Golf Cart as supplimentary battery bank

lairdreed

I am interested in having a 48v golf cart tied into a battery backup grid tie system I'm designing for my house. The batteries would be used to augment a smaller but permanent 48v bank of the same type of batteries when parked and then I could run around in the cart on weekends. Is this possible or would mixing the batteries with different usage profiles hurry the end of all batteries and hooking up a dead gold cart to a full bank of other batteries melt the wires inbetween? Is there a smart way to do this?

Good material in this forum, thanks to all of the experts...

Laird

icarus

Re: Golf Cart as supplimentary battery bank

There is probably not a very good way to do this.

If both batteries are of a similar chemistry, size and type it is do-able, but if you are going to discharge the golf cart on a regular basis, but don't discharge the "house batteries" they probably won't play well together.

A simple alternative would be to install either two controllers in a parallel system, or install a "A"/"B" switch system, such that you can charge each bank separately. When it come time to use the system for emergency power, you could wire them both to feed the loads either as one large bank, or two smaller ones.

Tony

Peter_V

Re: Golf Cart as supplimentary battery bank

lairdreed wrote: »

I am interested in having a 48v golf cart tied into a battery backup grid tie system I'm designing for my house. The batteries would be used to augment a smaller but permanent 48v bank of the same type of batteries when parked and then I could run around in the cart on weekends. Is this possible or would mixing the batteries with different usage profiles hurry the end of all batteries and hooking up a dead gold cart to a full bank of other batteries melt the wires inbetween? Is there a smart way to do this?

Laird

Well, there are a couple ways to do this. You could use relays and diode, etc. to charge/discharge the two battery packs separately. Might take a bit of work to get the system to switch from one battery to the other without a power glitch when running from batteries.
While more complicated, this is probably the better route to go for battery longevity.

Or you could just connect the GC directly to the house batteries when you're done using it. If they are at significantly different charge states this will cause a rather large current flow as the higher charged battery dumps into the lower one. Probably in the hundreds of amps initially.
If you go this route, I'd recommend a large frankenstein switch (knife switch) located away from any batteries (outside is best) to avoid igniting any hydrogen that might be floating around.
The batteries will wear out at different rates which will likely diminish the life span of the house batteries. Connecting batteries like this tends to beat down the stronger ones until the match the weaker.

Another option, if your inverter allows it, is to forgo the house bank and just use the GC batteries. Sure there is a chance that you'll have a power outage while the GC is not connected, but you'll probably notice that and can quickly reconnect and restore power.
This is the simplest solution by far.

Note, unless you spend a fortune on batteries, you won't have enough backup power to last very long anyway.

techntrek

Re: Golf Cart as supplimentary battery bank

Since they aren't exactly the same - age, size, manufacturer, etc. you must charge them separately. If you were going to use this off-grid every day you would also have to use them separately using the A/B switch icarus mentioned. However, for occasional emergency back-up using them together should be fine.

The reason is one of the two will age prematurely if they are always charged and used together but aren't exactly identical. Since one is on a golf cart this is probably not an issue, you'll charge that one from its own charger once the grid is back up.

Photowhit

Re: Golf Cart as supplimentary battery bank

If the golf cart will not be used regularly, you might use it as a 'dump' load, You would need a charge controller typically used for wind gennys. This would first charge your homes batteries then 'dump; or devert the charge to the golf cart batteries.

I've never use one, but I think typically the charge is sent through ungoverened typically to a resistance load like a water heater, so a second charge controller would be needed.