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Old Aug 10, 2013, 05:02 AM
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switching from lipo to nimh

Hi,ive recently bought a perkasa boat that runs on four 7.2 lipos and brushless motor,i want to change this to two 9.6 nimh batteries would i need to do anything to the speed controller,ive tried it and all that works is the rudder and sounds like a fan on the speed controller,thanks in advance for any advice.
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Old Aug 10, 2013, 06:56 AM
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Four 7.2 lipos? How are they connected?

Dave
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Old Aug 10, 2013, 08:13 AM
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Dazzo- if the 4 LI-POís are connected in series you will be running on 14.4 volts of power. If you connect the two NI-MH batteries in series you will be running 19.2 volts of power. First find out what your speed controls top voltage is rated at. Second you may have to re-program you speed control for the correct cut off voltage for discharge on the different batteries.
You may also have to reprogram the speed controlís throttle settings in order for the speed control top see neutral, full power ahead, and reverse.
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Old Aug 10, 2013, 04:58 PM
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Let's see your setup first.

What size batteries do you have?
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Old Aug 10, 2013, 10:06 PM
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I have never messed with Li-po's but I think if you have 4, 7.2 volt Li-po's in series that would be 28.8 volts?
John R.
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Old Aug 10, 2013, 10:18 PM
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I am sorry to say that I miss spoke about the voltage thinking in terms of 4 LI-PO cells at a LI-PO cell rating of 3.6 volts per cell. When I re-read the first post I see now you had four 7.2 volt LI-PO batteries which is 8C or 28.8 volts. Running two NI-MH battery packs of 9.6 volts (8 cells) you would be running at about 2/3rd the power of the LI-PO batteries at full speed.
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Old Aug 12, 2013, 04:15 AM
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Thanks,dont mind a loss of power as its a bit too fast,will get a pic later as im fairly new to rc and have no idea how to re set it
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Old Aug 12, 2013, 02:08 PM
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hi,the speed controller is a Hobbywing rtr version 2-4s lipo 3A@5.75v super bec
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Old Aug 12, 2013, 02:13 PM
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Old Aug 12, 2013, 06:55 PM
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If the new nimh pack voltage is far below the cutoff voltage currently set in the esc it will never run. The esc thinks you have a dead pack. You may need to reprogram the esc to turn off the low voltage cutoff, or at least set it to a voltage that works for your new pack.

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Old Aug 13, 2013, 03:27 AM
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Thanks Dave,how would i reprogram it?
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Old Aug 13, 2013, 12:48 PM
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Most esc's have a setup button(s) somewhere, and there is a sequence to be followed to make any user setting changes. The instructions would be very helpful here. If there is no button, or connection port of any kind, then chances are that you cannot make any changes and would be stuck with the recommended battery configuration.

Dave
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Old Aug 14, 2013, 05:04 PM
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Thanks Dave,so if i change the speed controller to a regular one would i also need to change the motor as well?
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Old Aug 14, 2013, 06:46 PM
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The motor and esc are only related in that the esc must be able to deliver the correct volts and amps to the motor. You should be able to replace the esc with another of similar capabilities. But that doesn't help you in this situation. The motor was chosen to run at a certain voltage for a reason. If you are going to swap out a battery for another of very different voltage, you must consider the prop, esc and power supply as a system. All the components must work together to get the job done. And to get the same job done, a system working at half the volts will require double the amps (ohms law).
Now, looking at your original post it appears that you are trying to swap a nimh pack for a lipo pack. Is there a deeper reason for this?

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Old Aug 15, 2013, 01:58 AM
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Thanks Dave,the main reason for changing is that i dont really want lipos in the house,heard horror stories etc,ive got nimhs in my other boats.
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