Help! solar charging a 36 v 20 ah lifepo4 battery with inverter

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waterbeatsrock
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Help! solar charging a 36 v 20 ah lifepo4 battery with inverter

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.

dogman
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Re: Help! solar charging a 36 v 20 ah lifepo4 battery with ...

Adding power to your battery with any sla charger of the same nominal voltage will work fine. I did about 100 cycles that way with my ping. I belive your 18650 pack has a lower top voltage than ping anyway, which is pretty close to regular sla. For power to flow from the charger to the battery it just needs to be a higher voltage than the pack when the surface charge is removed. For my ping, the packs working voltage is 44v so as soon as I roll a wheel a few feet, the pack is at 44v. Most sla chargers go to about 45v. Those figures are for my 36v pack.

Just use the charger that came with the battery occasionally to fully charge the pack so that the bms will engage in balancing mode. If you slam the pack hard with high discharge rates, and or deep discharges you will need to balance the pack a lot more often, mabye every night. With lighter use, the pack may stay much more balanced. Of course, if just one of the many many round cells in the pack is a stinker, the pack will be perpetually out of balance, and need a good charge every day.

There is allways a lot of interest in this idea from new folks, so if you can, gather some data about how effective it really is, and let us know in a few months.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

waterbeatsrock
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Joined: Thursday, March 19, 2009 - 14:19
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Re: Help! solar charging a 36 v 20 ah lifepo4 battery with ...

Thank you for the reply! I did find a lifepo4 1.8 amp charger on eBay but the ad said that it should be used on battery packs from 6 to 15 ah. I was under the impression that it would work it would just take longer but I assume there is a reason they are limiting sales to a 15 ah max pack. I'm going to be installing an odometer and speed computer so I will happily gather data for everyone interested. It should be interesting as my shirt size is "Oh my it ate Tokyo!!" I top the scales at around 285lbs and the velomobile loaded is heavy as well really the only thing I have going for me is aerodynamics. Ill get a realistic total weight and post my range and specks after foam and paint is applied next week:)

waterbeatsrock
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Joined: Thursday, March 19, 2009 - 14:19
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Re: Help! solar charging a 36 v 20 ah lifepo4 battery with ...

One last question though. If the charger does go to 45 volts does it stay at a constant 1.8 amp? If so I would need 81 watts? Or does the amperage go down as the volts go up? I just don't want to kill the 12 volt as it does power my lights and such.

dogman
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Re: Help! solar charging a 36 v 20 ah lifepo4 battery with ...

yeah, the charger will have to be run intermittently, since it will not run if it has used all the avaliable power in the 12 v battery. I saw your post on the ES, and if I understand right, you will have a panel, charge controller, one sla, an inverter, and the charger for the lifepo4. Even the low output of the charger may outrun the rest of the system. It will take more than one day of power to fully charge the lifepo4. My calculations when I looked into the idea of a solar charging station came up with about 120-180 watts of panel would be needed to charge a 36v sla battery in one day. So to fully charge a ping will take a long time with a smaller panel. But hey, every bit helps.

The charger when first plugged in to a drained battery will put out 1.8 amps at 45 volts. As the battery begins to reach the higher voltage,the 1.8 amps will taper down gradually smaller and smaller till the battery reaches the voltage of the chager and the light turns green. At that point, some current will still flow, but it is very small, and aimed at keeping sla batteries topped up without boiling them away. You will just have to experiment to see how long you can run the charger once the sla battery is full and leave a reserve.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

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