Battery charging

[Arturo]

Has anyone developed a way to charge the battery bank so when you take off there fully charged? Solar panels would need the voltage jumped to be able to charge the battery. Anyhow, we have a lot of talent in this forum so I just wanted to ask. Arturo

[Insightful Trekker]

No, not yet. When are you planning to start.

See:

How insane/unlikely would it be to ad pv cells?
http://www.insightcentral.net/forum/vie ... php?t=5198

HTH!

[b1shmu63]

The topic has under various headings been discussed at length. Although it would undoubtedly have some effect on your lifetime mileage, it would in my opinion be one of the less effective mods to achieve this. It would also decrease the life of the batteries even if done correctly (see additional post below). As such it would likely void your IMA warranty. Doing it correctly would be very costly in terms of time, effort, and materials. Doing it incorrectly could seriously damage you or the Insight.

An energy related mod that would likely save more fuel would be installing a block heater to preheat the engine in winter when mileage is at its worst.

Charging the 12 volt battery with solar or AC is also a productive project as it can cost less than 20 dollars. Having a warmer / charged 12 volt battery on a cold day will decrease the load on the IMA system, indirectly supporting the charge maintenance.

[b1shmu63]

If IMA charging over night was done properly the charge should never exceed 80 percent as per Honda's design. This would not decrease battery life significantly. However, assuming that this mod is to achieve some useable amount of mileage increase, the battery would have to be depleted in the course of a day’s driving before charging in order to achieve even a small difference. This daily cycling of the battery would have an effect on longevity. If this reduced battery life by 20 percent, it would, for example, reduce the life of the battery from 10 years to 8 years. Not only would this represent an inconvenience but it would also effectively cost one fifth the installed replacement cost. Assuming an installed cost of 2500 dollars this cost is five hundred dollars or 62 dollars a year. At $2.70 per gallon that is 23 gallons of gas. An Insight driven 20,000 miles per year at 65 MPG uses 308 gallons. Mileage would therefore have to rise 7.5 percent to 70 MPG. It is doubtful that the small amount of energy in the battery could achieve this. Therefore even if electrical power were free and the mod was free, it still would not likely make economic sense at today’s gasoline and battery costs.

[Arturo]

It doesn't make sense if it shortens the battery life. Why does honda only go 80% on the charge? Most batterys last long by just using the upper 50% of charge. Just thought someone would have tried adding a solar panel to assist while driving so you don't end up in situations where you are charging while going uphill. Ive seen Mike 's setup on his insight.I'm going to do his setup in the future . Arturo

[b1shmu63]

It doesn't make sense if it shortens the battery life.

Agreed. Charging the IMA battery does not make economic sense if it shortens battery life.

Why does Honda only go 80% on the charge?

The IMA system charges between 20 and 80 percent. In this range the battery internal resistance is low increasing throughput efficiency and minimizing out gassing or the chance of cell reversal in series connections.

Most batteries last long by just using the upper 50% of charge.

In a lead acid system resistance goes up as the electrolyte PH goes to neutral. Deep discharge is particularly hard on lead acid batteries. NmH batteries are best used in the above 20-80 % range.

Just thought someone would have tried adding a solar panel to assist while driving so you don't end up in situations where you are charging while going uphill.

The IMA battery system nominally puts out 14,400 watts max. Mikes solar panel puts out 150 watts max. Unless the energy is stored, it won’t give much assist on hills.

I’ve seen Mike 's setup on his insight. I'm going to do his setup in the future . Arturo

Presumably you are referring to Mike's impressive plug in hybrid system using lead acid batteries and switching converter modules. However, If you are considering mounting a large solar panel, first watch the Mythbusters myths revisited issue where he tries to hold onto a sheet of plywood in the back of a moving truck.

[Mike Dabrowski 2000]

Nice explanation Kip,
If I may add a few more points.
If you look at the specs on the Panasonic 6.5AH "D" cell NIMH that the insight pack is based on, you will see that they are only specified for 500 charge discharge cycles. That would not get most of us through a year of use. The battery makers found that most of the life reduction with the cells comes when they are under the 20% SOC or over the 80% SOC. When restrained within that range, tens of thousands of cycles are possible. Presently only NIMH has the durability to last the 10-20 year life of the car.
The problem with the 20-80% SOC range is that the voltage stays pretty flat within that range, so SOC determination is difficult and must involve counting the amps used and amps returned, as well as adding temperature and rate of charge /discharge compensations. According to Honda the recalibrations that many people have are due to inaccuracies creeping into this formula, where the car looses track of where the batteries SOC is, so to be safe, when the software is unsure, they recharge to some point to recover. I still don’t totally buy that one, but until we have a better theory we are stuck with it. How do they know when to stop if they don’t know where the SOC is?
When fully charged, there is an easy to see rise then dip in voltage that happens at the 100% SOC point. If each recal is followed by a 100% charge, many of the people with frequent recals would have exceeded the 500 cycles.
Charge the batteries up without the car being turned on,(solar) and you take a real risk of overcharging the batteries, and shortening their life, as well as further confusing the SOC determining system.
As far as recharging on the fly with a solar panel, while it would work, the 150 -possibily 250W that one could fit on the upper surface of the tiny car would be a drop in the bucket. When My booster pack is turned on, I am feeding nearly 2800W into the battery, and I still have to be careful with assist or I will deplete the batteries. Of course I am applying aggressive assist at 100-125 MPG, to keep the MPG over 100, even climbing hills, so the electric is doing much of the work. After using my 2800W for some time, I feel that 4000-5000 watts from the booster system would be perfect. At that rate, I could nearly run off the boost, with the NIMH HV pack only acting as a buffer.
On the AGM batteries I was advised to not let the batteries get below 50% SOC and to always recharge immediately after use to 100%
All part of the care and feeding of batteries.

[Lee]

Mike, a few comment of the workings of the SOC control map or algorithm.

The SOC is determined by an integration function. As such any error in the calculation will throw off the subsequent calculation. A few small errors can add up over time to a large error. As I understand it, the problem comes in if the battery dose not get to the low or high trip indication. As the SOC wander around it can not really tell where it is until it hits the change in voltage that happens at the above 80% or below 20% full levels. The normal usage range of a NiMH battery has little voltage change (you have said this before) but the ends of the range have measurable changes in voltage. So the problem occurs when the SOC has been wandering around in the middle of the charge level for some time and then it runs in to a high or low voltage indication. Then a forced charge is initiated to find the high voltage limit and the SOC algorithm is reset.

Further complicating this is the battery controllers effort to reduce the memory effect of the battery. If the battery is used only in a narrow band (which it must be to extend the life of the battery) the battery will develop a memory and the usable band of the battery will be reduced. This makes it easier for the SOC algorithm to trip on a high or low voltage indicating the limits of the usable range. When this happens the algorithm tries to reduce the usable charge range to reflect the memory of the battery. The SOC algorithm tries to vary the limits of the usable range of charge to reduce the memory effect. Also when it has determined that the memory effect has reduced usable capacity too much it will fully charge the battery to erase the memory. If this happens too many times there is a risk of a cell in the battery dieing prematurely.

As an interesting side note, I can not always say what I think so I try to find public information to back it up. Because of the intense rivalry with Toyota every idea that went in to the development of the IMA system is patented. All patents are public information and searchable on the web, for free. Go to http://www.uspto.gov. look for the patent search page, click on quick search and patent number. 6204636 is the most relevant to this discussion . This will show you the text of the document, if you load there image viewer you can see the pretty pictures. Be forewarned, they do not write these things in English, it’s all in leaglease.

[b1shmu63]

Nice find, I'll have to read it insightfully when I have a bit more time. I think the take home message is; don't mess around with charging the IMA without the battery management circuitry.

[Mike Dabrowski 2000]

Lee
Nice find.
I have been using this SOC determination explanation:
http://www.99mpg.com/Data/downloads/rel ... nation.jpg
which as I understand it came from a technicial training class put on by Honda.
It pretty much agrees with your discription,but has no mention of memory effect, which many people incorectly felt was not an issue with NIMH.
With all of the problems with recalabrations that the insights have had, I sort of doubt that the patented memory effect compensation was included, and since the recals seem to repeat for many people whenever the SOC drops to some repeatable point, the compensation for aging is not working.
It is possible that Honda did not impliment the full algorythm on the insight, but may have on the Civic and later hybrids?
My own experience with 105K on the batteries, the last 25K, with daily 100A assist,and 50A regen, several cycles a day, and never a recal. others that use the batteries sparingly get recals frequently?
My daily usage will cycle the pack fully, light use would tend to keep the batteries near full SOC, and only use a small part of the usable range of SOC, which could induce a memory.
An interesting aside reguarding this. I was given a fluke 196C scopemeter to evaluate. It runs on NIMH batteries. I was studing the manual, and found that it had a battery restore feature that they recomend using 4 times a year where it automatically completely discharges the battery, then completely recharges it to avoid the memory effect.