Question on Golf Car Batteries.

[Ar]

I know this is off-subject, but I could not find a group that seemed to suit this query. So, if anyone knows the answer, please respond. Or - steer me to a better newsgroup?

My EZGO golf car has the usual six batteries (36V) in series - each

6V.

I need to add 12V headlamps to the front. My tester tells me what positive battery pole and negative pole to connect the hot and ground wires in order to get the 12V. So, I hooked the wires up and even inserted a switch in the hot line so as to be able to turn the lights off & on of course. They seem to work fine.

Then I discovered a neighbor with an EZGO, with factory-installed headlights. On his car, the headlamp grounds are connected to the metal golf car frame.

So, I went back and connected my headlamp grounds to the metal frame instead of the battery negative - now no lights. Yet, my tester tells me a reading of 12v, using the hot lead and ground lead connected to the frame ground.

So, if I get a good 12V reading on my meter why won't the headlamps light? When I then reconnected the headlamp ground to the negative battery pole, the headlamps light again! And of course my tester showed 12V too.

Should I connect the battery negative to the golf car frame? Would that then make the metal frame 12V negative, and light the headlamps? I didn't try it. I was afraid to.

Thanks - yes I am confused.

[Jeff Givens]

I can't imagine that the batt ground isn't tied to the frame. Do a continuity check tween the two. There may be a poor connection somewhere. Check between motor casing and batt neg as well as casing and cart frame.

A voltmeter, a digital one anyways, will show a voltage when there really isn't one. A poor connection can cause a meter to read this but when a load is connected it behaves essentially as open. _________________________________________________________________ JG... Jeff Givens mailto: [e-mail]

"My hovercraft is full of eels."

[Tony Hwang]

Hi, I'd connect as the factory wiring(to the frame ground) and tap (+) from second one from last battery(ground end). It'll give 12V Tony

[dada]

dont forget to fuse the + lead, close to the battery

Joe WB2JQT Newark valley, ny

[Tony Hwang]

Hi, Joe Tony, VE6CGX, Fists #3919

[Ar]

Thanks Tony for your response. And you too Dada. I certainly will fuse the + lead between battery and switch. But, I still worry about the fact that because the batteries are connected in series, there is a battery cable connecting the - pole of the battery (that supplies the 12V ground) to the + (!) pole of the next battery (which my tester shows (to me anyway) to be + and 'hot'. My concern is that that + pole would be 'hot', wouldn't it? What prevents, then, the current from flowing in reverse from that + pole back to the ground and the metal frame ground? Certainly if I connect that + pole to a ground, it should short out shouldn't it?

Can you guys straighten me out here?

[Ar]

Hi again - Tony & Dada -

I called my neighbor that I mentioned before, and he tells me that not long ago his battery immediately next (following) the battery supplying the 12v ground exploded, and had to be replaced.

Now I am scared. Because that would be the battery I previously expressed concern over its + pole possibly shorting to ground. I certainly don't want to explode a battery!

Sorry to be a bother, but I really am concerned.

[m Ransley]

If you dont tap off all the batteries you will never recharge all the batteries, maybe ruining one on discharge and overcharging others. Why not give the lights a separate battery. Then and only then you can monitor charge. Or use a 36v. to 12v. transformer.

[m Ransley]

Neighbors Next battery exploded, ? or failed because of overcharge since it wasnt drawn down from 12v lights.

[Ar]

The battery certainly could have exploded from overcharge. He told me he had just done a charge some 30 minutes beforehand.

Can you explain what you mean by 'If you don't tap off all the batteries you will never recharge all the batteries'? My charger is the one that came with the golf car and charges all the batteries at same time.

Thanks again.

[Tony Hwang]

Hi, You just look at 6 batterries in seires as one big 36 volts one and think you're tapping off at 1/3 point. Don't worry about (+) (-) posts.

Ground--------------------- last (+) post ^ ^ ^

0 volts ^ (ground) 12V 36V

Tony

[Ar]

Okay

Thanks

[Michael Daly]

The problem is that batteries in series should all be charged and discharged at the same rate. By tapping power off of two batteries, you are accellerating the discharge of those two. Hence, they can be discharged lower than the adjacent and become lower in voltage than the others. This will cause the current to flow backwards into the tapped batteries to balance the voltage.

If you're charging the entire series, the four not tapped will be fully charged before the first two (since they are not as fully discharged). The charger will keep pumping power into them to charge the two remaining. Poof!

You'd be best to not tap off the existing batteries at the 12V point. Better to take the 36V and drop it down to 12V - a transformer won't work, since it's DC. You can use a semiconductor- based step down, but if you don't know electronics, it's not an option to make. I don't know how easy it would be to find such a thing off the shelf. DAGS.

I'd recommend a separate 12V battery for the lights. Get a decent deep-discharge battery (AGM is zero maintenance). If you know the current draw and the time of use for the lights between charges, you can figure out the required Ah capacity of the battery.

Mike

[Tony Hwang]

Hi, If that's the case, 6 volts golf cart battery having big cpaacity compared to the current draw of light, we can even install diode isolator then. Smart chargers control charging current any way. Tony

[Michael Daly]

For single batteries, but not for batteries in series. If you're running batteries in series, it's important to keep them matched in capacity and state of charge.

Mike

[Bill Darden]

Please see Section 7.3.5 in the Car and Deep Cycle Battery FAQ on

for information on adding 12-volt accessories to higher voltage battery systems. You need to keep the discharges equal on each battery so they will recharge equally. If it were my cart, I would use a 36-volt to 12-volt DC-to-DC convereter because "half tapping" will only work if you can balance the 12-volt loads across all of your batteries.

Another approach is to use a seperate 12-volt battery and three stage "smart" charger; otherwise, the battery will sulfate from self-discharge. For more information on preventing sulfation (the killer of approximately 85% deep cycle batteries), please see Section

2. Kindest regards,

BiLL......

Kindest regards,

[Dan Lanciani]

You'd think someone would make a 36V headlight assembly for golf carts to avoid the problem of generating 12V from a 36V nominal system. If they don't, how about putting three lamps in series?

Dan Lanciani ddl@danlan.*com