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CCWKen
10-08-2003, 12:18 AM
This is a little off topic but I will be doing some milling for this later.
I picked up a 36v DC golf cart. This cart uses 6, yes SIX!, 6volt batteries. I'm wondering if I can use 3-12volt batteries instead.
The original battery locations are three on each side, for balance I suppose. The battery trays are all but eaten away and I was going to rebuild them. Why couldn't I just use three 12volt batteries?
I could get more reserve capacity and even deep cycle batteries for less than six 6volt batteries. There's room to mount one on each side and one in the middle. (If I move the resistor pack).
I'll also be converting it from 3-wheel to 4-wheel. That's where the milling will come in. I'll need to build the front axle assembly.

jfsmith
10-08-2003, 01:08 AM
I think the reason those carts used the 6 volt batteries was the power level they have, this is why many tractors still use them. Check the amp load to start the electric motor (peak output) for the 6 6 volt batteries vs using 3 12 volt batteries.

Jerry

Jim Hubbell
10-08-2003, 01:45 AM
I am quite sure the three 12v batts will put out enough to run the unit. The amp-hr is where you have to be careful. A very rough way to evaluate is by weight. Two 6v batts should weigh about the same as one 12v batt. It takes a certain amount of lead to hold the power. If the 12v batts are not "heavy enough" you will run out of "gas" more quickly.

Evan
10-08-2003, 02:31 AM
Sure, it'll work. As a four wheeler put two on the right and one on the left. Is the driver still going to sit in the middle?

darryl
10-08-2003, 02:43 AM
It's all in the amp-hour rating, and the discharge characteristics. Deep discharge batteries are called for, in any case. Three 12 volt batteries will be fine. Just don't expect car batteries to live very long in that application. Six volt batteries are generally pretty rugged.

Evan
10-08-2003, 02:59 AM
You can also use two sets of 12 volt batteries, 3x12in series, parallel with 3x12 in series. They should be connected together with a couple of big diodes at one end so they don't try to charge the set that goes dead first. Same with charging, through a couple of reverse connected diodes so the sets charge seperately. One of IBEW's diode bridges should work. As I recall my golf carts, you should have room for six 12 volt deep cycle batts to get the total required amp hours for full range.

rmatel
10-08-2003, 08:12 AM
Thr 6 volt "golf cart" batteries are designed for high output, deep discharge. Marine deep discharge batteries, usually 12 volts, are not designed for high output; therefore their lifespan in a golf cart will be less than the 6 volt ones. I'm not sure what the ratio is but you might end up paying more over time by using the less expensive 12 volt batteries. Whichever you choose, recharge the batteries as soon as possible after use; lead acid batteries don't do well discharged.
Bob

CCWKen
10-08-2003, 09:39 PM
Thanks guys. The best 6volt battery I've found is 460cca with a reserve of 190a. A very good median 12v battery was 1000cca with a reserve of 400a. I'll have to admit, I don't understand all I know about reserve. The math here says 3x12 is better and cheaper.
The cart will be used for trips to the mail box and trash-can hauling. It will get two trips a day. One to get the paper and one to get the mail. Each trip is about 1/2 mile (round-trip). If I make a low power charger (2-10 amp), do you think this would keep the batteries up? Seems like a golf outing would put more strain on it.
The occasional tour with the grand-kids might need special charging though. Also, lights will be a must in winter. Those early morning paper runs in the dark are dangerous out here. (Wild dogs, cats, rabbits, deer and snakes)

darryl
10-08-2003, 10:10 PM
Sounds like your 12's are the way to go. What will eat them quicker is repeated high current demands, ie jackrabbit starts. I'm not sure this is even possible in a golf cart, but ? I would also think running it on grass would eat more power than on pavement, or hard pack gravel or dirt. As far as charging the pack, you'll need to supply about 44 volts to get them to take a full charge, and 40 volts trickle to keep the charge peaked. Consider about a 15 - 20 amp charge rate, and an intelligent charger so you don't damage the pack. It wont make much difference if you charge 6 six volters, or 3 12 volters, from whatever charger is made for the cart. I'm guessing here, but I think you'll be drawing about 20 to 30 amps average just for cruising at an even speed, on smooth level ground. Much larger peaks to accelerate, of course. However much time you put on it, that plus about 20% more will have to be put back into the pack. Some experimenting will give you an idea of how much current will be needed, given the time available to put the charge in, and the length of time you're willing to run the charger. It would be good to know how much trickle current is recommended for the batteries you do use.

Oso
10-08-2003, 11:35 PM
rmatel has it right on the money.

It may not matter for you, though.

If you were going to run the cart hard, you would kill the 12V batteries.

Deep discharge 6V will each weigh more than a 12V car-type battery.

There is more electrolyte (acid) and more lead in a deep discharge battery. They won't be killed by an 80% discharge.

A car battery isn't made for that, and it will be killed as the sulphate (discharge product) flakes off the plates.

BUT, you won't probably do much damage with a short trip and a re-charge.

BUT, the CCA is BS for battery quality. It merely shows low battery resistance, and does not indicte capacity.

The ONLY spec that shows capacity is ampere hours. That is the total capacity at a specified discharge rate, normally at the 10 or 20 hour rate, i.e. the current that will totally discharge it in 10 or 20 hours.

Short deal, car batteries are for short bursts of very high current, but should not be drawn down far in total charge. They last about 4 or 5 years in car service, or maybe 20 to 40 deep discharges

Deep cycle are best for long deep discharges at lower currents. They should not be used for starting duty, because very high current isn't good for them. They can last 10 years or 1000 to 2000 deep discharges.

Doubt it will bother you much, and the car batteries will be cheaper, even if you have to replace them faster.

dplugs39
10-09-2003, 12:26 AM
To CCWKen.....Just a thought, why not use six 12volt batteries ?? You will have to wire two 12 v. batteries in pairs + to + and - to -, do this with all three sets of 12 v batteries, and then connect them ( the three pairs) in series to get your 36 volts you need to run the cart....You can use (cheap) less cost than deep discharge batteries, and still keep your current capacity needed to drive the cart...If you are going to rebuild the battery tray , you can build the tray to fit the new batteries......Dale Detrich

Evan
10-09-2003, 12:50 AM
Dale

I already pointed that out. If doing so they must be connected with isolator diodes to avoid problems. Also, the batteries absolutely MUST be of the deep discharge type or they will only last four or five discharges before the plates crumble completely. That applies no matter what configuration is used.

Oso,

I use deep discharge batteries for my Land Rover because of the high current demand of the electric/hydraulic system that raises my snowplow blade. This is a unit with a starter motor driving the pump, cycling every few seconds while plowing. The battery also starts the Rover in -20 weather. One will last years in this duty. There is no way the alternator can keep up with it over an hour or so that it takes to plow my driveway with the pump, the electric rear window heater, the headlights, rotating flasher, four tractor lights and other electrics. I let it charge after use by running for ten or so minutes. Works great.

[This message has been edited by Evan (edited 10-09-2003).]

Evan
10-09-2003, 12:18 PM
BTW, the "Reserve Capacity" rating may be used to calculate the amp hour capacity of the battery. It is how long the battery can supply 25 amps in minutes before the terminal voltage drops to 10.2 volts (for a 12V batt). So, if the battery is rated at 120 Reserve Capacity then it is a 50 amp hour battery.

A Reserve Capacity of 400 means it can supply 25 amps for 400 minutes or 166 amps for one hour, theoretically. This is not necessarily the case as sucking 166 amps continuously will probably boil the electrolyte. Also, this rating is at 80 degress F. If used at 32*F the capacity will be much less, perhaps 1/2. It is still useful for comparing battery capacity.

With any battery the amp hour capacity does not mean you can drain it at that rate in one hour. It is simply a measure of the total power the battery can deliver.

Weston Bye
10-09-2003, 01:13 PM
If using isolator diodes you must take into account the 0.7 Volt drop across the diode junction. Each diode must be capable of carrying the full current that the motor can draw. Current flowing across a voltage drop (resistance) will create heat. The diodes must be suitably heat sinked or life will be short.

Wes

Oso
10-09-2003, 01:43 PM
The problem with other ratings is usually "unrealistic" currents, or lack of sufficient info.

CCA is OK for starting, but gives no info about capacity or long slow discharges.

The "reserve capacity" is OK, but 25A may be unrealistic if the battery is sized to the typical load.

A typical 6V deep cycle is 220 A-H, like a Trojan "Mileage-Master" T-105.
For that, 25A is OK, close to the "10 hour rate".

For a smaller capacity battery, it is very conservative, the actual capacity is larger the lower the discharge rate due to internal resistance and losses. The "10 hour rate" is a generally accepted discharge rate, giving a standard comparison.

For a larger battery, it may be a tiny discharge, giving too large a capacity rating.

Batteries hold energy, and energy is wasted by resistances in proportion to current squared.

Most deep cycle are Ok with reasonable discharges, at least up to the 1 hour rate, or 220A in the example. I draw 200 A from a series-parallel 4x6V (12V) system regularly, and they have lasted 8 years so far. Gravity and charge maintenance is still good. They will probably go 15 years.

The problem is that often the plates and pasting isn't optimium for large current, so relative inequities in charge state and acid strength occur across the plate during a heavy current. Then parts of the cell have to do extra work, others loaf.

A starting battery has probably lower capacity per unit volume, but has good electrolyte circulation and electrolyte penetration of the plates. That gives max performance at silly discharge rates like 600A from a little battery. That is almost like a short across the terminals. The most cranking capacity is when the load impedance is the same as the battery impedance, pretty darn low......Different from what deep cycle batteries are about.

To get both, you make a battery like that on a forklift. Huge.

And you do NOT have to isolate parallel batteries....they will settle their own relative charge states.

It is best to cross-connect each set of cells, that equalizes the charging voltages. Example...I have 2 in parallel with a piece of 4/0 between them, then 2 more in parallel, again with 4/0 between, in a 12 V system using 6V units.

Others have more paralleled, in 12 or 24V PV systems and there isn't a problem. Systems in use for 10 years with no failures.

The "weaker" batteries will simply float at the same voltage as the stronger.

If one of a parallel set goes really bad, it may draw down the others, but that is easily found.

Any individual cell can be considered as one, or as several smaller ones in parallel. Inside one enclosure, they typically see about the same acid strength, but even that isn't guaranteed, due to circulation.

Typically the 1 to 1.5V loss (at good current) due to a diode is as serious an energy loss as the small capacity loss of parallel batteries if one is a little weaker.

Evan
10-09-2003, 02:05 PM
Oso,

I presume the batteries you are dealing with are for static use, that is, not in an application subject to shock and vibration as in a vehicle. Those are a different kettle of fish from a vehicle or marine deep discharge battery. The marine deep cycle batteries have a different plate structure (than ordinary auto battery) to retain the lead sulphide paste under vibration as well as antimony free plates to reduce electrolyte gassing during long discharge cycles. They also have more space under the plates to allow more debris buildup before shorting occurs.

With a battery in vehicle use I would use isolator diodes, just at the end of a series of batteries since there is much more likelyhood of one battery going bad due to use conditions (vibration) which would not be good for the rest of the connected batteries.

If you have two sets of three 12V as I suggested in earlier post and use two diodes to isolate each series set from the other, you lose perhaps 1 volt, about 3% of 36 volts. That's not much. It will allow the system (golf cart) to work even if one set of three is dead.

Thrud
10-09-2003, 03:10 PM
Replace the batteries with Optima 6 volt batteries - you should never have to replace them again.

The 6 V Optimas have the same current output of a 12V Optima. Dual 6V is the trick set up for winching.

Oso
10-09-2003, 05:13 PM
Evan....

Your description of Marine deep cycle sounds pretty much like most deep cycle batteries....

Actually, the ones in question are golf cart batteries.

Car batteries have a construction aimed at cheapness, reasonable vibration ruggedness, and very high current capability. No other considerations are really important to them, certainly not lifetime.

Standard pep boys "marine deep cycle" are not the same as the real thing.....They are really just trolling motor batteries.

But for the mailbox run, I doubt that anything will be too bad to use.....if recharged.

Try some Auto batteries, must be some cheapies where you can get hold of 3 for not that much $$.

[This message has been edited by Oso (edited 10-09-2003).]

CCWKen
10-09-2003, 08:13 PM
Interesting thread.
Thrud, the whole idea was to keep from spending $600 for batteries. That would buy a lot of starters and ignition switches. I could just keep using the truck for that!

I only paid $50 for the cart!

docsteve66
10-13-2003, 05:42 PM
Ken: I advise going with the golf cart 6 volt batteries. I agree with all OSO says EXCEPTING paralleling batteries. Even there you can probably get away with no problems.

The reason I say do not parallel is that a small current (amperage) flows unless the batteries are well matched (plate size and internal impedance. Two new batteries will have very little "cross current", as they age of if a new battery is installed the problem is more likely. But if you go to golf cart batteries you only need a single set anyway, so the problem is moot.

A few years ago, in motor home (RV) (but i have a TOAD car to jumper with), I converted from two 12 volt batteries, to two 6 volt golf cart batteries. The RV manufacturers used a switch to select the 12 volt batteries and to parallel them. THe capacity was kind of low and I had to switch to the "reserve battery" or crank generator when dry camping any length of time in cold weather.

I went to "sam's" and compared prices- the golf cart batteries, when capacity is considered are cheaper, than deep cycle/marine batteries. Of course with this set up, I am using my engine starting battery when I use the "house" load. If I ever run out of juice on the house i am also out on the engine, which means i can not start the generator either. Thus, the toad vehicle is nice to have (with jumpers). One of those "jumper batteries" will start the generator (barely).

One really deep discharge may reduce the capacity of the "deep cycle" battery by 50 percent. It is not realistic to compare automotive use to golf cart use. Evan says his alternator can not keep up with his loads- his is a unusual application. Car batteries should be used only to start the engine and MAYBE at idle. Rest of the time they are mainly along for the ride and waiting to be used to start the engine.

When buying automobile batteries i use cost per month (and warranty- which is unbelievably complicated in some case) to decide which to lay my money down for. I figure I am really renting or leasing the battery. If it lasts longer than the warranty, I have bought it. Most fail me so near the warranty end that i get little use of warranty- local sales determine where i buy in most cases.

Don't look so much at the initial expense, as at the long term expense. I think you will decide golf cart batteries are the better "investment"
Steve

Oso
10-13-2003, 11:46 PM
Steve is correct, if cost is no object.

I would agree totally with him, but you said you wanted cheap "first cost", meaning what it costs you to get going.

That means using what you can get that will "work".

3 12V "whatever" batteries might cost you $100 to $150, depending on your local choices.

The golf cart ones may cost you $70 per each, and you need 6.


Your choice.

[This message has been edited by Oso (edited 10-13-2003).]

darryl
10-14-2003, 12:38 AM
Wow. All of our discussions of batteries so far have led to the conclusion that it's going to cost you, one way or another. Proper ones for the job = more money up front. Cheaper ones = less money now, but repeat that expense again too soon. If you knew that the end was coming, and the lifetime of the expensive set wouldn't get used, it would be more logical to get the cheaper set. When the availability of money, or buying power, is limited, the choice is easier, you have to go cheaper, or don't get the product. Otherwise, it's a mental excercise to determine individually what is an acceptable decision to come to, and implement. And live with. Good luck to you, Ken, with the electric cart experience, and to all who engage in electric vehicle experiments. I'd love to see it become more practical than fuel in the long run.

CCWKen
10-15-2003, 12:54 AM
Thanks for all the input on this guys. I'm leaning toward the views of cost-benifit and price-value. I think I'll just bite the bullet and go with cart batteries. I've got some body rebuilding in mind (custom) and I think I be using it for some time. At least until something better comes along.

Checking the price of carts, I could probably get my money back. That $400+ sure could buy a lot of tooling though.