potentiometer question

[gansho]

hey guys,

originally I was going to use 4 drivers on my fixture (hlg-185h-c1050b), but I've switched to 3 (hlg-320h-c1400B) to wire up 12 QB288V2's


So, four qb288v2's on each hlg-320h-c1400b


I had already ordered the 25k ohm potentiometers because I was planning on wiring the 4 hlg185s together to one dimmer.


Now do I need 33.3k ohm pots with the new config?

[LEDG]

You bet.

[Futuregrow]

I'd advise going for a B50K / B503 pot

[gansho]

now I am confused. what is a b50k/ b503 pot?

could someone link the appropriate pot?

is this one good?

[Futuregrow]

Refer to this thread, my post at the end will point you in the right direction:

viewtopic.php?f=27&t=1073

[DaveJonesFan]

My opinion would be grab 3 of these 10 turn precision 100K ohm pots, with 5% +- tolerance instead of 10% like most cheaper ones, you could also grab (3) 5K ohm resistors if you want to guarantee you can max out each driver. Put one on each driver.
https://www.ebay.com/itm/3590S-2-104L-1 ... 2447655?ss

Alternatively it could work with the 50K ohm model # 3590S-2-503L wired up to all three drivers with plenty of precision but the driver end would max out before the end of the dial presumably, and leave a dead spot.

Here's the datasheet for 'em:
https://www.bourns.com/pdfs/3590.pdf

[gansho]

ok well im trying my best to understand this all but I heres my situation:

I have 25k ohm pots because I intended to wire 4 drivers together but because I changed my setup a little bit, I only need 3 drivers to wire together, hence now needing different pots.

1- What would the result be of using the 25k ohm pots that I already have to wire up the 3 drivers?


2-Can I use the 25k ohm pots that I already have and then wire in an 8k ohm resistor to achieve the 33 total, similar to the 30k ohm pots with a 3k ohm resistor?


4 qb288v2 : 1 hlg320h-c1400b
3 hlg320h-c1400b : 1 dimmer

[sdfoster22]

Measure the resistance of the 25kohm pot. If it's a true 25kohm pot, an 8kohm resistor will work. Some cheaper pots have a 10% tolerance or more, so it might be 27kohm, or 23kohm.

If you just use the 25kohm pot. You'll get to about 75% of max.

If you wire the resistor in series to reach 33kohm you will reach max. It just takes the resistance from the bottom and adds it to the top. 15-100% dimming instead of 0-75% dimming.

[DaveJonesFan]

Good idea to take a deep breath. Honestly, you are confusing me when you keep referring to 'pots' (plural) as if there are multiple 25K ohm potentiometers that you have purchased and intend to use, however your intended configuration parameters which lead you to choose the 25K ohm pot are based around using one pot hooked up in parallel to all of the drivers, and you only seem to be building a single luminaire.

First choose if you really want 1 pot total or 1 pot per driver.

If one pot per driver, you need (3) 100K ohm pots.

If you want to put one pot to control all 3 simultaneously, then you need a single 33K ohm. 100/3 is all that is.

No potentiometer is a perfect device, so they have tolerances for being over or under. If you buy a cheap pot and actually measure it, it may not reach it's full rated spec. That's where a resistor can help bridge the gap, if it is deemed by you to be actually required to achieve your intended design goals. If your pot measures 99 out of 100K ohms, you might not really be bothered enough to correct, as you might not even intend to use the light at 100% brightness or care that the driver output is not reaching it's exact full energy potential. On the alternative, you may be wishing to get as much energy out of this light as you possibly can.

I recommend high quality pots that rarely need a resistor or if they do, the gap that they are needing to overcome is smaller. The pots I recommend also have much more precision because they are 10 turn implementations meaning you have to turn the dial fully 10 times to go from zero to full resistance. That may be overkill for your use as you can still get fairly good resolution out of a single turn pot.

There is documentation where Meanwell, the driver manufacturer, espouses the use of one potentiometer per driver for absolute best practices. Many choose to utilize the mathematical reality that you can avoid that cost and complexity and implement your own design goals.

Personally, using a 25K and a resistor sounds more hack than I would want, I like the resistor for the overcoming cheap pots concept, not for attempted overcoming of having selected the mathematically wrong part. You'd be purposely screwing with your usable range in this particular conceptualization of an 8K ohm resistor with a 25K ohm pot, as sdfoster22 mentioned. If you are intending to spend the least possible to get something up and working, then go for this option, but, rully though, the pots i linked are like $2 shipped.

Using a single 50K ohm 10 turn pot would allow the full range of outputs the driver can supply, with plenty of resolution as well, even though the end would create a dead spot where once you have reached the point on the dial where 33K ohms are seen by the driver, turning it further will not change the output. There is not a 33K ohm version of that high end pot available, unfortunately. Hence the secondary recommendation in my post in that direction. Single turn pots with dead spots can drastically reduce your resolution in the usable area of the dial, so you would probably want to avoid a 50K ohm single turn unit.

[Futuregrow]

I've ordered a considerable range of different pots and have experimented with them, and I can say every cheap pot I've ordered does meet the resistance range specified. As has been said, a 50kohm pot will do the job fine. I don't really agree about the resolution aspect because who's seriously trying to adjust their light brightness that finely? In this use care scenario, everyone's just trying to turn their light "down a bit" or "up a bit", in which case a basic 50kohm pot will work just fine.