Golf Cart Batteries and Inverters

[BigRich]

Hi from Florida. I recently moved into a new house and with Irma headed this way have been forced to try to figure what to do if we lose power for a few days.

I have a 48 volt golf cart with (8) US 12V batteries. They are 77 minutes at 75 amps. I also have a 3,000 watt very loud generator that I don't want to run while we're trying to sleep.

I'd like to use the batteries if we lose electric to power my portable ac units, refrigerator, and freezer, while we're sleeping. Then during the day, I'd like to run the generator to charge them back up. The two ac's, fridge, and freezer use 2,755 watts.

Do you think this is a good idea or is there another way I should be approaching this? I'm trying to avoid dropping a few thousand on a Honda generator.

[BigRich]

US Battery tech support says the batteries will last between 3 and 4 hours if I use 3,000 watts continuously. Of course the freezer and refrigerator won't run all the time and I would hope the a/c's will shut off after a couple of hours as well. So possibly that run time could double or even triple especially if i can cool the rooms down using the generator before I switch over to batteries. Which inverter would I need to be using?

[SunEagle]

US Battery tech support says the batteries will last between 3 and 4 hours if I use 3,000 watts continuously. Of course the freezer and refrigerator won't run all the time and I would hope the a/c's will shut off after a couple of hours as well. So possibly that run time could double or even triple especially if i can cool the rooms down using the generator before I switch over to batteries. Which inverter would I need to be using?

IMO I would think about using fans to keep cool at night then using A/C. Unless that A/C unit is very small it will eat up the batteries quickly.

I just tested my 2 generators and topping off my small battery system. I also live on the West coast of FL around the Clearwater area. My guess is that we could lose about 2 days of power if we get even a close call from Irma.

[AzRoute66]

Whether it is Irma or not, now that you are thinking about it, seems a great time to get to know a Kill-A-Watt meter. Put it on the fridge and freezer for a week and get an accurate hourly average that will include the duty cycles, start-ups, etc. You can also measure your major hard-wired appliances by timing the digital (or mechanical) 'spinner' on most electrical service meters. I would bet you will be pleasantly surprised to find that your fridge and freezer are using a good deal less than their rated wattages.

[BigRich]

Thanks. The a/c's that I bought are for two rooms, the master and guest room. The larger unit draws 900 watts and the smaller unit draws 450 watts. Both units are sized for the room they'll be in. I need the a/c to sleep. Fans won't do it for us. If I have to I'll just run the generator all night.

[BigRich]

I just Googled 3,000 watt 48 volt to 240 volt inverters. Holy cow they're expensive. $1,000. I don't see me buying one of those. It's too bad. I have all of these batteries and no other way of putting them to use.

[Mike90250]

You can still run a smallish inverter for some lights and outlets. You will need a Transfer switch to connect gear to the generator, Fill your cars up, store some fuel (takes a lot of time to replace torn down power poles, and all the crews are in Tx) and hope flying debris does not do you in.

[BigRich]

Does anyone know how many watts 150' of #10 wire is rated for?

[Mike90250]

Not rated in watts. #10 wire is safe at no more than 30 amps. The lower your voltage, the more your losses will be.

[SunEagle]

Does anyone know how many watts 150' of #10 wire is rated for?

Most #10 awg wire is good for about 30 amps depending on the insulation type and how it is being run (open air, conduit, direct burial, etc.)

The problem is the voltage drop at 150feet. So what voltage are you using for that #10 wire.

[BigRich]

It's generator power. 120/240v. It's THHN and will be laying on the ground and in the wall.

I asked about the wattage because when I did my load calculation it was in wattage so that I knew what generator I needed. I wasn't paying attention to the amps unfortunately.

[BigRich]

It looks like this generator can handle 41 amps which isn't good because my wire can't. It's back feeding my panel through the dryer breaker which is a 30 amp but because the voltage is moving the opposite direction through the breaker I don't think I can trust it to trip.

Generator:
5000 watts
power factor 1
duty: continuous
voltage 120/240
amps 41.7/20.8

[sensij]

It looks like this generator can handle 41 amps which isn't good because my wire can't. It's back feeding my panel through the dryer breaker which is a 30 amp but because the voltage is moving the opposite direction through the breaker I don't think I can trust it to trip.

Generator:
5000 watts
power factor 1
duty: continuous
voltage 120/240
amps 41.7/20.8

Whoa, slow down.

The 30 A dryer circuit is probably 240 V. Does it include a neutral, or is it just two hots?

You need to be careful here. If you are going to back feed through a load circuit like this, you need to make sure your main breaker is off first. The load breaker is probably bidirectional, at least, although you should still double check.

The voltage you back feed needs to match whatever the existing circuit was providing. If you try to put 120 V from the generator onto a 240 V circuit, you are going to have problems. If your generator's 240 V output is not split phase (three wire output), you would not be able to use it to power 120 V loads.

What specific generator model are you using?

[BigRich]

It's a 4 prong outlet that you can plug in a nema 14-50p plug into. It's got two hots, a neutral, and a ground. So does the generator. The generator says single phase. It's a Coleman Powermate 6250.

http://www.powermate.com/pdfs/2007/11/17/manual_pm0525202.03.pdf

I have another generator but it's also single phase and only 3000 watts. So I guess you're saying all of my 120v breakers won't work?

Do you know if square d QO breakers are bidirectional?

Thanks for letting me know about the safety concerns. Turning the main breaker off is the first step when setting up and the last step when tearing down. Also never touch the plug at the dryer outlet while the generator is running.

Thanks for your help!

[sensij]

Simple QO breakers (no suffix in the part number) are bidirectional.

The 4 prong outlet on that inverter can only supply up to 20 A. You'll be ok with #10 wire. It looks like it will do what you want it to do, providing the 120/240 V output that will power your 120 V loads and your 240 V loads.

You can supply up to 5000 W through all three outlets, but no individual outlet may supply more than 20 A.

Perhaps someone with more generator experience will jump into the thread with any other suggestions.