How to 500W Charging?

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JKO

Member
Joined
Dec 5, 2013
Messages
24
Location
Falsled Denmark
I have a used forklift battery that is charged via solar cells.
In order not to overload the battery, I will Charge my iMiEv with only about 500W.
How can I do it?
 
Without modifying the car, the slowest it can charge is 720 watts, maybe 660 watts.

How "used" is the battery? It should be able to discharge at least 1,000 watts.
 
The 2012 USA version EVSE can be reprogrammed to use currents as low as 6 amps - With a 100 volt input, this would allow charging at 600 watts

You can build your own EVSE using parts/code from Open EVSE - http://code.google.com/p/open-evse/ but again, I think you're going to be limited to 600 watts *if* you have a 100 volt source. If you're using a European 220/240 inverter, the lowest any EVSE would go is still 6 amps I think and that would be over 1 Kw

A used forklift battery should not mind putting out 1 Kw - I think the secret would be to limit the discharge time so the battery never goes below about 50% SOC and then recharge it again. Wet cells do not like deep discharges, but will give you many, many cycles evn at relatively high discharge rates if you limit the discharges to 50%

If you're still concerned about the battery, I think you could build some sort of switch which would cycle the inverter on for 1 minute, off for 1 minute and then repeat for hours and hours - This would greatly limit the battery heating and the battery would live longer doing this than continuously discharging at 1 to 1.5 Kw

Don
 
Hi Don.
I it's a really good idea.
I will do so:
An electrical relay and a timer that turns on and off, so that consumption is approximately 500 Wh.
Thanks.
 
Don said:
If you're still concerned about the battery, I think you could build some sort of switch which would cycle the inverter on for 1 minute, off for 1 minute and then repeat for hours and hours - This would greatly limit the battery heating and the battery would live longer doing this than continuously discharging at 1 to 1.5 Kw
The car's onboard charger is not manufactured or rated to be repeatedly switched on and off every minute for hours, and doing so will reduce its life or cause it to fail prematurely.
 
I agree with RobertC. Starting and stopping charge like that isn't good on the charger and relays/contactors. Plus, It'll take 40+ hours to charge the car if you don't run the forklift battery flat first. Remember, also, that if you have 500 watts of incoming solar power, you can charge at 1,000 watts and the battery will still only see a 500 watt load.

Forklift batteries are designed to discharge up to 1,400 watts. Your best bet is to have the cord upgraded by the way of EVSEUpgrade (if you're in US or Canada), and set it for 6 amps at 120 volts, which will be around 660 watts (car stays about 1/2 an amp below the EVSE pilot signal).
 
RobertC said:
Don said:
If you're still concerned about the battery, I think you could build some sort of switch which would cycle the inverter on for 1 minute, off for 1 minute and then repeat for hours and hours - This would greatly limit the battery heating and the battery would live longer doing this than continuously discharging at 1 to 1.5 Kw
The car's onboard charger is not manufactured or rated to be repeatedly switched on and off every minute for hours, and doing so will reduce its life or cause it to fail prematurely.
Interesting. Where did you find that bit of info?

Don
 
It is possible to use the DC charging plug?
The voltage from the truck battery is transformed up to 4V x 88 = 352V
and can only provide approximately 1.5A, thus approximately 500w.
 
JKO, none of us have hacked the CHAdeMO inlet yet. It is more feasible to tap into the main DC bus between the battery charger and the battery or between the battery and the inverter. When you say forklift battery, I think of a lead-acid battery that is typically 36-48V and weighs over 2000 lb/ 900 kilo. A battery like that, with 500+ amp-hr (18-24 kWh) capacity should be able to serve a second life discharging continuously for a Level 1 recharge (900 Watt) without any trouble. After all, on a forklift those batteries are called upon to provide on the order of 12 kW for short bursts, and 7 kW continuously.
I have charged on L1 off of a 48V input grid-tied 120V output inverter with no problem. However, if you're connected to the grid, the losses involved in charging and discharging lead are greater than simply inputting solar to the grid and then pulling those electrons back out when you need a charge.
 
One issue with low charge rates is wasted AC kwhr's to charge the same amount of KWH's back into the battery

Why?

Well when you set your EVSE to charge at the the on board chargers full output (3300w) not all of it gets to the battery. A small portion is lost in the inefeciancy of converting AC to DC. Though in % terms a grater portion is wasted powering contactor, coolant pump, ECU, DC to DC converter and a few other things. This adds up to a few hundred watts.

Lets just say the system on loads are 250w. Now if your charging at 3300w you only have 2950w to charge the battery with. If your charging at 1000w you only have 750w to charge with. Given the charger will be on for a lot longer time at 1000w the total kwh's wasted to keep the car on while charging will be significantly more the slower you charge.

For max efficacy or min KWh from the wall plug to recharge your Imiev always charge at 3.3kw.

Kurt
 
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