Help with finding an electronic variable resistor
Help with finding an electronic variable resistor
(OP)
Hello everyone, i need to find a place where to buy (or where to buy the necessary parts and instructions) for an electronic varible resistor. In order to nake a series of tests in some batterys, i need to keep a constant current, and was looking forward to makeing a program which would change the resistance of such device (which would be connected in series with both the battery and load), but in order for that to work i need a variable resistor which could interpret the signals via an RS32 port or something alike. If ANYBODY knows anything, please let me know. Bye
PS: i need one that can go for several hundred ohms, the load is between 5kW and 20 kW, with a 48/24 source, so you guys can imagine the size of resistor i would actually need.
PS: i need one that can go for several hundred ohms, the load is between 5kW and 20 kW, with a 48/24 source, so you guys can imagine the size of resistor i would actually need.






RE: Help with finding an electronic variable resistor
Building something more adjustable than that may not be practical/possible.
RE: Help with finding an electronic variable resistor
1 How constant does your load need to be? Does it matter if current changes 1 %, 5 %, more, less?
2 Are transient deviations allowed? Say 10 % for 100 ms? Or is that too much? One percent for 1 ms? Please specify.
3 Do you absolutely need a resistor - or is regeneration into mains a possibility?
4 Is this a one off thing or do you need to produce many devices like this?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Help with finding an electronic variable resistor
http://www.analog.com/
and search for "variable resistor"
RE: Help with finding an electronic variable resistor
I have reservations whether AD will have anything capable of dissipating 20kW, unless you know better?
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Sometimes I only open my mouth to swap feet...
RE: Help with finding an electronic variable resistor
To SKOGSGURRA: the current can have a +- 5% difference, and about 10 % for 100 ms can be considered as a max.
RE: Help with finding an electronic variable resistor
RE: Help with finding an electronic variable resistor
RE: Help with finding an electronic variable resistor
But, there will be heat. And large resistors. Such resistors are available - google "starting resistor" or "power resistor". If you are happy, you will find them on eBay.
Regeneration is a better. You can do that using any old thyristor rectifier capable of the current. The voltage adaption may seem less-than-optimal - and it is. You could use a transformer between thyristors and mains for that. But I wouldn't say it is necessary.
Select a thyristor rectifier with digital control and RS232. You can then set wanted current via the serial interface. You can also (normally) read back actual current and voltage via the serial link.
This will usually give you something like 1 or 2 % accuracy and less than 15 ms step response.
And, do not forget to put a heavy diode in series with the rectifier. That is to protect battery from getting a gigantic overcharge if anything goes wrong.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Help with finding an electronic variable resistor
I agree with Skogsgurra's resistors + contactors + PLC solution.