Golf cart batteries

hillside · August 2016

Hi, I have somewhat limited choices of batteries where I live and recently replaced my small system with 4 Interstate Power Fast golf cart batts. #GC2, 208AH, Reserve capacity 107 @ 75A. This is a small system, 515 watt with 3000W pure sine inverter, 24 volt, used for washer/dryer (propane dryer) and general backup when the electricity goes out. These batteries do not state "deep cycle" on them. Are they? Maybe it's the fact that this has been a very cloudy summer but it seems I'm not getting the usual power output. (tried the search box but no "go" button, so apologies if this has been beaten to death before) What do you think of golf cart batteries?

BB. · August 2016

No problems asking questions. I personally use Google search with the "site:" tag that limits search to a specific website:

site:http://solar-electric.com golf cart battery (the http// part of the URL is not needed)

Generally "golf cat" batteries are deep cycel type (Marine batteries are not really true deep cycle batteries).

So--We start with the basics. First you should have 5% to 13% rate of charge for your battery bank from a 515 Watt array:

515 Watt array * 0.77 panel+controller deratings * 1/29 volts charging * 1/0.05 rate of charge = 273 AH @ 24 volt maximum battery bank
515 Watt array * 0.77 panel+controller deratings * 1/29 volts charging * 1/0.10 rate of charge = 137 AH @ 24 volt nominal battery bank
515 Watt array * 0.77 panel+controller deratings * 1/29 volts charging * 1/0.13 rate of charge = 105 AH @ 24 volt minimum battery bank

Or looking at it from your battery bank point of view:

208 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 392 Watt array minimum
208 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 783 Watt array nominal
208 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,018 Watt array "cost effective" maximum

So--if your system is intended for weekend / seasonal (summer) use--515 Watt array is OK... If you are trying to use the system daily 9+ months a year--your array is a bit on the small side. Especially if you want to use power during the day (at the same time your array is charging your battery bank).

Also--For a 208 AH @ 24 volt battery bank--You can really only expect (plan) on around 1,000 Watt (1 kW) maximum continuous power output (hour+ at a time).

A 3k Watt AC inverter, on that size battery bank, is a bit on the large size.

A common problem is "deficit charging" of the battery bank. Start at 100%, discharge to 80%, recharge to 95% discharge to 75%, repeat... Basically, not enough charging vs actual power usage.

Need to look at/understand your loads. What is your present energy usage--Do you have a Kill-a-Watt type meter to measure your AC loads?

And have you looked at your electrolyte specific gravity levels using a Hydrometer?

How much charging voltage are you seeing on your battery bank? Are you seeing ~29.0 volts for ~2-4+ hours per day (average sun day)?

And how much charging current are you seeing on a typical day? An average peak (cool/clear spring/fall day at noon with properly configured array+controller):

515 Watts * 0.77 panel+controller derating * 1/29 volts = 13.7 Amps (peak realistic charging current noontime into low battery bank)

-Bill

softdown · August 2016

I recommend golf cart batteries quite often. They are highly affordable and don't usually create bankruptcy proceedings when the owner discovers one of the one hundred ways to kill a battery.

You have grid power...which is cheaper than the wear and tear on batteries. Though I could see where solar experience and equipment would pay off if the grid goes down for a very long time due to a solar flare or EMP.

hillside · August 2016

Bill, thanks for your detailed response. Much of it is over my head though, which is why I almost posted in the Beginner's corner. I'm in the Caribbean and we don't have cool days...the sun bakes the crap out of the panels, basically. And there are no local experts to help out with things, so I'll stumble along here as best I can. Have not checked charging voltage lately and it's overcast yet again so tomorrow, if possible. Don't have a Kill a Watt but will look into it. I used a hydrometer to check them when installed (2 months ago) but not lately...tomorrow! If I were to add another panel to the array would a 235 watt be enough, or too much? Thanks much, (to you too, softdown.)

vtmaps · August 2016

hillside said:

If I were to add another panel to the array would a 235 watt be enough, or too much?

What controller are you using? What is the configuration of your existing 515 watts of solar panel? (hint: you can put that in your signature)

--vtMaps

softdown · August 2016

It is often a good idea to get new panels that match, more or less, the "architecture" of your old panels. In other words...similar panels if possible.

This board is very helpful. Yet it ties their hands behind their backs when they do not have information on panels and charge controllers.

jonr · August 2016

Continuing softdown's point, your best bet might be to not run the washer/dryer off the system. Ie, I suggest more details about your goals and the economics before you start "fixing" the system.

hillside · August 2016

more info tomorrow, thanks. Appreciate the help!

hillside · August 2016

OK guys, we made it until about noon before the clouds came. Early morning, sun just covering panels= 26.3 V Noon, 28V, and just before the clouds we had 30.7V at the charge controller. Which is a Steca Solarix PRS 3030, 12/24V, 30Amp. The panels are 4 older Shell 70 watt each, and one Trina 235 watt. The inverter is a Cotek 3000. The batteries' charge I'm wondering about, as of 10:00 AM, specific gravity showed 1.225 all around. Now, at 1:15PM they are showing 1.250, both readings in the "Fair" range. We often run a .4 (point 4) amp fan at mid-day to use up what we thought was excess power, for 1-3 hours, so maybe I'm not letting the batteries get to full charge. We only use it when the charge controller shows green #2 flashing and the inverter shows flashing red led which indicates over input voltage. The washer is used once or twice a week (only 2 of us) and it's a 9Amp. horizontal motor type. Dryer is used even less and it's propane heated & 6Amp. I'll not use anything until I see a rise in specific gravity on the batts. Does the inverter use much power overnight? Jonr, the goal is backup power (we also have a Honda 3000w EU Gen.) to use the washer/dryer and if possible I'd like to run the TV at night. In the winter months we seem to get much more output from this system as the sun is in a better position and there's a lot less cloud cover. Thanks again for the help.

westbranch · August 2016

there are only a few factors you can adjust,
1. the voltage can be raised or lowered (more PV will add both V and Amps and would shorten the time in BULK)
2. the voltage setting for ABSORB up or down, and
3. the amount of time you maintain the ABSORB, then finally
4 the FLOAT voltage up or down

So, now please tell us what the current settings are....

from your last post it sounds like your Absorb phase is about a few (3?) hours long...

littleharbor2 · August 2016

How are your panels configured? You have four older 12 volt panels and one 20 volt nominal grid tie panel. Are these all paralleled ? Your controller is a PWM type which is designed to accept battery bank nominal voltage. It doesn't step down higher voltage. The one grid tie panel isn't compatible and at best will act as a much smaller panel. Mixing different voltage panels isn't something you should be doing.

jonr · August 2016

> Does the inverter use much power overnight?

Over a week, probably several times what the washer/dryer use. Can you turn it off when not in active use?

Drawing from the batteries during non-sunshine hours may cost more in battery wear than what utility power costs. If that's true, do you still want to run the TV from the batteries?

You might want to put a charger on a timer to make sure that the batteries get a full charge, independent of solar performance.

hillside · August 2016

After a fairly good day of mostly sunshine the batteries show only 1.250 specific gravity. I've shut down the inverter and will see what tomorrow brings, letting them charge all day with the inverter off (it is now also). Another thing is I recently moved the battery bank outdoors from the basement to a narrow alley way with concrete and block wall on one side and basement wall on the other, This area is shaded but much warmer than inside the basement. So, temps. are in the 85-95 degrees in this area. would the higher temps matter? The panels were set up by a local solar professional who mainly does full house and commercial installs. I believe he is knowledgeable enough to have set the panels up right. He's hard to find these days, business is down a lot for him mainly because the local gov. has stopped their overspending...(it's Puerto Rico!) Kinda sounds like this'll be an expensive re-do..

westbranch · August 2016

not necessarily... it may just need a little tweaking and a bit more PV... well matched that is. Just depends on what you want out of the system.

hillside · August 2016

Another question...If I put a couple of ounces of distilled water in them 4 days back would it affect the specific gravity reading? What I need out of the system is as much as possible. If we get a hurricane, past history shows we will be without grid power for 3 months.

softdown · August 2016

Yes...SG could easily be affected. The fluid you are checking is at the top of the battery where the distilled water is added.

Three months without grid power? I would be thinking about more panels. Panels that work together.

Putting your batteries in a warm location will shorten their life a great deal. The cooler the better for battery longevity. Out Canadian friends often enjoy tremendous battery life in their frozen igloos (a joke).

vtmaps · August 2016

hillside said:

Another thing is I recently moved the battery bank outdoors from the basement to a narrow alley way with concrete and block wall on one side and basement wall on the other, This area is shaded but much warmer than inside the basement. So, temps. are in the 85-95 degrees in this area. would the higher temps matter?

Temperature matters. Your controller should have a remote battery temp sensor.

When batteries are warmer than standard conditions they require lower charging voltages. If your controller does not lower the charging voltage, you may be overcharging your batteries which makes them warmer which makes them draw more current which makes them warmer which makes them draw more current which makes them warmer which makes them draw more current... It's called thermal runaway. Dangerous.

By the way, every 10° C increase in temperature cuts the batteries lifespan in half.

--vtMaps

hillside · August 2016

What do people in Arizona do to keep battery temps down? We're no hotter than most southern states this time of year..:) Have not checked SG yet today...soon. Thanks, guys.

hillside · August 2016

The good news is today only had 3 hrs. of sun but the batteries have all come up to 1.275, so I'm encouraged about the batteries not being damaged. I should look at taking the 4 older 70W panels out and replacing with 2 of the same Trina 235W units? For a total of 3?

Johann · August 2016

hillside said:

OK guys, we made it until about noon before the clouds came. Early morning, sun just covering panels= 26.3 V Noon, 28V, and just before the clouds we had 30.7V at the charge controller. Which is a Steca Solarix PRS 3030, 12/24V, 30Amp. The panels are 4 older Shell 70 watt each, and one Trina 235 watt. The inverter is a Cotek 3000. The batteries' charge I'm wondering about, as of 10:00 AM, specific gravity showed 1.225 all around. Now, at 1:15PM they are showing 1.250, both readings in the "Fair" range. We often run a .4 (point 4) amp fan at mid-day to use up what we thought was excess power, for 1-3 hours, so maybe I'm not letting the batteries get to full charge. We only use it when the charge controller shows green #2 flashing and the inverter shows flashing red led which indicates over input voltage. The washer is used once or twice a week (only 2 of us) and it's a 9Amp. horizontal motor type. Dryer is used even less and it's propane heated & 6Amp. I'll not use anything until I see a rise in specific gravity on the batts. Does the inverter use much power overnight? Jonr, the goal is backup power (we also have a Honda 3000w EU Gen.) to use the washer/dryer and if possible I'd like to run the TV at night. In the winter months we seem to get much more output from this system as the sun is in a better position and there's a lot less cloud cover. Thanks again for the help.

The 9 amps and the 6 amps ...at what voltage will they use the 9 and 6 amps and for how long are those running at a time?
Are you washing and drying while the sun is out?
How many watts per hour does the TV use and how many hours per day are you using the TV?
Any other loads hooked up to it?

hillside · August 2016

The washer/dryer are 120v, 60Hz, washer runs about 35 min. Always when the sun is out and second green light is showing at chg. controller. Previous Inverter showed voltage display, current one does not. Not sure how many watts per hr. the tv uses. Specs show "Max current" 2.65A, "Power Consumption" shows 0.6W in standby mode. No other loads are hooked up. By this afternoon the batteries should show a full charge; the inverter has been off for 36hrs. Lots of cloud cover these days. Planning on 2 new matching panels and out with the 4 70W's.

softdown · August 2016

I would think that digging a hole a few feet into the ground would work. Could make maintenance a nightmare. Just an idea really.

It never gets over 59 F in my root cellar. Cold air sinks. Hot air rises.

hillside said:

What do people in Arizona do to keep battery temps down? We're no hotter than most southern states this time of year..:) Have not checked SG yet today...soon. Thanks, guys.

hillside · August 2016

That would be tough, it'd have to be a concrete poured box, too much rain here. They're in a box of sorts now, partly dug into the hillside. It's just hot here in summer, and very humid. What to you think of me switching to the newer matching panels?

Johann · August 2016

hillside said:

The washer/dryer are 120v, 60Hz, washer runs about 35 min. Always when the sun is out and second green light is showing at chg. controller. Previous Inverter showed voltage display, current one does not. Not sure how many watts per hr. the tv uses. Specs show "Max current" 2.65A, "Power Consumption" shows 0.6W in standby mode. No other loads are hooked up. By this afternoon the batteries should show a full charge; the inverter has been off for 36hrs. Lots of cloud cover these days. Planning on 2 new matching panels and out with the 4 70W's.

Volts times amps = watts
120 volts X 2.25amps = 270 watts per hour.

softdown · August 2016

You raised an important question. Start a thread. I'm sure our grizzled veterans have some ideas. The solar pro$ may have expensive ideas.

hillside said:

That would be tough, it'd have to be a concrete poured box, too much rain here. They're in a box of sorts now, partly dug into the hillside. It's just hot here in summer, and very humid. What to you think of me switching to the newer matching panels?

jonr · August 2016

You will be much better off getting a kill-a-watt and actually measuring usage.

BB. · August 2016

Technically, 270 Watts (no per hour) = Rate

270 Watts x 35 minutes / 60 minutes per hour = 157.5 Watt*Hours per cycle.

-Bill

Golf cart batteries

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