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Post by ssstonelover on Oct 22, 2007 19:59:13 GMT -5
Hi Guys,
I'm looking for 500K no-load pots. I see the Fender 250K type advertised, and I've seen how I can make my own no-load pots, but the deal is that I might need ~300/500 of these babies so would need a commercial source, and I've been striking out so far.
Any help steering me in the right direction would be appreciated.
Bill
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Post by JohnH on Oct 23, 2007 2:14:30 GMT -5
Hey Bill - With over 300 pots, that must be one mutha of a complicated guitar! John
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Post by gumbo on Oct 23, 2007 9:43:22 GMT -5
Bill...if those quantities are really serious, talk to Harry at Hongkongsuperseller on eBay...nice guy who doesn't get phased by numbers.. :-)
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Post by ssstonelover on Oct 23, 2007 11:42:27 GMT -5
Hi guys,
Inspired by guitars for sure, but so far I've been using standard 500K and 250K on my personal guitar projects...one of which is still on the bench
... In my day job I work for a company making/designing electric scooters and we have one which needs a variable speed control independent of the throttle (with a limiter -- variable governor if you will) like on a mobility scooter and the circuit needs a wacky value, 680K to go through its full sweep of no speed (fully grounded out) to fully open. A 1M pot give lousy sweep (mainly full open) and and 500K clips the high speed ever so slightly. I'm thinking the no load 500K will get us what we realy want, with no clipping a the high end, and a reasonable taper at the low end.
We'll put a mesage in with Harry at Hongkongsuperseller, and see what happens. His usual lot size is about 1000 pcs, so a lttile over our needs, but we will see.
Any other suggestions to try?
Bill
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Post by wolf on Oct 23, 2007 12:04:00 GMT -5
I'm curious if the potentiometer circuit for the scooter uses 2 wires or 3 wires. If it is wired like a tone control (2 wires), it will do what you want. However, if it is wired like a volume control, (3 wires) then it still will put a load on the circuit and won't be truly full-on.
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Post by sumgai on Oct 23, 2007 15:51:24 GMT -5
stony, Try different tapers for that 1MΩ pot. If that starts gettting closer to what you wanted, then you can modify the pot's overall resistance, and co-incidentally modify the taper at the same time, by adding a resistor between the wiper and one leg or the other. There used to be a thread on this forum about that very topic, modifying a pot's taper, but somehow the search function seems unable to find it........... Ask, if this doesn't make sense to you, and we'll see what we can dig up. sumgai
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Post by ChrisK on Oct 23, 2007 18:10:07 GMT -5
Bill,
Bear in mind that searching for 680K may be unproductive in the end.
The typical carbon pot has a tolerance of +/- 20% (for a quality one) to +/- 30%.
This means that the 680K pot will measure in the range of 550K to 810K. This isn't an indication of a defect, just the reality of production tolerances.
One CAN get potentiometers that are much more accurate, they're just much more money.
The key is to not depend on the absolute value of the resistance, but the precision of the ratio. In other words, use the pot in a reference-based mode as a three-wire ratio generator.
As an OEM embedded design engineer for 30+ years, personally I'd never use a pot of the quality used for a guitar (or amp) in anything that involved liability (people/moving objects/brick walls/etc.).
This all presumes that you are using analog controls. With a micro-controller, absolute value is never an issue since ratio's rule.
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Post by ssstonelover on Oct 24, 2007 2:48:41 GMT -5
Hi guys,
Wolf, I'll double-check if we set it up 2 or 3 wire. I believe 2 wire...
Sumgai, good points, about finding other taper, or 'creating' one through an added resistor. Let me see tomorrow if I can get some traction using those ideas. Who would be a good source for various tapers?
ChrisK, Hm...ratios, makes sense, as does using a bettter grade of pot. The motor controller itself is composed of some chips, FETS, etc. Let me throw this to our EE, but since other interface parts (like throttle use simple hall sensors, analog might be what I have.
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Post by ssstonelover on Oct 25, 2007 14:01:59 GMT -5
Hi guys, here is the update:
We threw in a 10Mohm resistor (also tested a 2Mohm) per Sumgai's suggestion and had what we considered a good balance of sweep, w/o undue speed clipping at the high end, or undue no speed sweep at the low end. Very cool. Brought the pot down to about 800K overall. Interesting how these ideas work in many contexts, and how versed you all are in the bigger electronic picture.
PS:
--Wolf: was a 2 wire set up...
--ChrisK: I hear you, but I think we will be OK with this simple modified pot now. Main control is still through throttle, so this pot is more a user adjustable governor than anything else.
Thanks, Bill
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Post by ChrisK on Oct 25, 2007 14:39:44 GMT -5
So who is it governating? ;D
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Post by sumgai on Oct 25, 2007 15:02:29 GMT -5
So who is it governating? ;DGovernate this, sucker!
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Post by ssstonelover on Oct 25, 2007 15:05:13 GMT -5
I do live in California, land of the governator... good joke. thanks.
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Post by ChrisK on Oct 25, 2007 17:35:38 GMT -5
It just seemed like a moxieoron.
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Post by JFrankParnell on May 9, 2011 17:10:55 GMT -5
My old man just got a mobility scooter, and it does have this guv'nah dial there on the dashboard. SSS, what brand are yours? I (and the old man, he did play a little gtar in younger years) would be interested to know if the tech on his scooter came from guitar guys
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Post by ashcatlt on May 9, 2011 19:43:46 GMT -5
Wonderful old thread. Sure hope they've made millions since! :/
Why, in a company which ostensibly has a real EE getting paid, did they come here for help?
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Post by sumgai on May 10, 2011 0:37:33 GMT -5
Why, in a company which ostensibly has a real EE getting paid, did they come here for help? I've been on both sides of this particular fence. When start-ups are still small, it happens that no one is a true engineer. They might be nerds, or "merely" technicians, but they can still get the job done.... though without that all-important signature. Enter the Professional Engineer (cue the Godzilla music), a glorified consultant who is called in to sign off on the thing. Which means that she/he will re-design it to their own spec, sign off on that, and the thing gets its UL listing*. Afterwards, the nerds go back in little steps until they reach their original design, and the product ships with some kind of profit. HTH sumgai * You all do know that the UL does not approve of anything, right? They only recognize parts and subassemblies, and list final production asemblies/products. That way, they can't be held liable for when a part/product pulls an Epic Fail - after all, they didn't really approve it or anything, they just made an entry in their database (for which they charged a princely ransom).
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Post by gumbo on May 10, 2011 8:30:16 GMT -5
* You all do know that the UL does not approve of anything, right? YIKES! ...you mean, all these years I thought........ ...just as well we double the voltage over here to make sure there's no evidence left after it all goes pear-shaped....
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Post by sumgai on May 10, 2011 12:38:53 GMT -5
* You all do know that the UL does not approve of anything, right?
YIKES! ...you mean, all these years I thought........ Ah, I see you've been cutting back on your meds again - it's obvious whenever you use the word "think"..... Yes, I can see where you'd call it pear-shaped, being uside-down like that. But up here in the correctly-positioned world, whenever something goes BOOM!, we call it mushroom-shaped. Now watch, some hob-nailed-boot wearing Godwin-reference wannabe is gonna come along and chastise us severely about the head and sholders for yanking this thread so far off topic. ...... Ya know, we should have Brownie points or something for those who specialize in such damage (the off-topicness, not the hob-nailness) - that'd be awesome! ;D sumgai
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Post by gumbo on May 11, 2011 7:33:27 GMT -5
There was a topic... ? g-f-b
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