How is grid charging different than driving?

[jeff652]

If grid charging is 'bad' for our batteries as it is cycling them, how is it different from driving down the street and braking to regen charge the batteries? Isn't that basically cycling them as well, but much more current at once?

I am not an electrical engineer (obviously) so sorry if this seems like a dumb question, but it seems to me that grid charging would be easier on the pack than driving the car due to the low amperage and slow charging rates. I am struggling to understand why people are so cautious about grid charging too often and recommending against it as compared to the advice that frequently driving the car is 'good' for the IMA battery.

For the record I did wire up my fan (wooT) and only grid charge monthly now, just curious about the above.

Thanks!
Jeff

[highwater]

I'll have to look and see just how long I've been grid charging (3-4yr?), but it is an every commute day event.
I do not plug in at work.
Over the course of the daily round trip, the battery will usually be depleted down to 4 bars indicated SOC, and often down to the 3 bar nuance, where it hangs. Hardly ever does a negative drop out. Plug it in over night and go again next day.
Use MIMA to climb hills, and 12v usage burns up the Amphours.

Time will tell I guess.

Randall

[diamondlarry]

Originally Posted by jeff652

If grid charging is 'bad' for our batteries as it is cycling them, how is it different from driving down the street and braking to regen charge the batteries? Isn't that basically cycling them as well, but much more current at once?

I am not an electrical engineer (obviously) so sorry if this seems like a dumb question, but it seems to me that grid charging would be easier on the pack than driving the car due to the low amperage and slow charging rates. I am struggling to understand why people are so cautious about grid charging too often and recommending against it as compared to the advice that frequently driving the car is 'good' for the IMA battery.

For the record I did wire up my fan (wooT) and only grid charge monthly now, just curious about the above.

Thanks!
Jeff

I too have wondered that; 350mA vs. 50-100A while driving. The only thing I can figure is the concern is over charging it to a higher level (100% vs. 80ish%) than what the car's systems allow?

Originally Posted by highwater

I'll have to look and see just how long I've been grid charging (3-4yr?), but it is an every commute day event.
I do not plug in at work.
Over the course of the daily round trip, the battery will usually be depleted down to 4 bars indicated SOC, and often down to the 3 bar nuance, where it hangs. Hardly ever does a negative drop out. Plug it in over night and go again next day.
Use MIMA to climb hills, and 12v usage burns up the Amphours.

Time will tell I guess.

Randall

That's very encouraging on the 3-4 years without negative drop outs as I employ a similar routine (plug in nightly) with the exception that I don't deplete the pack down to those levels.

[E27006]

Three reasons,

1)
grid charging = slow high-quality charge of a fraction of an amp over several hours, cells charge to full with little stress.

Regen charging is fast aggressive low-quality charge, 30 amps on braking, or upto 10 amps during hidden background charging or even more during a forced charge when pack is low and 4 bars show on charge gauge. Cells sometimes may inaccurately measured/detected as "full" by BCM leading to imbalance and negative recals etc.

2)
Weak or aged packs respond better to grid charging compared to regen charging, prolonging life and use of the pack and delaying outlay for replacement.

3)
benefit of increased mpg, cost of mains power is low ( pennies ) and keeping the pack topped up by grid charging means the car does less hidden background charging during the drive ,background charging is an extra load which burns expensive fuel.


Note:
Hidden background charging occurs when the SofC of the pack is about 50%, IMA charges pack at anything up to 10 amps for several minutes at a stretch, the IMA gauge will not show this charging event, but you may notice a sluggish response of the car.

You can truly observe the hidden charging if you have an OBD11 gauge on your car.

[diamondlarry]

Originally Posted by E27006

Three reasons,

1)
grid charging = slow high-quality charge of a fraction of an amp over several hours, cells charge to full with little stress.

Regen charging is fast aggressive low-quality charge, 30 amps on braking, or upto 10 amps during hidden background charging. Cells sometimes may inaccurately measured/detected as "full" by BCM leading to imbalance and negative recals etc.

2)
Weak or aged packs respond better to grid charging compared to regen charging, prolonging life and use of the pack and delaying outlay for replacement.

3)
benefit of increased mpg, cost of mains power is low ( pennies ) and keeping the pack topped up by grid charging means the car does less hidden background charging during the drive ,background charging is an extra load which burns expensive fuel.


Note:
Hidden background charging occurs when the SofC of the pack is about 50%, IMA charges pack at anything up to 10 amps for several minutes at a stretch, the IMA gauge will not show this charging event, but you may notice a sluggish response of the car.

You can truly observe the hidden charging if you have an OBD11 gauge on your car.

I have seen the negative impact on FE at anything under 19 bars on the SoC gauge. If all goes well, by the end of the day today or tomorrow, I'll have an OBDII C&C gauge in my car to keep better tabs on this.

[Willie Williford]

dl;
I notice you also have a CARD switch (Calpod).
I've noticed via the OBDCC gauge a .1-.4 amp charge going into the IMA battery most of the time with the switch ON. Of course I have a deterioated pack, so I accept that.

You will find the OBDCC gauge very helpful.
HTH
Willie

[Eli]

It's not a whole lot different if the pack is balanced, other than being able to charge the pack to 100% charge.

Where it becomes critical is when the pack isn't balanced.

You can have cells that are both nearly empty and nearly full. The car by itself is incapable of dealing with this.

When you use assist, the cells that are nearly empty become depleted quickly. The systems see this, and a negative recalibration is performed.

When you begin charging again, the cells that were nearly full become full quickly since not much charge was used before the last negative recalibration. This causes a positive recalibration.

The cells that were empty are still nearly empty. And down and down the pack spirals.. when this window gets small enough, an IMA light is thrown.

The only way to overcome this is with grid charging. This will let you charge all cells to 100% full. The pack is still deteriorated, as something caused it to become out of balance in the first place, but it's better than nothing.

Edit: I guess I should have read the OP rather than just the title of the thread.

The reason for the recommendation not to grid charge too much is because it's an unknown, so we're being conservative... the thought being that it would be better to grid charge not enough and work up rather than to start out with too much and work down.

Continuously trickle charging a NiMH cell isn't good for it, but it's an acceptable risk in order to help balance out the pack. I don't imagine there's anything wrong with grid charging every week or even every day, but it shouldn't be a long 12-18 hour soak charge.

[highwater]

I looked it up in my logbook.
Grid charger installed between May 2nd and May 11th 2008.
Approaching 4 years.
Mileage was 100K plus 95. Currently at 147K.

Randall

[Cobb]

Basically the hybrid repair guy says having a pack with a bad cell, that bad cells prevents the depth of discharge or recharge from going that high. So lets say a balanced pack is used 80% of its capacity, if it had a bad cell its only used down to 10% before you get an IMA error.

The least you cycle from empty to full the more cycles you got and most cells have a limited number of cycles.


Sent from my Autoguide iPod touch app

[thedhgroup]

Originally Posted by Eli

Continuously trickle charging a NiMH cell isn't good for it, but it's an acceptable risk in order to help balance out the pack. I don't imagine there's anything wrong with grid charging every week or even every day, but it shouldn't be a long 12-18 hour soak charge.

What exactly "is not good"? Is it the possible heat? Do the cells swell and or let off gas or something or is it a chemical reaction thing? If it is a heat thing, what would happen if we used 100ma instead of 350ma? I know it would take forever but...

Here is my plan. Currently I charge at 750ma (twice a day when over 40 degrees F.) but I have a timer that shuts it off after 3 hours. Seems to trigger a positive recal quite nicely. Sometimes 3 hours is not quick enough for me. Sometimes I only stop for an hour. I'd like to build a 2amp charger that runs up to 1.5 hours, replace the stock fan with something that actually moves air and then a 100ma charger would run indefinitely if bat temps are at or below 90 degrees. (anybody else wanting to do the same thing should take heed from the experts, I'm not one, I generally just push buttons until I get something to work)

Heck, I brought my pack back from near dead so I don't care if I fry it. I have a new one waiting to take its place. Today I was feeling frisky so I did lots of full assist runs, killed my MPG but the pack held up down to 3 bars without a neg recal. I've been charging twice a day for 6 months if over 40 degrees. Under 40 degrees I don't get a positive recal so I gave up trying.