Needing battery expert to help me figure out my system

[Jasper7821]

first let me say thank to everyone on this site who has helped me with questions. My Focus buyback is complete and they put me into a new F150. The whole process took less than 30 days.

If anyone knows about battery banks and charging and can assist or let me know a forum that could help me out.
I'm building a mobile Gelato trailer and trying to build a battery bank system and looking for battery/install advise.
Everything in the trailer is on 110v and it pulls about 30 amps if the AC is running. in the summer the AC will be on all the time and the winter maybe 1/2 the time.

The inverter I was going to use is pure sine 4kw and has a surge of 12kw for 20 seconds so it should be ok if all the compressors happened to kick on at the same time.
http://www.aimscorp.net/4000-Watt-24...r-Charger.html

I was first going to use 12v AGM batteries but I think I can save money with 6v lead acid golf cart batteries and have a compartment built next to the generator box.

I'm not sure my math and conversions are right: One battery is 225ah x 6v = 1,350 watts / 120v = 11.25 amps and if used 75% drain = 8.4 amps. ? ? ?

So if I had 8 batteries that would be 67.5 amps at 75% drain that would give me 2.25hrs if the AC was running full time?

I have a really quiet Yamaha 4.5kw generator and it has one 3 prong 110v 30 amp outlet, and two 20 amp household outlets.
I was thinking of using the 3 prong plug for generator power and unplug that at night and plug it into shore power to charge the batteries. At night with the Gelato case and fridge closed, there shouldn't be much amp draw at all and hopefully the batteries can fully charge overnight.

If anyone has suggestions, WIRING DIAGRAM, or advise or a better way of doing this please let me know.

Thanks

 

[davideos]

I think you are on the right track. Just be sure to do all you calculations when the batteries are not at full capacity.

Also, if you need 12kw for if everything kicks on at the same time, that is 100A at 120V. Not counting for the inefficiencies of the inverter, using 6V in parallel at the inverter input, you will need 2000A from your battery. Suppose you had 10 six volt lead acid batteries to make math simple, you will require 200A from each. Pulling 200A from a battery will cause the voltage to drop. How much is dependant on the battery. If it does drop, will it still meet the input requirement of the inverter? But also note that if the voltage drops, more current will be needed to meet the 12kw surge.

Anyway, just some things to think about.

 

[davideos]

The other problem is your capacity. In the summer, you will ne 30A at 110V constantly, or 3300W. However, you mentioned the batteries were 225Ah at 6V; which is 1350W. With 8 of these batteries, you could run your trailer for 3.2 hours...and that assumes that you can pull the whole 225Ah's out at a voltage that the inverter will still run at. Batteries will have a curve. As they discharge, the voltage will drop. Batteries also have internal resistance, which causes the voltage to drop when you draw more and more current. So what you need to do is look for a datasheet on the battery and look at what the voltage is under various load conditions. In this case...again, not looking at the inefficiency of the inverter...you will need more than 68.75A from each battery to give your 3300Ws, so with your batteries under this load, what is the voltage output? Will the inverter still run at that voltage. Next question is, for how long? As the charge depletes, the internal voltage of the battery does also. Couple that with your internal resistence, how long will the battery deliver power before the combined voltage dip will no longer run the inverter?

 

[Jasper7821]

Things are even worse than I thought. I talked to a battery guy and he said I should only run the lead acid batteries down to 50%. That won't even give me two hours with the AC running and I didn't factor in the inverter amp draw and battery inefficiently. So maybe I'd only get 1.5hrs with the AC on. It's close to winter and it's still 85 degrees here so I think I'd be using the generator most of the time.

I'm starting to think that it would be more efficient to ditch the battery idea and sell my 4.5kw generator and get a 6.5 or 7kw generator and just run it all day.
I would like some kind of backup for the gelato case in case the generator had a problem. If the drinks in the fridge got warm that's ok, but if the gelato melted then it's all wasted.

 

[jeffand]

Battery manufactures rate the amp hour rating over 20 hr dischage period. If the battery is discharged at faster rate the amp hour capacity of the battery is reduced.
Power inverters produces power from DC source. This typicaly is a battery bank voltage of 12 volts, 24 volts, and 48 volts. Now not all power inverters are created equal. What you should look for is a true sine wave inverter, not a modified sine wave inverter. The battery bank will also need to have a DC rated cicuit breaker to shut the system down incase of a fault.

 

[Jasper7821]

Battery manufactures rate the amp hour rating over 20 hr dischage period. If the battery is discharged at faster rate the amp hour capacity of the battery is reduced.
Power inverters produces power from DC source. This typicaly is a battery bank voltage of 12 volts, 24 volts, and 48 volts. Now not all power inverters are created equal. What you should look for is a true sine wave inverter, not a modified sine wave inverter. The battery bank will also need to have a DC rated cicuit breaker to shut the system down incase of a fault.

Thanks, the inverter I'd get is a pure sine wave one with 12,000 watt surge.
I think I've gone back to my original idea I had and run the AC with the generator and the rest of the trailer on batteries. I think that will take me down to 10-15 amps and would get about 3 hours on battery.

 

[davideos]

At 15 amps at 110, you're looking at 1650W. Assuming your inverter is around 90% efficient, we'll say you need 1833W out of your 8 batteries...assuming again, 6V. At 6V, you will need a total of 305A. Divided by 8, that's 38.2A. So check your inverter document and find out what the minimum input voltage is and then check what the internal resistance of the battery is and the voltage at various states of charge. Looking at a 12V battery from power-sonic that I happen to have...it is a 210Ah battery. At 40A, it will dip below the 12V line after about 1.5hrs at that rate. It will drop to 11V after 5 hours. I don't know what your 6V batteries are, but the data sheet should supply you this information.

Good Luck.

 

[jeffand]

I would would recommend going with a 24 volt battery bank. This will drop the current draw in half when you double the battery voltage. You could go with two parralle strings of four golf cart batteries. With configuration the inverter should draw about 76 amps with a 1650 watt load on the inverter. Out of each string of batteries the current draw should be a bout 38 amps. This will give a maximum run time of about 5 hours. Power inverters draw power even nothing is using it's power. I would invest in a "Kill A Watt" meter and acually test how much power you really need over a 24 hour period.

 

[EVA]

Don't know if this would help you. There was a simple page on how to do the battery size calculations. Granted it is for sump pumps, but something tells me this could scale.

http://www.tripplite.com/shared/literature/White-Paper/How-to-Select-Inverter-for-Sump-Pump-White-Paper.pdf

 

[Jasper7821]

Thanks everyone, i really appreciate the advice.
I'm going with eight Trojan T105 6v golf cart batteries and make them into a 24v system. The batteries and pre-made wire is just over $1,100
I'm hoping it all works out.
The AC will run on the generator and the gelato case, fridge, water heater, and inverter will pull about 15 amps.
I calculate 5,400 watts if I take the batteries down to 50%. That should give me 3 hours until I need to start the generator.

Here's my drawings if anyone is interested and has advise.
The wiring I copied from what an RV shop drew out. I hope it's all correct.

 

[Jasper7821]

Don't know if this would help you. There was a simple page on how to do the battery size calculations. Granted it is for sump pumps, but something tells me this could scale.

http://www.tripplite.com/shared/literature/White-Paper/How-to-Select-Inverter-for-Sump-Pump-White-Paper.pdf

Thanks, this is a great read.

 

[jmueller065]

I would highly recommend using LED lights throughout the trailer for your lighting needs--for both the 12V lights and the 110V lights.

They will probably reduce the current draw for lighting enough that you could neglect it in your power calculations.

(I replaced all the 12V pancake lights in our RV with these LED ones:
http://www.campingworld.com/shopping/item/double-pancake-led-light-fixture/55018
When I did the replacement I measured the current draw of the old vs new light fixtures, it came out to:
5 LED fixtures = 1 traditional fixture)

I know the power draw from all the refer's and the A/C will dwarf the draw from any of the lighting--but every little bit helps.

 

[jeffand]

First thing I would do is try and do is reduce the power usage. For lighting try and use compact florescent, or LED bulbs. They reduce your your lighting load by 60 to 80 %. Power the air conditioner with the generator only. As for the generator operation and installation a number technical and saftie issues come into play. Such as fuel storage and proper ventlation. If the generator is going tobe opperated from the storage compartment you will a generator that is designed for this type of installation. These types of generator are typically installed in a RV. Consult the manufactures recomendations as to the propper installation methods.

 

[EVA]

Jasper - glad that white paper was helpful.

I'll third the recommendation on LED's for lighting. Compared to incandescent, no heat - so in the summer, you have a little less heat to worry about. They last forever. I'd encourage LED over CFL from a breakage standpoint. If you break a CFL, you have mercury to to worry about. Around food, mercury is a really bad idea.

You can also buy LED replacement bulbs and it looks like camper / RV fixtures here:
http://www.superbrightleds.com/
(the one wedge type replacement bulb at camping world for $24 sure seemed expensive)

 

[Jasper7821]

Thanks, this trailer I'm having built is going to have a retro look and I don't want the standard concession look with fluorescent lighting.
I was going to use 3 of these Home Depot vapor lights http://t.homedepot.com/p/Lithonia-Lighting-Flush-Mount-Vapor-Tight-Incandescent-Light-Fixture-OVT-150I-120-M6/100652873/
They use 150 watts each and hope that's not too much.
I've looked at the superblightled site a few months ago and was going to use LED panel lights but my fiancé thinks it looks better with the vapor lights. We were also going to try mason jar lights. I wish I could find cool retro looking LED lights.

They also sell a regular looking light bulb that I think is LED and it's got a rubber gel on it so it it ever broke it all stays in one piece. Really cool bulbs and they're about $15 each.
Kinda like this. http://t.homedepot.com/p/Cree-9-5-Watt-60W-Soft-White-2700k-Dimmable-LED-Light-Bulb-E-BA19-08027OMF-12DE26-2U110/204592770/

 

[Jasper7821]

All the trailer lights are LED except for the two 12v dome lights that the trailer comes with. But there's a separate small 12v battery on the tongue.

 

[EVA]

The vapor tight fixture is a great thing to use. I wouldn't put an LED bulb in there. LED's are very sensitive to overheating, and that fixture has no air flow to allow the lamp to cool.

Regular looking LED's are getting more common. Cree is really popular among the LED afficianados. For some reason they see that brand and go crazy. G7 Power is a company that makes less expensive lamps that look a lot like standard bulbs.

http://www.amazon.com/G7-Power-G7A191029-9-5-watt-4-Pack/dp/B00CYSA6FK

 

[Jasper7821]

Thanks for the link and info on the LED bulb heat. Ya since there's a thick glass enclosure I'd need something that won't overheat.

I'm hoping three of those vapor lights will be bright enough in the 14'x8' trailer.

 

[jeffand]

One of things people need to consider is more watts does not mean more light. You have to have to look at the light ouput in lumins. More watts the sooner you have a dead battery.