| mikecr |
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Reply with quote | #1 |
Tuning a Chargemaster
I really like the Chargemaster 1500 system. However, one common issue(with some powders and systems) is that about 1/3 of it’s dispenses overcharge by .1gr or more. This occurs as a result of poor rate control by the microcontroller(within the scale). It can be predicted when dispensing hits the setpoint prior to speed reduction to the slowest-trickle speed(there are 3 speeds). My goal was to force trickle speed in every charge, eliminating overshoots. Also, I am willing to accept a reasonable cost in speed for further accuracy.
I do not have the ability to communicate with the H8/3487 microcontroller. So adjusting the PID parameters was out. I thought that modifying (deepening) the charge tube threading would help smooth out the powder rate, and allow better control. That turned out to be true, but didn’t resolve the overcharging problem. I monitored voltage and current to the motor, and found late and high rate coast down to lower speeds due to bad system tuning. This, I could influence.
My approach was to install resistance in the motor feed, slowing the motor just enough for the controller (as programmed), and scale (with it’s sample/settle speed) to really work together well. For my system, 3.3 ohms in line turned out to be the perfect value while dispensing IMR4895. Speed reduction was not really noticeable except an added 5 seconds or so to lock in right near the setpoint.
It stood to reason that different powder types might require slight tweaking of motor speed for peak performance. So I replaced the resister with an accessible 10 ohm potentiometer. I epoxy’d it to the inner wall, and drilled an access hole for it. In use, I punch in a charge, and while dispensing, adjust the pot up until the motor noticeably slows and nearly stops when at second speed. This is usually within a few grains of setpoint. Then I turn the pot down until dispensing continues and is just adequate for the slowest trickle speed. This is where the motor is bumping for a few grains at a time. With this setting, I verify no further dispenses hang up or overcharge.
I’ve been comparing charges against my D-Terminator(original). It’s a great reloading scale, but I wish I had a more serious scale for testing. Anyway, overcharges simply do not happen any longer as far as measured and remeasured from these scales. And that is a definite improvement for me.
I realize this isn’t an ideal DIY mod. You may not be equipped to do soldering. But I thought I’d throw it out there. If you have this issue with your system, it’s driving you nuts, but you can’t do this work, get with me & maybe we can work something out. Take care.
Mike Crawford
Mcrawford@ec.rr.com
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| Travelor |
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Reply with quote | #2 |
After considerable communication with RCBS, I am awaiting my 3rd unit. Supposedly it will be bench tested by their tech prior to shipment.
Anyone have the instructions to "fix" the high/lo speed parameters? They have never mentioned to me a "software" fix that the user may perform.
Mike, which model # of the potentiometers did use use and which of the three leads were used? Your picture seems to indicate the $3.00 model and the rear two leads.
Thanks Mike,
George
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| mikecr |
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Reply with quote | #3 |
I just grabbed one from a drawer in the garage. But you can use any of these in 10 ohm:
http://www.surplussales.com/Potentiometers/PCM-MultiTurn/PCM-MultiTurn-1.html
Mine is a 10turn, but the 24turn trimmers would work even better. I use the last 2 leads from the adjustment screw. But you can use either. If last 2, clockwise adj= slowing, If first 2, clowise adj=faster.
This isn't what I would call a "FIX", I didn't mean to imply that. But it did improve my system. Apparently, other systems such as that tested by this site, are way more accurate than mine. So maybe an RCBS replacement would be a better answer. I didn't try replacement as I assumed the unit worked as designed. It just wasn't perfect. What can I expect in this price range.
My testing isn't scientific either, as my compare scale is no more accurate. But I could watch a pinch of powder fall after the unit stopped. These occasions always measured high when remeasured. Now it doesn't do that.
It may very well come down to the powder being used.
I would also like to know of any program access(such as the speed change point mentioned). |
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| Travelor |
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Reply with quote | #4 |
I sent the following email to RCBS today after getting my 3rd Chargemaster with the same problems, although so far this machine seems to be some better:
"The ChargeMaster seems to have a problem that causes it to throw a powder charge varying from exactly the desired charge up the .3 grain over while displaying the desired weight. The 6mmBR.com Forum mentions that the problem may be that the scale cannot keep up with the dispenser, resulting in the overcharges, and that a software problem causes the scale to reflect the desired weight.
I have spoken with Mr. Don Legg and he is aware of the above problem being reported.
The 6mmBR forum discussion indicated that there is "fix" by the user typing in a code on the keypad that will slow down the last potion of the charging cycle, thus allowing the scale to keep up with the dispensing. If this is so, can you give me some assistance with this procedure?
Love the ChargeMaster, but hate this problem"
We'll see what the reply is and I'll report to the Forum,
George Toney
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| Travelor |
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Reply with quote | #5 |
As of today still no response from RCBS. I have again emailed them with the same request.
George |
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| Travelor |
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Reply with quote | #6 |
Last week RCBS sent an email stating that they were referring my email to Mr. Legg and the Customer Rep Supervisor. The email asked for my phone number so they could call.
As of today still no response. |
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| lcbcp |
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Reply with quote | #7 |
OK, Mike...to get into the programming mode...after the read out shows 0.0, hold the EDIT/MEM key and the ENTER key down at the same time. Make any changes at your own risk. Different versions have different number of variables showing. If you write down all variables available in order you will see a pattern. If you have any programing experience, changing variables is obivious, if not I suggest not playing wih machine. Good luck. Last warning MAKE ANY CHANGES AT YOU OWN RISK. |
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| dreever |
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Reply with quote | #8 |
Everytime I think about buying an electronic scale and/or powder dispenser I read things like this and just look at my old 1010 and resign myself to being slow. It's sort of the tortoise and the hare fabel isn't it? I'll take accuracy over speed any day. |
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