Potentiometers in series?

[AutoNub]

Hello! I'm controlling a current by changing the resistance using a 10 turn, 10k ohm potentiometer. However, it doesn't give me the precision or amount of control I'd like on the bottom end (for example, from 5mA to 2A out of a total of 52A). The slightest amount of pressure on the knob will change the amperage, which makes it virtually impossible to control with such precision. So I'm thinking I can add a 100 ohm potentiometer in series with the 10k ohm potentiometer (or in some other configuration using the two potentiometers) to give me the 10 turn variable resistance I need to precisely control the amperage on the low end (as described earlier).

Does anyone have any idea how I can acheive this? Using a PLC or other expensive devices/components are not an option. I'm hoping to find the right configuration with the components at my disposal, but I could incorporate new components if they are very cheap.


More details:

The configuration I am currently using with the single 10k ohm potentiometer is shown here (on the bottom right of the second page).

Here's an image of the configuration currently being utilized with my 50A power supply (as shown in the above link): see attachment.



Thanks in advance for the assistance!

 

[MrAl]

Hi,

From what it looks like you should be able to connect a pot in series with that pot terminal 2.
If the pot is 100 ohm that will give you finer tuning, although these kinds of arrangements are a little bit strange to adjust because you have to turn the little pot all the way down then turn the big pot so that its resistance is lower than needed, then turn the little pot to try to get the right adjustment, and if you run out of range with the little pot you need to turn the big pot again, then turn the little pot again. It does work though.

 

[Reloadron]

I would suggest you measure between pins 2 (common) and 7 (+) voltage and note the linearity. Actually 0 to 10 volts is what gives you 0 to 50 amps. With a 10 turn 10 K pot that is 1 volt (10 Amps) per turn. This makes it sort of difficult to split amps and milli-amps. You may want to try a high quality linear 20 turn 10K pot if you can get one.

@ MrAl, won't placing a fixed resistance on the bottom remove the low end control?

Ron

 

[MrAl]

Hi Ron,

Hey you posted three seconds after mine

Actually from his diagram it looks like this is a simple variable resistance set up, where the resistance gets either smaller or bigger as the pot is turned.
I dont think he'll loose any adjustment range because he can always turn the pot to 0 ohms, and that will zero better than the big pot probably.
Make sense?

 

[canadaelk]

The 100 ohm pot will give you only a +/= 0.5% range. Consider 200/500/1k pots. E

 

[Reloadron]

My bad, I was seeing a fixed 100 Ohms hanging down there.

Ron

 

[MrAl]

Hi,

canadaelk:
I see he had a 10 turn 10k pot and so each 360 degree rotation is like a 1k pot, so i figured he wanted something better than that.
100 ohms is 1 percent of 10000 ohms, so i thought that would allow him some very fine adjustment.

 

[Jackdaniel]

u cant use series pots! R u all gone mad? What the hell..

 

[crutschow]

u cant use series pots! R u all gone mad? What the hell..

Of course you can. Why in hades do you think otherwise?

We are sane. How about you?

 

[Reloadron]

u cant use series pots! R u all gone mad? What the hell..

Sure you can, exactly as canadaelk provided in a drawing. I have attached the same drawing.

Am I mad? No, actually I am in a great mood. The wife left for a few weeks in Arizona yesterday. Just me, the dogs who I must keep alive and a fridge full of beer. Hell no, I am not mad, more like a content happy person.

Ron

 

[Jackdaniel]

what the hell.. U cant use pots in series! What the hell.. Bet me u cant

 

[carbonzit]

Am I mad? No, actually I am in a great mood. The wife left for a few weeks in Arizona yesterday. Just me, the dogs who I must keep alive and a fridge full of beer. Hell no, I am not mad, more like a content happy person.

So the dogs are gonna drink beer, and you're going to eat dog food?

Wait, that can't be right ...

 

[ghostman11]

happy and content untill you discover the lock on the fridge and the wife has the key next time the wife is off on a trip let me know and i will send mine to keep her company

 

[Reloadron]

Hi Ya Ghostman

Strange you posted. I believe we know potentiometers can be placed in series for coarse and fine control. That said...

The wife's trip went well and I took the day off when she came home. This allowed an entire day to actually clean the house. She returned home to a clean house and the dogs were actually still alive.

I have been working on a temperature blog and much of the blog images take place on her kitchen table not to mention the stove used as a heat source. Hey, some thermocouple testing was in order. I was informed the kitchen table needed cleared and if I screw up the stove this will be my first and last blog, additionally life as I know it could change drastically. Go figure huh?

Ron

 

[ghostman11]

yeah women have some strange idea's!!! i got mine a new vacume for her birthday and she has the cheek to say i have no romance!!! she complains how the washing up ruins her hands, so i buy her washing up gloves and she throws them at me and goes off in a strop????? i wish they came with a datasheet!

 

[davenn]

To be honest, I was also thinking what the heck .... controlling current with series pots ????

they are going to have to be substantial hi wattage wire wound pots, else they are gonna cook really fast !
read the OP's first lines...

Hello! I'm controlling a current by changing the resistance using a 10 turn, 10k ohm potentiometer. However, it doesn't give me the precision or amount of control I'd like on the bottom end (for example, from 5mA to 2A out of a total of 52A).

He has a PSU of some sort capable of 52A, he's wanting a pot to be able to series pass up to 2A. No carbon tracked pot is going to be able to do that without burning the track.
Current limiting is done with pots, yes, but not directly, they would normally control other circuitry

cheers
Dave