charging question

Basically, the question is: Is it more efficient (i.e. less expensive) to charge at 120 Volts or 220Volts?

Mitsubishi literature implies that at 120v, it takes about 22 hours for full charge. At 220V, it takes more like 7 hours, which is only one third as much. Stands to reason that at 220v, with two hot leads, the charge should take half as long.

Why is it actually only one third as long? Does the 220v charger work at a higher amperage? Or does the battery chemistry just charge better at higher voltage?

The charging current is higher at 240v than it is at 120v. According to the manual page 9-7, 240v has 15A max and at 120v it is 8A max. I note that the power seems a little less for the 240v rate than the 120v rate using V x I. (3.3kW vs 1.0kW) Maybe it is less efficient to charge at higher current rates.

I have a Silver Miev ES and have put 700 miles on it using only the level 1 charger. I seem to get about 1 bar added for each hour of charging. My Brand Electronics meter reports it is charging at about 970 watts.

SteveB said:

The charging current is higher at 240v than it is at 120v. According to the manual page 9-7, 240v has 15A max and at 120v it is 8A max. I note that the power seems a little less for the 240v rate than the 120v rate using V x I. (3.3kW vs 1.0kW) Maybe it is less efficient to charge at higher current rates....

.

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Yeah, if this is true, that would mean that 220Volt charging is less efficient

I can add:
I charge at home off 120v with an SPX EL50600 EVSE because it will work with 120v or 240v and it and the current is adjustable. It draws 14amps at 120v. I started trying to track my power usage with a kill-a-watt meter and it seemed to take about 20kwh to fill the 16kwh battery. Then at work I charged at 1/2 battery level and the charge point EVSE read that I used 8kwh of energy and it was WAY faster. My experiences seem to indicate that 220v is more efficient, but its not very scientific.

The question on the table is whether it is more efficient to charge using 120vac or 240vac.

The diode voltage drop in the charger in the car that rectifies the input voltage is, percentage wise, higher at 120v than 240v and thus charging at 240v is probably very slightly more efficient. The answer is that, for all intents and purposes, it doesn't matter. I certainly wouldn't worry about it.

The charger, if left alone, will fully charge the battery pack and will stuff the same amount of energy into the battery (in kWh), irrespective of the input voltage.

The other points brought up are charging rates (which has nothing to do with charging efficiency).

The charger takes the input ac voltage and converts it into the appropriate very carefully regulated and managed dc voltage/current to charge the battery - it feeds the proper voltage/current level irrespective of the input ac voltage. Putting 240vac into the charger does not translate into the battery seeing a proportionately higher applied voltage. What we do have limiting us is the amount of current the EVSE will allow the car's charger to draw or the maximum that the car's charger itself can draw. In the case of the Mitsubishi Level 1 EVSE it is 8A at 120VAC. At 240vac, the iMiEV onboard charger draws a maximum of somewhere under 13A, which can be decreased by the Level 2 EVSE.

Depending on the actual input voltage (and probably temperature), I've measured the rate of charge at 120vac to be around 960W using the Mitsubishi (Panasonic) Level 1 EVSE, and at 240vac it's around 3.06kW using my SPX Level 2 EVSE with no current limiting. At the ChargePoint station I've seen 2.86kW, and I don't know what the limiting factors are but I suspect the input voltage may have been down to around 220vac for the ChargePoint.

For myself at home, I simply use the rough number of 3/4bar/hour at 120vac and a little under 3bars/hr at 240vac so as to set my remote timer to bring the car up to about 14bars and not fully charge. The only time I fully charge my iMiEV is when I know I'll be taking a long trip, and I do that just before leaving.

Finally, being old school, I prefer to charge my battery pack slowly to minimize internal heating due to the chemical reaction and thus, if I have the time, I use the Mitsu 120vac 8A charger. My 240vac is used daily for quick top-ups in-between errands. The current going into the batteries is so low using either 120vac or 240vac (compared to the currents when driving) that I'm pretty sure it doesn't matter which you use ... hey, it's built to take the CHAdeMO input which stuffs well over 100A dc into the pack.

HTH

When i get my blink charger hooked up in the next week or so i will be able to tell you how many kW i used in a week vs miles or how many kW per bar for a charge.

I will let you guys know that i don't drive the car light or in the city much most of my driving is 55mph and then back to zero for stop signs so my kW per mile might not look too good but it is still way cheaper then driving the diesel to work.

Just a wild guess:

The i-MiEV charger built in does not use transformers (the high amperes part at least) and it is designed to run on 120V and 240V without a change. So the circuit rectifying the incomming AC is a voltage doubler with two diodes for 120V on terminals L1 and N. That same circuit doubled for L2 and N becomes a bridge rectifier when 240V are connected between L1 and L2. The BMU is driven from the rectified 240 AC. It works the same for 120 AC and 240 AC resulting in the same efficiency. Current sensors limit the strain for the diodes to 8A so for 120V L1 only, the diodes take 16A but after voltage doubling (Each diode feeds a capacitor. The capacitors are switched in series resulting in 240V DC.) only 8A are present on the internal 240V DC. Twice the same circuit results in 16A for 240V using both L1 and L2. That is why 22 hours for 110V AC and 11 hours for 240V. But my i-MiEV needs only 7 hours (16A) to charge here in germany. The 10A version of the EVSE needs 9 hours. How come the 22 hours?

Even wilder guess:

60 Hz 120V AC results in the DC swinging at 60 Hz not giving you the full power all the time. 50 Hz 240V AC results in the DC swinging at 100 Hz giving you a smaller gap. If the gaps in the mains power AC sine wave are the culprit for the 22 versus 7 hours needed for charging - how about DC charging?

With an internal 12V battery in the i-MiEV there is no need for transformers. Nothing but 240 DC needed for charging. Solar energy is DC not AC and inverters do waste energy. Putting solar arrays in series to get two columns of 120V DC each (20 car batteries results in 240V DC). +120V DC fed to L1, -120V DC fed to L2 and N fed to zero might do the trick.

Please dont try this at home. The EVSE needs AC because it has a builtin 12V DC supply that is using transformers. Transformers fed with DC with blow either the fuse or themselves.

I'd like to hear from somebody who knows the charger internals if it it works and if it could be recommended.

I know from a modified CHAdeMO charger that was solar powered in this way.

peterdambier said:

Just a wild guess:

The i-MiEV charger built in does not use transformers (the high amperes part at least) and it is designed to run on 120V and 240V without a change.

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No question there's not a main power transformer in the charger - A 3.3 Kw transformer would weigh more than the entire charger, plus it would limit the input voltage to fixed numbers as you say. Without a transformer, the input voltage can be anything from 90 volts to 250 volts and any voltage in between. The same charger works on 100 volts in Japan, on 120 or 240 in North America and on either 220 or 240 in most of the rest of the world. It would work just fine on 175 volts too, if that's what you plugged it into. The input must be 50/60Hz AC though - You cannot put any DC voltage in the L1/L2 power socket

Even wilder guess:

60 Hz 120V AC results in the DC swinging at 60 Hz not giving you the full power all the time. 50 Hz 240V AC results in the DC swinging at 100 Hz giving you a smaller gap. If the gaps in the mains power AC sine wave are the culprit for the 22 versus 7 hours needed for charging

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No - The difference in recharge times are solely the result of the EVSE limiting the number of amps the charger is allowed to draw from the wall - If the EVSE allows 120 volts @ 15 amps, the L1 recharge time will be twice that of an L2 EVSE set to 15 amps @ 240 volts. Full wave rectification allows for 100% full power DC output voltage all of the time, irregardless of the input frequency . . . . no 'swinging time' - No difference when used on either 50 or 60 Hz

The really unique feature of the charger (at least to me) is that it will limit the amount of current it draws from the wall plug to any number the EVSE you're using tells it not to exceed. If you use the supplied OEM EVSE, it only draws 8 amps from the outlet, but if your EVSE tells the charger that it can use 10, 12 or even 15 amps at 120 volts, the charger will set itself to those numbers too - Same for 240 volt operation on L2 - If the EVSE tells it to use 6, 8, 10, 12 or 14 amps, it will limit itself to whatever number the EVSE tells it not to exceed. This is what makes it safe to recharge the car in any garage, anywhere in the world. So long as it's used in conjunction with the proper EVSE, it will never blow a fuse. Pretty neat!

As to how the EVSE/charger relationship works, you can study up on the SAE J1772 Protocol, which is the standard that all EVSE's must adhere to. This is why you can plug an iMiEV, a Leaf, a Volt, a PHP (Prius) or most any other EV into most any EVSE plug around town and get a charge - The EVSE and the car's onboard charger 'speak' to each other

http://en.wikipedia.org/wiki/SAE_J1772

Don

Some cars, and some EVSEs, adhere to the J1772 standards differently than others.

For example, some EVSEs do not do the "diode" safety check.

Thank you for all suggestions.

We have been in the wild this weekend, joining a pirates party convention. Charging in the wild from CEE 400V/16A, CEE 400V/32A. We did not succeed to charge from CEE 230V/16 because 8 caravans shared 4 sockets - no dice. Finally we even had to use one of the new power columns with RFID and Menekes Plug. We were lucky to plug in as a motorcycle with the infamous local Schuko Plug (pronounced shuko plug) using the hotels RFID card.

Talking to a lot of people we agreed not to mess with the J1772. What might work for one car might create havoc for another car of the same manufacturer. J1772 is not meant for DC but CHAdeMO is. CHAdeMO chargers are not that expensive (the e8energy at least) compared to the money spent by our cities for constructing roundabouts

430 kilometers driven, seen the turtle 3 times. We crept home finally dropping one charging point and still did not wake the turtle. Maybe she felt cold?

In case you wonder i-MiEV how to charge from 400V/16A ? It is 3 phase mains. We used one phase only and that is 230V/16A. But an i-MiEV with a big red plug looks amazing to non techs

Has anyone given any thought to dc charging the imiev from a small solar array directly ?

I believe the OEM evse would not work without mods because of the ac transformer it uses to generate low voltages for the internal circuit. But other then that would the onboard charger work off of dc ? Lets say five 250 watt panels would be about 140 volts at about 6.5 amps. Plenty for a nice summer day charge and no inverter very cost effective.

I suppose the best way would be to get enough solar to charge the pack thru the chademo port. Then you avoid the charger loss. But that would take about 14 panels and supply about 2.5 kw the car would easily charge completely in less then a summer day.


Any thoughts ?

Don.....

DonDakin said:

Has anyone given any thought to dc charging the imiev from a small solar array directly ?...I suppose the best way would be to get enough solar to charge the pack thru the chademo port. Then you avoid the charger loss. But that would take about 14 panels and supply about 2.5 kw the car would easily charge completely in less then a summer day...

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Don, a crude (and very inefficient) ac way is to have solar feed a battery charger/regulator to feed a 12v (for example) battery to feed an inverter to feed our EVSEUpgraded EVSE set to a reduced-current setting.

CHAdeMO on the i-MiEV has a problem: unlike the Leaf, there is a minimum current limit of about 5A, below which our CHAdeMO cuts out. Pity.

has any one successfully charge the iMiev using the stock charger powered by the Secure Power outlet from the solar Sunny Box Inverter ? these inverters have a 120vac, 2kw, outlet energized when the grid is down:

http://www.sma-america.com/products/solarinverters/sunny-boy-30-us-38-us-50-us-60-us-70-us-77-us.html

I haven't read the inverter manual carefully yet; but I think it automatic restarts if a cloud passed by, given sufficient sun shine afterward.

Thanks