grid charger/balancer

[aisbell]

Originally Posted by aisbell

I forgot to mention that when I inserted my power meter into the charger circuit at the start of my rebalancing session, the input current measured 0.81 amps. After charging for about 4 hours, the input current had dropped to 0.49 amps. Can those measurements be used to estimate the output current? If so, maybe this would be a way that I could monitor the state of the battery rebalancing.

I bypassed the timer in the engine block heater outlet so that the outlet is powered whenever its circuit breaker switch is on. My Insight had been parked for over a week, so I decided to run the charger/balancer for an uninterrupted 24 hours prior to embarking on a ~200 km test drive in preparation for a week's tour through southern Sweden next week.

Similar to my first charging session, the initial input current was 0.79 amps. After 23 hours of charging, the input current was considerably higher at 0.69 amps than it had been after only 4 hours of my initial charging session. The input current when the output is disconnected remains at about 0.16 amps.

I am surprised that the input current remained so constant over 23 hours and that this behavior differed from my first charging session. I would think that as the battery voltage increases, the input current would decrease more. This makes me yearn more for an output current meter or indicator of some kind. I feel like I'm shooting in the dark. Peter, have you had an opportunity yet to research an LED output current indicator?

[Mike Dabrowski 2000]

Art,
The initial HV battery SOC when you start the charging will determine the current drawn from the grid, and should be a rough indicator of output current, but you really need an ammeter and voltmeter on the output circuit to know what is happening with any degree of certainty.
If you open Peters grid charger box, and run it with the cover open, you will be able to put a voltmeter across the big power resistor. This voltage will depend on the output current going to the pack, and will act like a current shunt. Once we know what the minimum and maximum voltage that is across the resistor when the pack is empty or full, a simple led and additional resistor would allow you to see the led brightness change as the current changes during charging. Instead of an led, an analog or digital voltmeter and series resistor would allow direct reading of output current.
Based on Peters initial test, and the resistors 33ohm value, it looks like a 1000 ohm resistor and a 20 mA led across the power resistor should work nicely as a current indicator, just make sure that the LED polarity is correct.

On my grid charger with the constant current supply, I was able to simply put a 350ma 1W led in series with the charger output. When the charger is at its cc , the led lights up fully, and as the max voltage is reached (adjustable), the current rapidly drops off, and you can see the led brightness also drop to show that you have reached the full charge point.
http://www.99mpg.com/projectcars/mim..._display.jpg,0

[retepsnikrep]

I'm still fiddling about no updates yet.

Art was the battery better after the grid charging.

I may yet go for a 350ma cc design for the final version! Alla MD

[crx_rogus]

Originally Posted by aisbell

This makes me yearn more for an output current meter or indicator of some kind. I feel like I'm shooting in the dark.

That's why I use a Kill-A-Watt to measure watt-hours in from the grid, to give a rough idea that of course has to be trimmed down some to account for waste, and does not measure straightforward volts x amps into the actual battery pack (hours, watt-hours, watts, volt-amps relating to power in, yes).

Roger

[retepsnikrep]

I've been making some changes to my grid chargers and they now uses 3 x 48v psu's adjusted to 42V and one of Mike's 0-48v 350ma Constant Current power supplies. This gives a 174v maximum output. Testing one today seemed to work very nicely. I'm experimenting with adding a simple zener/resistor/led across the CC power supply output which turns on the led when it's output voltage reaches 40V or so meaning the actual charger voltage has reached around 166v. The NIMH packs seem to stabilise at around 164-167v so this would give a good indication that it has reached around the right voltage. I'm using a pack on the bench for this final tweaking to also take into account the two diodes in the charging leads etc. Once I have a reliable zener/resistor/led value I'll post details and final pics.

If this zener switch/led proves accurate enough it could control a fet/transistor in the output lead turning the charger output off when the target voltage is reached. Once the fet turns off the CC charger would not be under any load and it's voltage would rise further, turning the zener circuit on harder so the fet could not turn back on again. Have to see.

[aisbell]

Originally Posted by retepsnikrep

Art was the battery better after the grid charging.

My battery has behaved normally after not being used for 6 months while in Sweden last winter and after another 2 months of no use while my Insight was being shipped to Sweden. I am concerned that any imbalance that developed during those periods of non-use will eventually cause problems like I had with my first 2 batteries, so I'm using your grid charger to try to minimize any imbalance.

So I am unable to determine whether my battery's condition has been improved by the grid charging. I certainly hope that charging my battery to a higher state of charge than Honda intended is doing more good than harm.

I will be parking my Insight in an unheated carport in about 2 weeks for another 6 months. At least the battery temperature will be considerably lower than it was when my Insight was parked in Honolulu. I have read that self-discharge is slower at lower temperatures, so maybe the resulting imbalance will be less. But when I return, I'll be able to fully charge it using your grid charger before I drive my Insight anywhere, so hopefully that will help in the long run.

[retepsnikrep]

Art

I'm sure the charger is doing some good. Yours is a good test vehicle with such a long period of inactivity. The cooler temp is better for lower self discharge. Do you have an Insight for use in Hawaii as well?

I'm sure you are doing this already but I would disconnect the 12v battery or even remove it during storage and switch off the nimh pack at the back. This also makes possible theft of your vehicle more difficult if you take out the 12v battery.

Peter

[crx_rogus]

Originally Posted by retepsnikrep

I've been making some changes to my grid chargers and they now uses 3 x 48v psu's adjusted to 42V and one of Mike's 0-48v 350ma Constant Current power supplies. This gives a 174v maximum output. ...

Maybe my power supplies are on the odd side, but with the volt adjustments minimized the whole works returned 167 volts, right on the money for safe pack charging/rebalancing as-is. I know 42*3+48=174, but there seemed to be extra adjustment room in practice with the units I received. I realize charging/rebalancing as it passes 165V or so would get rather slow, but that would minimize heat buildup. At 162V at least the power supply consumes the same full 63W it does at lower pack voltages.

Regards,
Roger

[aisbell]

Originally Posted by retepsnikrep

I'm sure the charger is doing some good.

I'm a bit concerned that without the constant current final power supply of your current charger design, my charger might be overheating my battery, especially during the initial charging. The input current is about 800 ma. which is considerably higher than what I have read might be an optimal output current. But I have no way to infer an output current from my measured input current.

Originally Posted by retepsnikrep

Do you have an Insight for use in Hawaii as well?

Unfortunately not. In many respects, I need my Insight more in Honolulu than in Uppsala because of the much better public transportation in Uppsala and Sweden, in general. Also, the extensive support for bicycle riding in Sweden has resulted in my biking in Sweden where I would have to drive in Honolulu (despite its much better biking climate, riding a bike in Honolulu means risking one's life sharing roads with heavy traffic).

But I will be spending fewer months each year in Honolulu than in Uppsala, so my Insight will be in storage for less time and at lower temperatures in Sweden which I hope will result in less battery imbalance problems.

Originally Posted by retepsnikrep

I'm sure you are doing this already but I would disconnect the 12v battery or even remove it during storage and switch off the nimh pack at the back.

Yes, I always remove my 12v. battery when I store my Insight. I store it on jack stands so the tires don't sit in one position for long periods. It has been stored in a pretty secure location in Honolulu, and car theft in Uppsala is not a big problem, especially for a weird car like the Insight But maybe I'll switch off the IMA battery this time (and hope that I remember to turn it back on in April

[Mike Dabrowski 2000]

I added a 1W white led in series with the charger. This does 2 things, first it drops an additional 3-3.6V, which allows the max final voltage to be brought to 170V or below, which I like better that the 174.
The second is that it provides visual current indication, so you know it is supplying current.