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Hello does anyone have a list of the resistors needed to ramp down a 32 A EPC?
Had one but lost it somewhere...Thank you very much!!
Or has anybody tried it with a variable one ? ( don't know the english name "potentiometer"?!?)
 

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I believe that they are called a variable resistor or rheostat. Certainly you can use one of those, too, provided that it supplies the proper range of resistance. Send an e-mail to [email protected] and we can get you the EPC manual which has the IC resistances in it.
 

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I believe that they are called a variable resistor or rheostat. Certainly you can use one of those, too, provided that it supplies the proper range of resistance. Send an e-mail to [email protected] and we can get you the EPC manual which has the IC resistances in it.
Thanks a lot!!! Seems like I found the right person for that topic!
 

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Hello does anyone have a list of the resistors needed to ramp down a 32 A EPC?
Had one but lost it somewhere...Thank you very much!!
Or has anybody tried it with a variable one ? ( don't know the english name "potentiometer"?!?)
Try here:
ZCW EPC "IC" (input current) Resistor Values table
and here:
How to add a Current Selector Switch guide

I'm using a digital potentiometer & micro controller, but if all you want to do is select current you're better off using passive resistors, or parallel networks of resistors to hit the exact values.
 

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Thanks a lot! And yes, first I wanted to do it the same way you did but then I thought , maybe it would be better making it with passive resistor and keeping it nice and simple and as reliable as possible. Because a lot of people, family and friends will use it and it would be better of the robust way! The parallel network won't be needed because I will mostly need only 2-3 settings. So, thanks again and have a nice day!
 

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Hi Paul, I am wondering about the use digital resistor and the microcontroller as we can use the passive potentiometer for this purpose. Is there any reason that you used the digital resistor like the advantages of using it as I think it will be expensive to use it?

electronic pcb assembly
 

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I installed a US$10 10K-ohm potentiometer onto the Mainpine EPC IC terminal, and it does the trick. The only trouble with this approach, however, is that it's difficult to know the exact setting. I have my own solution for that right now, but for most users I suspect they'll be better-served by a rotary switch:

https://system.netsuite.com/core/media/media.nl?id=111422&c=3562421&h=ba8edf6ed6aa7a123530&_xt=.pdf
The digital potentiometer IC cost me only 60p but of course it's more expensive than a switch when you take into account the micro controller. As @Lee Howard describes it's also really tricky to get the right settings. The accuracy on these things is actually pretty bad, and they're quite voltage sensitive so the resistance changes if you don't have a stable voltage. I've had to run the calculations then fine tune connected to an ohm meter. The data sheet states there is even variance between parts, so nothing is fixed! Unfortunately as the Mainpine EPC uses really quite low resistance values these small errors cause big issues. In my prototype I'm actually using two outputs from the potentiometer arranged as parallel resistors to give me the accuracy I want, and absorb some of the error and variance.

The only reason I'm going for this approach is that I want to vary the resistance to change the charge rate remotely whilst charging under control of a local and remote microcontroller in order to optimise solar PV usage for charging.

Well, not the only one - also for the sheer hell of it, as I'll get a cool 7-seg display with the charge rate on and its easy to add the ability to view, change, and report stuff from a web app as well. Why? who knows? Why not? This was a pretty silly thing to do, the part cost of the LED driver IC and the mini 7-seg display has massively increased component cost and my target of <20 mA power budget - though that went out of the window when I discovered the voltage sensitivity of the digital pot and had to incorporate a mini switch-mode PSU to get a solid 5V supply. :oops:

The sensible option is most definitely to follow @RickMGoldie and build a manual switch with fixed high precision resistors. :D
 

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Oh, and Hi @pilav - Welcome to SpeakEV!


Hi Paul, I am wondering about the use digital resistor and the microcontroller as we can use the passive potentiometer for this purpose. Is there any reason that you used the digital resistor like the advantages of using it as I think it will be expensive to use it?
 

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I'm planning to an on-off-on SPTD toggle switch. That would give me 32A + two other values. I'll probably choose resistors for 10A and 16A.


I just noticed that some of the IP rated on-off-on toggle switches on RS are incorrectly labeled. Double check the data sheets and part numbers.

Still deciding if I want to mount the switch on the outside of the box. I wouldn't want it getting bumped.


Or has anybody tried it with a variable one ?
I did consider it briefly but decided on a switch instead. I don't want to be risking over-current if I've got the knob in the wrong place.

You would want a linear potentiometer. 32A is 732ohms. Anything slightly higher gets into breaker-trip territory.

A precision 500ohm pot. with 220ohm resistor in series would let you dial in anything from about 8A to just under 32A. You need to choose parts that won't exceed 732ohms inside their tolerance ratings.

With a 2% potentiometer and a 1% fixed resistor, the worst case is:

500 + (.02 * 500) + 220 + (.01 * 220) = 500 + 10 + 220 + 2.2 = 732.2.

It is unlikely you will get both of them at the high end of the tolerance range but it can happen. The values will vary slightly with temperature, humidity and age. To be safe you could use a 215ohm fixed resistor.



Bourns make precision IP rated potentiometers but they won't be cheap. I spot checked Digikey for an IP-65 rated 10-turn 3590-4 series are about £11 each. 500ohms is not a standard value for this part. Might be hard to find a sealed IP-65 part in qty. 1. Might find one on eBay.

Digikey do the unsealed 3590S-2-501L but show zero stock. Might be possible to order just one.

Farnell have an unsealed 3540S-1-501L in stock --> http://cpc.farnell.com/bourns/3540s-1-501l/potentiometer-500r/dp/RE06827

You'd need an ammeter but could set the currents in small increments. Might be fun to play with. See my posts for some possible ammeters.

http://www.digikey.co.uk/product-detail/en/3590S-2-501L/3590S-2-501L-ND/1088591

 
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