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Using the Wild Thumper controller to charge large (10 ah) NiMH battery

I've recently upgraded the battery on my Wild Thumper and I wanted to get advice and warnings on charging a larger pack.

http://www.all-battery.com/one72v10000mahnimhbatteryforaerobirdxtremercairplane.aspx

The battery fits snugly into the thumper chasis base, and seems like about as much power as I can get without moving to LiPo.

I'd like to be confident in letting the battery sit charging unattended.

Questions:

If the charging circuit is rated at 2 amps should I assume that a depleted battery will take 5 hours to charge?

 

Since the default code monitors the voltage repeatedly every second and cuts out if it hasn't changed in 5 minutes, can I assume that is appropriate for this large pack as well? Or should I increase that timeout?

 

The docs say "The battery monitoring circuit will report a value of approximately 65 for every volt measured across the 

battery." Can this be modified? Should I be worried if I'm seeing values like 570? ( ~ 8.8 v)

 

Thanks in advance!

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As always I appreciate your speedy responses!

OddBot's picture

The size of the battery does not matter, bigger is better even if it takes a little longer to charge.

The value of ≈65 per volt is a result of the voltage divider built into the controller so that the analog input isn't damaged. You need to use a multimeter to measure the actual voltage and adjust the code as necessary since resistor values can vary by a few percent from board to board.

When charging, the voltage across a 7.2V NiMh battery pack can get up to around 9V depending on the charging current. My sample code monitors the battery voltage and when it begins to drop or stays constant for more than about 15minutes it assumes the battery is full.

You can modify the sample code if you wish. Read about how to recharge NiMh batteries here:
http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

Adding a temperature sensor may be a more precise way to monitor the battery charge as NiMh batteries have a a very small ΔV/Δt which is why my sample code cuts out if the voltage stopes rising after a certain amount of time.

As your new battery pack is bigger than the 4700mAh pack I tested my code with you may need to experiment a bit.