DIY Electric Car Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
In a 42v Western Golf Cart there are 7 - 6v batteries. Can 3 - 12v batteries be substituted for 6 of the 6v batteries?
 

·
Registered
Joined
·
4,765 Posts
In a 42v Western Golf Cart there are 7 - 6v batteries. Can 3 - 12v batteries be substituted for 6 of the 6v batteries?
A 12-volt battery can certainly be substituted for two 6-volt batteries. Of course not all batteries of the same voltage are created equal, so they would need to be three appropriate 12-volt batteries.

The big challenge in this case is that if you want to maintain the same nominal system voltage (42 V), you would be keeping one 6-volt battery; for that to work well the characteristics of the 12-volt battery (amp-hour capacity, etc) would need to match the remaining 6-volt battery. It seems unlikely that you would be able to find that.

Why would you want to change just six of seven batteries? :confused:

The common nominal system voltage for golf cars and similar low-speed vehicles is 48 V, and it appears that 36 V is - or was - also common (not 42 V). For 48 V, typically either six 8-volt batteries (the standard configuration) or eight 6-volt batteries (the upgrade configuration for more power or range) are used, although I've seen photos of 4 x 12V installations. Can you change this vehicle to a 48-volt setup? If you already have some 12-volt batteries available, would performance be acceptable on 36 volts?
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
Thanks Brian; The Western Cart was manufactured with 7 - 6 volt batteries with a 42v controller. I was just thinking the less batteries the less weight and less cost to replace the next time but if the specs won't match up that may not be possible. What are the requirements to match the 3 - 12v batt with 1 - 6v? if the ampere hour are the same is that all that is needed?
 

·
Registered
Joined
·
966 Posts
Are those really wired in series?

My old c-car had something called an “aux” battery that ran lights, contactors and dash stuff.

It was separate from the traction batteries
 

·
Registered
Joined
·
4,765 Posts
I was just thinking the less batteries the less weight and less cost to replace the next time but if the specs won't match up that may not be possible. What are the requirements to match the 3 - 12v batt with 1 - 6v? if the ampere hour are the same is that all that is needed?
Simply changing from 6-volt to 12-volt batteries won't save you any weight at all. For a given total capacity, whether the lead plates and electrolyte are divided into two boxes (two 6V batteries) or in one battery (one 12V battery) doesn't make any difference to total weight.

Lead-acid batteries are sets of 2-volt cells. The number of cells that you combine into one box - which determines the total voltage of that battery - makes no difference to the behaviour of the cells. 6-volt batteries are just sets of three cells; a 12-volt battery of the same size is just a set of cells which are each half as large.

For the batteries in a series set to match, the most basic requirement is that they hold the same amount of energy per cell, so during discharge all of the cells are evenly discharged. For one cell, stored energy is just the product of the cell voltage (nominally 2 V for all lead-acid) and the cell capacity (e.g. in amp-hours). That means that the cells must be about the same size. A 12-volt battery (6 cells) is twice as large (twice the volume, twice the weight) as a 6-volt battery (3 cells) with the same size of cells.

The least expensive golf car batteries, for a given amount of energy storage, seems to be in 6-volt batteries of the "GC2" size, simply because that's a very common size. Certainly a 12-volt battery with twice the energy (twice the weight, same amp-hour capacity and twice the voltage) would be more expensive than two 6V GC2 batteries.
 

·
Registered
Joined
·
4,765 Posts
Are those really wired in series?

My old c-car had something called an “aux” battery that ran lights, contactors and dash stuff.

It was separate from the traction batteries
So, six 6V batteries in series to drive the motor, and one separate battery for the other stuff. Interesting. :) A voltage converter would be obvious and more convenient, but that wouldn't have been so practical a couple of decades ago.

The auxiliary battery configuration would make a lot of sense to explain the seven batteries, but then the nominal system voltage for the drive system would be 36 volts. It's possible that the 42 volt rating of the controller is not the nominal voltage, but instead is the maximum voltage (since a set 18 lead-acid cells, such as a six-by-6V series set, put out about 42 volts when fully charged).

In that case, there is no need for the traction batteries (the six 6V set or their replacements) to match the single auxiliary battery, since they're not used in series with each other. The six 6V batteries could be replaced by three 12V batteries, but for the same capacity each of the 12V batteries would be twice as big as one of the 6V batteries, so the total weight of batteries would be just as high. The big 12V batteries would also likely be more expensive.

I think it's time to trace the battery cables and determine how those batteries are actually wired.
 

·
Registered
Joined
·
738 Posts
The original OP idea is a complete non-starter.

All the batts in a bank should be the same model, ideally all the same production run, matching voltage, ideally matched internal resistance.

Mixing different voltages would result in an early death for all members.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #8
Thanks guys, I kind of thought that it was a no starter but was thinking I could save on weight. Yes the 7 batteries are wired in series and 12v lights and horn are wired from two of the batteries. I will ask the manufacturer of the controller and motor if they can handle 48v which will allow me to use 4 - 12v or 5 - 8v. Thanks again for all who replied.

Dan
 

·
Registered
Joined
·
966 Posts
5x or 6x 8 volt batteries would work well in your existing boxes and provide much better range and reliability than 12 volt batteries.

40 volts will work fine in a 42 volt lead system but your charger would need adjustment.

In 99% of 42 volt systems 48 volts will work fine, again your charging system would have to be swapped, soc gage also won’t work.

Also using 2 of your traction batteries for aux is a sure fire way to wear out batteries quicker,
I would at a minimum use a separate non- traction battery for aux or a dcdc converter to “fix” it.


I would like to know the model and brand charger in that rig

42 volts is a very rare antique configuration, almost as rare as 14 volt lead belt batteries used by broadcasters.

Good Luck
 

·
Registered
Joined
·
5 Posts
Discussion Starter #10
Thanks for the reply; The charger is a Lester, Model 14390, type 42LC25-8ET
DC amps 25. The Western Golf Cart company took 36 volt EZgo carts and put a different body and added one more 6v battery to make a total of 7. I tried to look at the controller to get the model but I'll have to completely remove it to see. The motor is a 36v DC. I wouldn't know how to adjust the charger to get only 40 volts instead of 42 and would it still turn off automatically? That would be ideal as I would have 5 batteries and a little more power. By the way the lights are the only thing that draws 12 volts and are rarely used so it's a non issue.
 
1 - 11 of 11 Posts
Top