Have 275 watt panel, what to use for RV battery charging

[BearhawkLSA]

I was given a couple of Solarworld SW275 mono panels. They are 30 volt / 9 amp panels. I want to use one for charging the battery on my camper. Any suggestions on a charger? I currently have a single battery on the camper but am considering adding a second.

Dave

[Mike90250]

If use use a cheap $80 PWM controller, you will harvest 120W from the panel, or with a $300 MPPT controller, you would get the full 275W. Free solar power is not cheap ! Either way, the panel can only produce 9A, the MPPT can transform that into full power into the battery,
hint - most cheap $50 mppt controllers on fleabay are fraudulent, being re-labled PWM controllers.

[Enough2Bdangerous]

To that point what mppt controller would you recommend, and from where would I purchase it? Thank you

[Sunking]

Assuming 12 volt battery as that is your only option, it has to be a MPPT Controller, a real MPPT controller. At 275 watts means at least a 20 amp Model. Look at something like a Blue Sky 2512i or Morningstar PS25.. Do not under any circumstances us PWM Charge Controller or use anything less than $175. Anything less than $175 at 20 amps is a CHI-COM POS fake PWM controller.

Hold off on adding a second battery. Better option is replacing the battery you have. A 275 watt panel on a 12 volt battery will support up to a 200 to 150 AH battery. That is larger than any 12 volt battery you can buy. That is the world of 6-volt Golf Cart batteries like a pair of Trojan T-105 or T-105RE a 6-volt 225 AH battery wired in series for 12 volts. You DO NOT WANT PARALLEL BATTERIES. Let your neighbors and friends make that mistake. But not with your money.

[Enough2Bdangerous]

Apologies for the post above. I see your recommendations here

[BearhawkLSA]

I hadn't considered swapping to a pair of golf cart batteries. Paralleling batteries is a pain with balance problems.

My big concern was if I went MPPT I would have the potential of pumping 25+ amps into the battery which would be a pretty high rate to sustain on a lead acid. I do understand that sustaining close to 100% output would be rare - I have a 10.4kw grid attached system on the house and have seen that vary between 1kw and 10kw output in a matter of minutes.

I did some measuring and can weld up a nice carrying bracket that will sit between the spare tire holder and the back of the trailer.

Dave

[Sunking]

My big concern was if I went MPPT I would have the potential of pumping 25+ amps into the battery which would be a pretty high rate to sustain on a lead acid.

What concern? 25 amps would be to much for AA batteries, but we are talking 225 AH batteries where 25 amps is perfect, and they can take even more. Lead acid batteries have a minimum and maximum charge current they can handle. The window is C/12 on the low side, and C/8 on the high side. C/10 is perfect. Where C = battery AH capacity. So for 225 AH / 10 = 22.5 amps. You should only be concerned if the minimum 19 amps is not met.

Keep in mind if a battery is charged up, it does not accept any more current.

[BearhawkLSA]

What concern? 25 amps would be to much for AA batteries, but we are talking 225 AH batteries where 25 amps is perfect, and they can take even more. .

Concern was with the current battery on the camper. It is 80 or 100 ah so I would be pushing up around C/4 at full output.

Dave

[Sunking]

Concern was with the current battery on the camper. It is 80 or 100 ah so I would be pushing up around C/4 at full output.

Still not a problem, you need a battery replacement. The higher charge rate means high water use and some heating. Keep an eye on water levels until you replace the battery.

With that panel at 12 volts, you are going to need a 200 to 300 AH batteries. The reason 6 volt batteries escaped you is because you are trapped in a 12 volt toy box. Batteries are 2 volts, not 12 volts. Toys use 12 volts.

Now if you can find a 12 volt 250 AH Deep Cycle battery have at it. But good luck finding such a 150 pound beast. Look for 6 volt 220 to 250 AH batteries. You will need two of them. The best are Trojan T-1005 RE followed by Trojan T-105. The T-105RE is a 4 to 5 year battery, the less expensive T-105 is a 2 to 3 year battery which makes it the most expensive of the two options.

[Mike90250]

re batteries. the cheap end is 6V golf cart batteries 6V 220A roughly, last 3-5 years, and are easy to find, and cheap.

Charge Controllers
Morningstar makes some great MPPT controllers, as does Midnight Solar

http://www.morningstarcorp.com/products/prostar-mppt/

http://www.midnitesolar.com/pages/kid/index.php

http://www.midnitesolar.com/images/frontPage/PSvsKID.pdf

Check out the prices and accessories needed for each, what sort of monitoring you want.

Firmware, updates have always been easy and reliable with my Morningstar products, not so much with Midnight. If you
don't want to mess with updates, ignore this.

[BearhawkLSA]

There are some cheap open box Renogy 40 amp MPPT controllers (RE-CRTL-MPPT40-F) that they claim are factory refurb and tested. Worth looking at or run away? I don't see Renogy in any of the suggestions above.

Dave

[BearhawkLSA]

Following up with what I ended up doing.

I decided to cheap out a bit because the panels will be used 2-4 weeks/year and in storage the rest of the time. After looking around I found the EP Tracers and that led to their newer series the EPEver. $130 at Amazon got me an EPEVER 20A MPPT Solar Charge Controller Tracer A 2210A + Remote Meter MT-50 Solar Charge With LCD Display. That should let you find it on Amazon. The ratings were OK but the shipping packaging was minimal. I added a cheap set of 10 gauge Harbor Freight jumper cables to go from the controller to the battery (cut off one end). They are 10 gauge aluminum so should handle up to 20 amps with no problem.

The programming let me set it to match the camper battery - flooded 85ah.

The panel is leaning on the camper and making power. The numbers coming out indicate that it is MPPT and not PWM.

Next step is to stop by the hardware store and pick up some light chain to put kick stands on the ends of the panel and pick up some decent connectors to let me plug the panel into the controller instead of using the screws. I will also pick up some wire to give me more distance to the panel.

Because the panel was free I will end up at less than $150 for the project and not have to listen to the generator run (except to power the microwave).

Dave

[Mike90250]

With using the aluminum jumper cables, you HAVE to use hydraulic crimp and aluminum rated lugs. Otherwise, we will see your camper listed in the fire reports under aluminum wiring electrical fires. VERY SERIOUS business,

For the Quick Connects, look at Anderson Connectors, they are common, reliable and easy to use.

[BearhawkLSA]

I went looking for the Anderson's and none in the area. I will need to do a mailorder.

Not too worried about the crimps on the aluminum. It is a set screw connection on the charger and a battery clamp on the other. Just clip it on to the battery at the campsite, nothing permanent or enclosed.

Dave

[Mike90250]

sometimes the RC hobby shops carry them for quick battery pack swaps, just make the size is good for your PV amps