LV2 Charging question from a newbie

Hi all,
Just got my new 14 I-Miev last week and I had my first Level 2 charge last night. I want the battery to last as long as possible. I've read other threads in this forum warning against stressing out the battery (ie avoid turtle mode etc).

I had 5 bars left when I charged last night. My questions are: (1) When should I start charging the battery? (2) Is there any difference if I charge it with for example 9 bars left vs 2 bars left?

Thx

kitkit said:

I had 5 bars left when I charged last night. My questions are: (1) When should I start charging the battery? (2) Is there any difference if I charge it with for example 9 bars left vs 2 bars left?

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Your starting to recharge at five bars was fine, and just about the way I do it myself. Unlike lead acid (which should always be kept fully charged), lithium is happiest at around 50% state-of-charge. About the worst thing you could do for your battery pack is to fully fully charge it and then leave it sitting unused in the hot sun. You can estimate your L2 charging as being about three bars per hour of charge, and you can set your normal charging regimen by using your Remote to set the car to turn off before it gets to the top. I try to keep my battery pack between four and thirteen bars, only fully charging just before taking off on a longer trip. In your very mild climate I don't think it'll matter much, anyway.

Congrats.

(And since Joe beat me again)Regarding maximum battery life, the following guidelines will go a long way to making our batteries last.

1. Avoid sitting at a full charge when possible, especially at higher temperatures (80 F and above).
2. Try to keep the battery above freezing during the winter. For this, CaniOn or OVMS (Open Vehicle Monitoring System) makes temperature monitoring possible.
3. Try to minimize full throttle.
4. When storing the car or leaving it sit for extended periods, store it with 4-7 bars on the charge gauge and do NOT leave it plugged in. I heard one member in a hot climate left it plugged in and sitting at full for two weeks and had to have the battery replaced. When the i-MiEV is off, it's off. There is no energy flow in or out of the pack, and the pack itself has a very low self-discharge rate.

For number one, I always let the car fully charge, and it does sit for approximately 2 hours at full charge before I leave. I haven't noticed any degradation yet. The timeframe I have in mind is more than 12 hours to avoid sitting at full. So, to answer your question about charging, level 2 charges at roughly 3 bars per hour. Max charge time is 5.5 hours. Level 1 is roughly one bar per hour with a max time of 14 hours.

For number two, I use a slow charging rate to help keep the battery warm. This would be 120 volt charging, at either 8 or 12 amps. If the pack is below freezing, use the slowest rate possible, and if you have somewhere warm to park the car for a while, let the car warm up before charging.

Number 3, I'm guilty of breaking. Probably not that harmful to the pack anyway, but helps extends range. You do want to avoid it at low charge, though.

Number 4, the longest I've left my car was a week, and I kept it at around 7 bars. Still had the same number of bars when returning.

This may sound like a lot, but they are simple things. The fun thing is, you can follow the same guidelines for your cell phone or laptop and make those batteries live longer. I know Dell machines (at least Latitude and Precision models) have the ability to set the maximum charge level. There is no difference in battery life starting charge at 9 bars vs. 2. The i-MiEV will simply charge in less time at 9 bars. I'd probably charge every night (assuming that's the difference between 2 and 9 bars). That way if there is an emergency or the car didn't charge for some reason, you still have more than half a charge available.

The i-MiEV battery pack should live quite a long life. They have a much easier life (and are a more durable chemistry) than any battery found in consumer electronics.

kitkit said:

My questions are: (1) When should I start charging the battery? (2) Is there any difference if I charge it with for example 9 bars left vs 2 bars left?

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As others have already pointed out, Lithiums are happiest if kept between about 20% and 80% SOC. We try to charge based primarily on how we'll be using the car. As a general rule, we try to keep it between about 3 and 13 bars. We never fully recharge unless we're about to take a trip requiring the full range of the car and that doesn't happen very often. We also never plug it in if it's still got more than half a charge - Usually it doesn't get plugged in until we're down to 3 to 5 bars

Our regular commutes are on the order of 10 to 40 miles, so leaving it partially charged (rather than fully charging it) means that even if it's half full, we can still do 90% of what we need - If we need to go a little further, we charge it a little more just before we leave

If it hasn't had a full recharge in 5 or 6 weeks, we'll plug it in L1 and let it fully recharge overnight, just to give the BMS a chance to evaluate the battery. I think Mitsu recommends this every month or so

The car was designed to be as 'idiot proof' as possible and they were also trying to emulate a 'normal' car as much as possible, so fully recharging it every day, no matter how empty or full it is when you start the recharge shouldn't hurt it much, but they do caution against recharging when it's nearly full - Those of us who are more careful and try not to keep it full as much as possible are just *hoping* this protocol will get us an additional 15% or 20% of life from the battery that 'ordinary' users won't see. Whether this actually gains us anything won't be known for several more years ;-)

Don

Don said:

Those of us who are more careful and try not to keep it full as much as possible are just *hoping* this protocol will get us an additional 15% or 20% of life from the battery that 'ordinary' users won't see. Whether this actually gains us anything won't be known for several more years ;-)

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Very well phrased, Don. My wife and I recently needed to take a houseful of guests up to SFO - a 35-mile trip one way, so we went with our two i-MiEVs in tandem. Mine (bought used) has a brand-new battery and our original (babied) has over 3 years and 38,000 miles (61,000km) on it. Identical number of bars consumed by each of the two cars during this trip. Encouraging.

Don said:

If it hasn't had a full recharge in 5 or 6 weeks, we'll plug it in L1 and let it fully recharge overnight, just to give the BMS a chance to evaluate the battery. I think Mitsu recommends this every month or so

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Thanks for all the tips everyone! This site is very resourceful.

I have another question regarding battery evaluation. I remember reading somewhere on this forum that Mitsubishi recommends charging the battery with 2 bars left once in 6 months? Do I have to use the Mitsu LV1 charger? Or I can just use a LV2 charger?

Level 2 will work just fine for the calibration charge.

What happens if you run battery down to 2 bars and then refill on a regular basis ?

I plan on driving till it is pretty low then charging over night full.
My commute is only 16 miles total per day, on all back roads.
I am hoping to only have to charge once, maybe twice, a week.

So if I did this, would it keep the batteries better Calibrated ??

tigger19687 said:

What happens if you run battery down to 2 bars and then refill on a regular basis?

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As a general rule, Lithiums like to sit at around the 50% SoC. The more you deviate from this, either way, the less happy they are. Your daily commute should only consume three or four bars/day. If it was me, unless it's a great inconvenience, I would simply charge up to about 10-11 bars and then recharge again when it gets down to 5-6 bars, or maybe keep it a bit higher on a daily basis to accommodate the unexpected excursion? We rarely ever get down to two bars. We're really picking nits here.

tigger19687 said:

So if I did this, would it keep the batteries better Calibrated ??

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Calibration of the SoC and cell balancing are two different parameters. Cells get top balanced every time you fully fully charge the car, the last hour of charging usually spent balancing (gently topping-up each cell) as the current into the pack decays. Sufficient if this is done maybe once every few months (this is where CaniOn shines), and there is some evidence suggesting that one doesn't want to often put the cells at that high a voltage unless the car is driven immediately afterwards (sorry, can't find the link to support that comment). Anecdotally, I have a Lithium(NMC) pack in one of my Sparrows that hasn't been balanced in 1-1/2 years, and with all but one of its 72 cells within just a few millivolts of each other.

As best we can tell, state-of-charge calibration assessment takes place when the pack gets recharged fully after starting out at a low state of charge (two bars or below). According to a letter Mitsubishi sent out, this only needs to be done once every couple of years.
Ref: http://myimiev.com/forum/viewtopic.php?p=1031#p1031