Help! Solar charging a lifepo4 36volt 29 ah battery

[waterbeatsrock]

So I am building a velomobile and I am fine on the artistic side but I was hoping to get a little help from you experts on the charging side as I have all ready paid for the solar panel and charger controller to install and am picking it up on Monday in LA. I bought a battery from Ebay Seller: power_battery_a123 and it seems to be fine even precharged. It pushes the 500 watt 36 volt motor kit I just installed perfectly however the language barrier is a little hard to deal with. When discussing the option of using a 36 volt 1.5 amp charger instead of the 36 volt 3.0 amp charger it came with he was saying it needed voltage in the 40s range and he only carried the 3.0 amp charger. Here are the specks for the battery
Fit 36V Motor Wattage: 400 Watts to 800 Watts, 500 Watts suggested
（if you need high Watts, please email us to advisory )
Voltage: 36 Volts
Capacity: 20 Amp Hours
Dimension: 345 x140x110 mm
（If need other sizes, please contact Me to advisory )
Weight: 9.20 kg
Charging Voltage: <46 Volts
Charging Current: <5 Amps
Rated Discharging Amperage: 20 Amps
Max Continuous Discharging Amperage: 40 Amps
Maximum Discharging Current (Peak): 60 Amps
Lifecycle of the whole pack: >85% capacity after 1000 cycles.
Lifecycle of single cell: >85% capacity after 1500 cycles, >70% capacity after 3000 cycles. (<1C discharge rate and <1C charge rate)

The solar panel I bought is 60 watts I was going to use a sixty watt inverter powered from the load section of the solar controller that would be hooked up to the battery and panel. While driving the panel would run my LCD, and speaker system, lights, blinkers, horn, and such when stopped it would run the inverter powering the 36 volt 1.5 amp (54 watts) charger. The charger that came with the battery says output 36 volts 3.0 amp. I have a 36 volt 1.8 amp charger (65 watts) that came with the amped bikes kit as well so chime in if I can use this with am extra 10 watt panel and a 70 watt inverter. It is called intelligent Battery Charger AA-AK02-3618 it says output 36 volts 1.8 amps and Apply to batteries 36v 20ah to 22 ah. So finally can I use the 1.8 charger or does anyone know where I can find a 1.5 amp 36 v charger that will work with my lifepo4 battery? I'm just about out of money until I sell my 300 mbz veg burner so I would like to start riding asap. Thank you all for your wisdom.

 

[Drunkskunk]

I think you're going to find you rarely get 60 watts out of a 60 watt pannel. pannels are rated by there peak, which means in direct sunlight, at noon, on the equater, on a crystal clear day, aligned perfectly with the sun.

you'll probably hit close to that peak often in LA in the summer, but only when angled directly at the sun.

The other problem is the inverter. they aren't anything close to 100% efficent. Some can do 90%, most are in the 70% range.

a 36V LiFePO4 battery will need something like 43.5 volts to be fully charged.

 

[dak664]

Well, my last poll indicated peak wattage doesn't matter that much to those lifeforms that live more than a few days

Average watt-hours per day per rated PV watt is well documented for every latitude, 4-5 for most temperate zones, and is independent of panel efficiency. Charging efficiency could be 90% if there was a market for such a device.

 

[snowcrow]

You can't connect a solar panel directly to an inverter. You would need a 12v deep cell and a charge controller for it also. A 60w panel would need 6 days (880wh) min. of clear and sunny weather to recharge the 12v deep cell after using the inverter. Two more 60w panels, a 12v deep cell, and a charge controller sould do you for power, but it is not very portable.

LiFePo4 batteries have a very low tolrance to being trickle changed, thus are not able to be charged by solar directly. For that reason I have decided to go with NiCd batteries.

Blessings, Snow Crow

 

[tostino]

Well using a small SLA (8ah or so) as a buffer would be possible, and once the SLA has some charge in it, you could turn on your LiFe battery charger to drain that battery.

You could think of using an RC charger like the Thunder Power 1010c found here: http://rclovers.com/index.htm

This is half off what you would pay elsewhere for this charger.

It's worth some thought at least...

 

[graevus]

I concur w/ snowcrow, you need an energy storage device for the output of the solar panels. I am assuming your power inverter is 12V? 1 or 2 deep cycle 12V SLA's in parallel, or 2 6v's in series. The ones about the size of car battery would be best. What you are doing is storing the trickle of juice coming off the solar panel for until it builds up and gives you enough for a quick charge for the lithium batt when you need it. Make sure the charge controller has some sort of over voltage protection; otherwise your batts will boil from a few days of non-use in LA desert.

Upon re-reading your specs i noticed you plan to ride the bike while charging??? Problem with that is that the bike will use much more juice that is being supplied by the panels, and if you did have enough panels it would be much to heavy and unwieldy for a bike; one wipeout would destroy it all...Maybe with 4 wheels on flat ground, but probably not two. Given the equipment you have already purchased your best option is probably the solar powered charging station; this way you are capturing all the days worth of sun for the quick lithium charge.

You will want a bigger power inverter, 60W is tiny, barely lights a light bulb. The cool thing about this type of system is that with more panels and batts you can actually run your house on it. What would be neat is if you could skip the inverter completely and build the charging system right into the SLA's (you would need enough to make 36V in series). You would also need a good battery management system; lithium takes a pretty specialized charge curve. It would be a custom job, but it could be done. This way you would skip the inverter loss, some are quite efficient, 95%+, others are not.

Anyway, good luck

 

[waterbeatsrock]

Thanks for all the reply's!! To clear up a few points I was not going to charge the 36 volt while riding just the 12 volt 6.5 ah deep cell bb battery that would run my speakers lights video and inverter(used for the 36 volt 1.8 amp charger when not running the motor). I would park somewhere in direct sunlight causing my array lets say between 60 and 80 watts @ 12 volts to power my pwm 12 volt charge controller that has a +-input from array a +- to battery and two direct +- connects for load so the flow of power should go from the panel to controller to inverter excess routed to sla battery for charging. My main question is how do these lifepo4 chargers work? I found a 36 v 1.8 amp (64.8 watt?)lifepo4 charger on eBay but the ad says for 6 to 15 ah battery's (im running a 20 ah). On another fourm I was told that the 36 volt charger runs at 44 volt and then balances the cells so is that actually 44 v x 1.8 amp = 79.2 watt or do the amps go down as the volts go up averaging the same 65 watt draw?

 

[waterbeatsrock]

P.S. Drunkskunk I saw your reply after posting my update thank you food for thought maybe 85 watts array total size for the 1.8amp charger to handle the loss?


tostino I checked that charger out but wasn't it for 24volt max did I read that wrong?

 

[tostino]

P.S. Drunkskunk I saw your reply after posting my update thank you food for thought maybe 85 watts array total size for the 1.8amp charger to handle the loss?


tostino I checked that charger out but wasn't it for 24volt max did I read that wrong?

Nope, i've got the charger, and it's good for 10s lipo... But now that I think about it, I think it's only good for 10s lifepo4 as well.

So that may not work for you.

 

[Drunkskunk]

running the inverter off the SLA, then charging the SLA with the solar pannel might make it work, but you're still cutting it too close with the wattage.

As an example, I have a 2 amp 37volt Lipo charger (output of 42 volts) that uses AC. I was on vacatiion, and bought a 150 watt inverter to charge it up from the car. it didn't work. it wouldn't even power up.

The reason? Although the output was 84 watts, the input needed to be around 125 on the input side of the charger. and the Inverter claimed to be a 150 watt unit, but that turned out to be its total draw. It was pulling 10.5 amps, (my truck's running voltage is 14.6) so the input was 153 watts, the output was below the needed 125 for the charger.

there's a big diffrence in the way they rate these things.

 

[waterbeatsrock]

Bummer, I did find some inverters with over 90 % efficiency but those numbers are a little scary I guess Ill use the solar panel for my cab over and wait for nanosolar to finally start selling to us back yard builders. 200+ watts shouldn't be a problem if I cover the whole body. Ill put a post up next week with some pics when I get back from LA

 

[dogman dan]

I think it will still work, but with a bigger inverter, maybe 300 watts or so? But as I said over on the V, it won't run long enough to charge the lifepo4, unless you have a huge sla. But it will keep the 12v supply going for other uses fine.