Use IMAX B8 RC-chargers instead of the built in one - possible?

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Frolle
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Joined: 05/11/2012
Points: 46

Hej.

I'm thinking of oredring 4 pcs of the IMAX B8 RC-chargers capable of charing 27 NiMH-cells in a serie.
Using IMAX B8 chargers I guess would be more gentle to the Vectrix batteries then the built in charger. The IMAX uses Delta V to stop the charging when a string is fully charged.
Are at the moment using a IMAX B8 to analyze an old pack, cell by cell, charge, discharge and it seams to work well there.
Yes, it will take more time to charge, since current will probably be around 5 Amps. This is OK for my daily needs, but if in a hurry, the built in "evil" charger will remain.

I do not know if the on-board computer will prevent me from riding if it does not know that batteries has been charged with external charger….?
Or will I just loose the bar-graph functionality? Nothing else?

I think temperature monitoring will not be necessary, since I could only recognize a very slight temperature increase during tests of my old cells with a 5A charge current.

Comments would be appreciated (before I scoot away and buy my chargers :- )

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Mik
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Re: Use IMAX B8 RC-chargers instead of the built in one - ...

Frolle wrote:

Hej....

I think temperature monitoring will not be necessary, since I could only recognize a very slight temperature increase during tests of my old cells with a 5A charge current.
.

I think you did not wait long enough for the temperature rise to occur.

If you charge the entire battery with 5A without active cooling, it will overheat once it is full. It will probably even overheat when it is actively being cooled.

However, you may also find that the charger does not put out 5A when charging 27 cells in series. I once had an Imax B5 (?IIRC) and it only put out the specified 5A when the number of in-series-cells was much lower than the maximum it could charge. I think it dropped to about 3A when the voltage got too high. Better check the fine print.

I am also concerned about the possibility of "ground loops" forming while the chargers are all running at the same time.

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ofx210p
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Re: Use IMAX B8 RC-chargers instead of the built in one - ...

Why not just use the lairds charger firmware which is proven to not heat the pack beyond 1 -3 degrees above ambient. Very gentle on the pack - very good. Other advantages keeps fans running whilst charging and fans run on for an hour (if you want them to) to give active cooling post-ride.

Cheers

Chris

Frolle
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Joined: 05/11/2012
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Re: Use IMAX B8 RC-chargers instead of the built in one - ...

Do not get me wrong, I am VERY impressed over The Lairds successful software modifications!

I will definitely flash my bike as soon as I lay my hand on a CAN-bus adapter, and figured out where to retrieve the software and the new flash-binaries.

But...
http://visforvoltage.org/forum/12321-latest-may-2012-software-instructions

"Allow the battery to charge fully occasionally or when you actually need that full charge, otherwise charge only to about 70% to 80%. (this is about an hour after the C.C. stage begins). This prevents higher leakage currents (which occur when the battery is 'full') which will shorten the battery life."

I do not have the possibility (do not want to) interrupt the charging-process every time, so that was when my idea of using four IMAX-chargers popped up.
imaxb8.jpeg
I do not know witch method that would be most gentle to the pack...?

Mik, hopefully it will not overheat since the Delta Peak recognition should stop the charging.

Mik
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Re: Use IMAX B8 RC-chargers instead of the built in one - ...

Frolle wrote:

"Allow the battery to charge fully occasionally or when you actually need that full charge, otherwise charge only to about 70% to 80%. (this is about an hour after the C.C. stage begins). This prevents higher leakage currents (which occur when the battery is 'full') which will shorten the battery life."
...

That simply means use a timer, which you should do anyway. The charger heats up and wastes a lot of energy when it remains plugged in after charging.

You also expose your bike to grid voltage spikes when it remains plugged in unnecessarily.

A countdown timer works well for this.

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HarryS
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Joined: 10/08/2008
Points: 341
Re: Use IMAX B8 RC-chargers instead of the built in one - ...

I think it is important to review many of the excellent posts that Mik put into the handbook. It will make you realize that this bike is build around its charger. You stop using it to charge the battery and the bike no longer knows what range to display. battery gauge will also not display anything useful. The Laids software, on the other hand preserves and extends these functions, giving you the option to display the current voltage of the battery in addition to an accurate state of charge display.
Using multiple chargers on sub strings of batteries is a bad idea. Theoretically possible but a bad idea nevertheless.I did ttest a Venom charger on - string of 9 Vectrix cells. The end of charge does not work well. The charger tried to pump 42000mA into the battery which inspire of a fan blowing on it heated up considerably.

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