteries are going on their 5th year without any problems. I have a 2200 sf home and the bank of 28-T-105s @ 24vdc work just fine. I do have a 12KW propane genset for back-up just in case the system is in need. Also I use a small 30gal elect waterheater plumbed ahead of the tankless waterheater as a dump load when system is maxed out. The Bergey control panel will divert when necessary, their techs calculated the amps and said the stock element would work just fine. 

I was talking to my local battery guy and he said the US Battery recently changed the composition of the contacts and plates, ratio of lead to antimony and stated that they are now more efficient. I use a combination of Trojan and US batteries. The system is a bit sloppy with wiring right now, but is a work in progress with many other projects, See my other posts.


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## Tex (Oct 31, 2008)

Bob - Do you use a tracker? If so, is it worth the expense and hassle?

How do you do your wind generator maintenance? Does the tower tilt or do you have to climb?

Having a fire extinguisher is a good idea. Is your battery room in your house or a seperate building? I've seen batteries go into thermal runaway and it's not pretty.


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## bunkerbob (Sep 29, 2009)

No I do not have a tracker, they are, in my estimation too expensive, I do however use a Outback M60 MPPT charge controller which helps in charge regulation of the solar panels. My wife and I built the rack out of 2" schedule 40 water pipe utilizing the threaded ends to connect, angling the rack at 45 degrees, south facing, concreting in the bottom. 

The Bergey XL-1 wind turbine manual states as maintenance to look up at the blades once a year and look for abnormal wear and listen for bearing noise, that's it. I built a tilt up pole out of schedule 40 steel pipe and added their top bracket to mount the turbine on. I use a gin-pole to raise the unit, and, have not had to lower in three years so far.

The batteries are in my garage, pretty safe, the walls are ICF block sheeted with 5/8 fire rated sheetrock. If you noticed I also use a restaurant style hood extinguishers above the inverters, these are dry and will activate upon flame contact. The plywood backing is also fire rated type. I plan to enclose the batteries at some point.


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