Thinking about small solar backup system in South Texas..48 or 24 vdc?

[DonPBall]

So after last Winters debacle down here when the power was out for almost 3 days and the temp got down to 25 degrees about 10 miles from Mexico, I am looking into using the batteries in our golf cart as the battery pack for an inverter to power the refrigerator. The house fridge is 6.5a, but just got a mini fridge rated at 1.1a which might be a better option.

The cart is 48vdc (6 8vdc brand new deep cycle batteries) The batteries are rated at 150 (20hr) 120 (5hr). Thinking of purchasing a decent not too expensive inverter 2000-3000w.

First question: What input voltage inverter....48 or 24 vdc? I could reconnect the batteries to obtain 24 vdc, but would this get me more or less run time? I know the wiring would need to be larger to the inverter with 24vdc. I don't think you can run a 12vdc inverter from 16vdc battery pack and the wiring is again even larger?

Second question: considering some type of portable solar charging system. To charge a 48vdc battery pack I think I would need something like 5 or 6 panels. That's too many to set up temporarily and nowhere to store them. I think the 24vdc system would only need 2-3 panels maybe? Also the charge controller might be cheaper?

i know these subjects must have been discussed here before but I could not find what I was looking for. Thank you for taking the time to read this and possibly supplying more info.

 

[rmaddy]

Do you really have 6 8V batteries and not 8 6V batteries?

Either way you have the same amount of watt hours whether they are arranged into a 6V, 12V, 24V, or 48V battery. So there's no difference between the runtime between any of those voltages. And there's no difference in how much solar you need to recharge. Watt hours is watt hours regardless of the voltage.

You are correct that with higher voltage you work with less amps and can use smaller wire.

I would go with the 48V setup. It allows a bigger inverter if you decide to upgrade. And it allows for more solar if you ever need it.

 

[GXMnow]

I agree. Stick with the 48 volt, that way you don't need to rewire anything, just add an Anderson connector to the gold cart, plug it in when you need it, and still drive it when you don't.

There are several good inverter/charger systems that will work great on a 150 amp hour 48 volt battery bank. Going to 48 volt actually makes the charge controller cheaper. At the same watts, you only need half the amps.

Do an energy audit and see what kind of power you think you will need during a power failure. You need to figure out the maximum power you will want at any given time, and then the total watt hours you will need to make it through a day.

Something like the Outback Skybox might do you well. It can work as a grid tied solar inverter without the battery connected, and when you connect the battery, it can then store extra solar in the battery, instead of exporting it to the grid. You could plug in the golf cart any time, and let the system use it to trim your evening electric bill as well.

 

[DonPBall]

Do you really have 6 8V batteries and not 8 6V batteries?

Either way you have the same amount of watt hours whether they are arranged into a 6V, 12V, 24V, or 48V battery. So there's no difference between the runtime between any of those voltages. And there's no difference in how much solar you need to recharge. Watt hours is watt hours regardless of the voltage.

You are correct that with higher voltage you work with less amps and can use smaller wire.

I would go with the 48V setup. It allows a bigger inverter if you decide to upgrade. And it allows for more solar if you ever need it.

Wow thanks for the quick reply! Yes 6 Crown CR-150 8vdc batteries.

 

[acdoctor]

Be sure to check inverter self consumption it can eat into a small system’s watt hours budget. A generator to recharge?

 

[iamrich]

So, after last Winter's debacle down here when the power was out for almost 3 days and the temp got down to 25 degrees about 10 miles from Mexico, I am looking into using the batteries in our golf cart as the battery pack for an inverter to power the refrigerator. The house fridge is 6.5a, but just got a mini fridge rated at 1.1a

I would be (was) more worried about heat, as our house got down into the 40's (inside) during the same event. Never once worried about the fridge.

 

[DonPBall]

I would be (was) more worried about heat, as our house got down into the 40's (inside) during the same event. Never once worried about the fridge.

We have small propane heater and camp stove so heating and cooking are covered. Just looking at the refrigerator idea since we have the golf cart batteries available.

 

[DonPBall]

I agree. Stick with the 48 volt, that way you don't need to rewire anything, just add an Anderson connector to the gold cart, plug it in when you need it, and still drive it when you don't.

There are several good inverter/charger systems that will work great on a 150 amp hour 48 volt battery bank. Going to 48 volt actually makes the charge controller cheaper. At the same watts, you only need half the amps.

Do an energy audit and see what kind of power you think you will need during a power failure. You need to figure out the maximum power you will want at any given time, and then the total watt hours you will need to make it through a day.

Something like the Outback Skybox might do you well. It can work as a grid tied solar inverter without the battery connected, and when you connect the battery, it can then store extra solar in the battery, instead of exporting it to the grid. You could plug in the golf cart any time, and let the system use it to trim your evening electric bill as well.

The Skybox is an excellent option, but way out of our price range. Just trying to put something together just in case. Of course the governor here just said this won't happen again...so now I am sure it will!

 

[iamrich]

We have small propane heater and camp stove so heating and cooking are covered. Just looking at the refrigerator idea since we have the golf cart batteries available.

If we have another snowmageddon, just push the fridge outside... :D

 

[Supervstech]

Refrigerators consume very little energy…
If that is your main concern, 24V setup should be fine with a pair of 100W panels… maybe 3…
Make a list of what you realistically want to power, and for how long…
If the watthours of that are over 1200Wh a day, more panels would be needed.

 

[DonPBall]

If we have another snowmageddon, just push the fridge outside... :D

Well now that we have the little mini fridge located in the shop which is attached to the house but unheated...no need for any pushing it outside! Going to buy the inverter soon and see what operating time the golf cart batteries can provide.

 

[DonPBall]

So found this inverter that we might buy to power the mini fridge.

Amazon.com

Along with a Bussmann 70a circuit breaker and 3' L #2 cables.

Any commnts? I know it's a cheap Chinese inverter but don't want to invest a ton of money either.

 

[HRTKD]

That inverter's specs look OK. But, like you said, it's a cheap one. The circuit breaker is the appropriate size and as long as it's a real Cooper Bussmann it will work well.

 

[DonPBall]

So I have the inverter and circuit breaker now but in a quandary. The Bussmann 70A circuit breaker has a label on it stating 48vdc MAX. The golf cart battery bank fully charged is 49-50vdc. Did I get the wrong circuit breaker?

 

[HRTKD]

So I have the inverter and circuit breaker now but in a quandary. The Bussmann 70A circuit breaker has a label on it stating 48vdc MAX. The golf cart battery bank fully charged is 49-50vdc. Did I get the wrong circuit breaker?

That circuit breaker is out of spec for your use. For a Trojan 8 volt battery in a 48 volt system, the float charge alone should be 54 volts. The equalization charge can be up to 64.8 volts.

https://www.trojanbattery.com/pdf/datasheets/T875_Trojan_Data_Sheets.pdf

Where in your system were you planning to place that circuit breaker?

 

[DonPBall]

That circuit breaker is out of spec for your use. For a Trojan 8 volt battery in a 48 volt system, the float charge alone should be 54 volts. The equalization charge can be up to 64.8 volts.

https://www.trojanbattery.com/pdf/datasheets/T875_Trojan_Data_Sheets.pdf

Where in your system were you planning to place that circuit breaker?

Between the batteries and the inverter.

 

[HRTKD]

Between the batteries and the inverter.

That's what I was afraid of. Besides the voltage, the breaker is marginal on amperage. 75 amps is better.

2500 watt (AC output) / 48 volts / .85 (inverter inefficiency) * 1.25 (to avoid nuisance trips) = 75 amps.

The use of 48 volts in the calculation is (hopefully) worst case. Normally your voltage won't dip that low, but just in case it does, you're covered.

 

[DonPBall]

That's what I was afraid of. Besides the voltage, the breaker is marginal on amperage. 75 amps is better.

2500 watt (AC output) / 48 volts / .85 (inverter inefficiency) * 1.25 (to avoid nuisance trips) = 75 amps.

The use of 48 volts in the calculation is (hopefully) worst case. Normally your voltage won't dip that low, but just in case it does, you're covered.

Thanks for the quick reply. Can't find any breakers rated for more than 48vdc. Can I just use some type of fuse?

On a positive note:. The inverter was not made in China! Check it out! Don't know where Chian is though.

 

[HRTKD]

Breakers only go so high in amperage before they start to get stupid expensive. At that point, most people switch to fuses. I'm using a MEGA fuse on my inverter. It's what Victron has in their diagrams, so I'm going with that.

 

[Hedges]

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

I think all those are 10k AIC. That should be enough for short-circuit current of lead-acid batteries.
Some are polarized, which should be OK for battery to inverter (not bidirectional)