Solar panel charger for RC model car batteries

[Mike90250]

1) Summer Solstice, you might get 6 hours of usable sunlight. More likely you will have 4 hours by them time you factor in poor alignment (aim) and some cloudy conditions

2) Adding 20% contingency: 48 x 1.2 = 60 watt panel
nope, more like 80% contingency is the realistic value.

[Goatee]

Based on the helpful comments and advice, this is what I came up with for sizing my project. Comments??


Size system to recharge four 12V 3000mAh RC batteries
4 x 12V x (3000mAh/1000) = 144 wh
Size solar battery for twice the load: 2 x 144wh = 288 wh
Converting to ah : 288 wh/12 V = 24 ah solar battery
Need to replace 288 wh in solar battery with 6 hours of sunlight
288 wh/6hr = 48 watt solar panel
Adding 20% contingency: 48 x 1.2 = 60 watt panel

[Goatee]

Understood. That's what I meant to say but it did not come across that way. Pardon my struggle with words (among other things)

[Goatee]

Understood. That's what I meant to say, but it didn't come across that way.

[Mike90250]

Solar is NOT going to recharge RC packs. Most solar controllers are 12V, 24V, 48V. Nothing that would cover a 7.4v rc pack. You use the solar to charge a 12V battery and then use a 12V charger adapter to charge the 7.4v RC pack.

[Goatee]

Thanks! I need to tweet your example for my application. For instance, the controllers for these little cars use AA NiCads and I will not recharge them. It's a great start for me. What is the corresponding solar panel sizing for your example? How does the length of a charge cycle I can accept enter in to the calcs. Right now it looks at least 4 hours would be OK to recharge two 7.4V 3000mAh packs.

[Mike90250]

Size the "battery" to be 2x the daily cumulative total of what your RC gear burns. And you do it in WATT Hours

if you consume 6 pack changes, of 6V 4ah, that's 6x4=24watt hours each, 6 cycles would be 144wh
and don't forget the controller packs, 9V 3ah = 27wh x 3 charges = 81wh
81 + 144 = 225 wh per day. So your big battery needs to be 2x that, 450wh. It's at 12V so a 37.5ah battery would be about right.

Volts x Amps = watts
Watts x Hours = Watt Hours wh
WH / V = amps

Have at it.

The solar recharge will be mostly inconsequential and I'm ignoring it. By the time you factor clouds and mis-alignment 100wh of contribution would be outstanding, But it is a learning tool

[Goatee]

Like I said I'm just getting started. With stuff from the Amazon web site, my first stab was a solar panel going to a EEKit controller to a 12V battery. From there 12V to a Tenergy balance charger to the RC battery? Am I anywhere close to a workable system? Next step I see would be sizing the panel and the 12V battery.

[SunEagle]

I'm on the learning curve with sizing the components I need for my application. Once that gets sorted out I should know if what I want to do is feasible. I hope I can find a way to make it work. I appreciate your advice.

Take a look at AGM or maybe Optima batteries and then determine the solar panel wattage you need to keep the battery happy.

I would think your RC car batteries can be charged by an 8 amp or less charger but that is something you need to determine how many watt hours it will take to get them back up to full.

[Mike90250]

Think of how you will package it. A milk crate works well as an organizer. Battery on one side, PV charge controller can zip tie to other side. use an Anderson Connector to provide EZ connection of the solar cable. Panels much over 100w, start to get bulky and cumbersome to store, pack and move. You will need some sort of tripod or stand for the PV panel to sort of aim it close to the right direction.
Will your charger run off 12V or do you need an inverter to provide 120VAC for the RC charger ?

[Goatee]

I'm on the learning curve with sizing the components I need for my application. Once that gets sorted out I should know if what I want to do is feasible. I hope I can find a way to make it work. I appreciate your advice.

[SunEagle]

The system should be portable for off the grid locations. My immediate use would be for charging batteries in RC cars when camping. I realize buying some spare batteries or charging off of the car battery would be cheaper, but I want to use it as a means for the grandkids to learn how a solar energy system works. I want to also use it as a demonstration and education device for older folks as well.

I understand your desire to have a solar/battery system. My caution is not to purchased a "package" like they sell from Yeti or some other solar power system. It will actually be cheaper to build it yourself once you know what battery to get and then you match 10% of the battery Ah rating to the panel Imp rating.

Like I said I built mine about 5 years ago when the folding solar panels were very expensive. That consumed about half of the total $550 that I spent. The Optima battery cost almost $175 back then as well. The battery box, inverter and luggage carrier made up for the rest of the cost for my system but back then a similar "package" was going for about $1000 and had a smaller battery installed.

[Goatee]

The system should be portable for off the grid locations. My immediate use would be for charging batteries in RC cars when camping. I realize buying some spare batteries or charging off of the car battery would be cheaper, but I want to use it as a means for the grandkids to learn how a solar energy system works. I want to also use it as a demonstration and education device for older folks as well.

[Mike90250]

From my model plane racing days with large 1/4 hp glo-plug engines, we had a dolly rigged up with a car battery and a starter motor with a rubber insert on the shaft, which got jammed into the prop spinner and the plug and motor were powered by the battery. Hardest part was lifting the battery out of the trunk and setting it on to the dolly.

A PV panel large enough to provide meaningful recharging in the field, will be so large, it would be unwieldy. So, in my opinion, a sealed AGM battery (not Gel, which must be trickle recharged), in the 50ah ballpark, would be a fair size to get a half dozen or so recharges in the field. Then you need a pack charger that runs off 12V, which you would need anyway.

[azdave]

Ah yes. I remember charging LiPo's using a repurposed CC/CV power supply running on an inverter under the hood of the car back when we did 2-3 day long R/C shows around the US. We first flew LiPo batteries back in early 2002 when many dedicated R/C LiPo chargers were still being developed.