Getting this wiring done slowly!

[simple man]

I started by returning the cart to 36V. I'm using 3 Deka marine deep cycle 12V batteries. I don't know the amp hour rating, but each one is the physical size of 2 Trojan 6Vs ( they weigh a ton ). Next I removed the ground to the chassis. I also disconnected the headlights until I can trace the batt pack negative leads in the harness. These are the only lights on the cart. Here's a few questions : #1- I did a voltmeter test with the + probe on the B+ of the batt pack and the - probe on the chassis. I'm still getting a reading of 27.3 volts! I made a test light using 3 automotive instrument panel bulbs connected in series. When I do the same test there isn't enough current flow to light the test lamp. Should I be concerned about this? Question #2- The headlights are 12V units. Does it matter where in the batt pack the 12V tap is taken from? I do know the mounting is isolated from the bulb circuit ( 2 wires with no connection to the steel mounts ). Thank you guys for all your help! I really appreciate it!!!

[kgsc]

Your first battery in the pack has a wire coming off of it going somewhere that was probably for the lights. Disconnect it until you can chase the wires and your 27.3 should go away.

[JohnnieB]

Originally Posted by simple man

#1- I did a voltmeter test with the + probe on the B+ of the batt pack and the - probe on the chassis. I'm still getting a reading of 27.3 volts! I made a test light using 3 automotive instrument panel bulbs connected in series. When I do the same test there isn't enough current flow to light the test lamp. Should I be concerned about this?

#2- The headlights are 12V units. Does it matter where in the batt pack the 12V tap is taken from? I do know the mounting is isolated from the bulb circuit ( 2 wires with no connection to the steel mounts ). Thank you guys for all your help! I really appreciate it!!!

1. I'm well acquainted with that ghost.
If your DVM has a 10 Mega-Ohm input impedance, you've got about 2.9 Mega-Ohms of resistance between B- and the frame.
When you put a low resistance load (the series of three light bulbs) in parallel with your DVM, it drew more current and more of the available voltage (B+) was dropped across the 2.9 Mega-Ohm Ghost impedance.
Could be a damp wires (Older wires had insulation that absorbed moisture, not enough to pose a significant safety hazard, but enough to be measured, especially if the moisture contained battery acid or backing soda)
Or a conductive path left over from insufficient rinsing after washing off the batteries.
In fact, it might just be slightly conductive dirt.

It also might be the voltage tap as kcsg suggested, but, I think the missing voltage would be closer the the voltage of a fully charged 12V battery if that was the case.


2. No, just as long as you connect the + and - leads to the lights to the same battery. Otherwise you might have very bright lights for a short period of time.

If you have room, it would be best to run your accessories from a stand-alone 12V battery that is entirely separate from the batteries used to drive your cart. Or power them from the 36V battery pack via a 36 to 12 volt converter of some type.

Drawing more power from part of the battery pack imbalances it and cart's performance is reduced by that imbalance. (Just as a chain is only as strong as its weakest link, a battery pack is limited by its weakest battery)

Of course, if you don't run your accessories much, you my not have any problems tapping into the pack to power them.


FWIW: If you really want to scare yourself. Find a metal chassis appliance with a two wire AC plug and measure from chassis to earth ground while it is plugged in. You'll get anywhere from about 25VAC to 95VAC.

[simple man]

Thank you guys! I forgot about " ghost " voltage with a mega-ohm meter! I tried the sweaty arm test again too. I was ready, but no unpleasant surprise I like your idea of an extra battery for accessories. Room is one thing I've got on my cart! It has a 44" by 44" compartment under the deck! I was also thinking of a resistor so I could run the 12V lights from the 36V pack. You'd think someone would make lights in 36 or 48 volts. They'd be much more efficient!

[rabbitreborn]

lmao, the H3 bulb (common for headlights) does come in 36 and 48 volt. As for taillights, I know there are some out there because I have seen them but not sure who is making them.

[simple man]

Originally Posted by rabbitreborn

lmao, the H3 bulb (common for headlights) does come in 36 and 48 volt. As for taillights, I know there are some out there because I have seen them but not sure who is making them.

I found tons of 36 and 48V bulbs of several types online, and at very reasonable cost too! I'm just plain lazy sometimes, and didn't think to use a search engine.

[JohnnieB]

Originally Posted by simple man

........I like your idea of an extra battery for accessories. Room is one thing I've got on my cart! It has a 44" by 44" compartment under the deck!................

I noted in your first post in this thread that you are using "3 Deka marine deep cycle 12V batteries" to get 36V.
Hopefully, you didn't just buy these, but it doesn't matter too much since they probably won't last all that long if the are actually marine batteries.

Joking aside, here's some generic info on batteries for your reading enjoyment.
There are three major types of Wet Cell batteries:
*Starting/automotive. High current for short period of time. Intolerant of deep discharges. Start engine - Immediate recharge.
*Golf Cart/Electric Vehicle. Lower current for a longer time. Tolerant of deep discharges, but the deeper the discharges, the shorter the life span.
*Marine. A compromise of the two.
The difference is in the physical design of the plates.

I'm not certain what Deka means when they say "Marine Deep Cycle" battery. Is it a Marine battery that is designed to be cycled deeper than regular Marine batteries, or is it a true deep cycle battery that can also be used for marine purposes? I'd have to research that more before buying.

In general terms, to get the longest run time, you want the largest number of the lowest voltage batteries you can fit in the space available.
Wet Cell Batteries store electricity as chemical energy in the Lead plates and Sulphuric Acid electrolyte. The larger the plate area and the more electrolyte available to react with them, the greater the amount of stored energy.
A battery is composed of cells and all cells of a Lead-Acid wet cell battery, have the same voltage (about 2V), regardless of physical size. To get a higher voltage, you add cells together in series.
There are exceptions, but wet cell batteries tend to be in about the same sized case, regardless of voltage. Higher voltage batteries having a larger number of smaller cells.

You can make a 36V battery pack out of Three 12V, Four 8V or Six 6V batteries. If the different voltage batteries were in the same sized cases physically, a battery pack made up of 6V batteries would have roughly twice the run time of one made from 12V batteries.

I can't remember if it was you or not, but someone mentioned they had some 12V batteries that were about the size of two Trojan 105 batteries in one case, so three of those would roughly equal 6-6v for run time.

If you could lay your hand on 18 of the monstrous 2V cells the telephone company used to use in their central exchanges, that pack would have a run time two or three times a pack made from 6V batteries.

[simple man]

Originally Posted by JohnnieB

I noted in your first post in this thread that you are using "3 Deka marine deep cycle 12V batteries" to get 36V.
Hopefully, you didn't just buy these, but it doesn't matter too much since they probably won't last all that long if the are actually marine batteries.


I

These batteries were given to me by a friend. I only intend to use them for testing and moving the cart around while I'm working on it. Plans are to get a 48V controller and correct batteries eventually! The motor and solenoid is already 48V. The marine batteries are accessory batteries for a yacht. They say " can be used for starting in an emergency ". Unfortunately only one has a tag on it, and that's all it says.



P.S. Yes it was me who said the batteries are the physical size of 2 Trojans. They are a bear to pick up!