Current limiting a DC gear motor

powerfull motors),

longer...

RCA used small Variacs and torque motors on both reels on their TP66

16 MM film chain projectors. If the fil broke, the arm hit its limit switch and turned off that motor. I reloaded and restarted the projectors before splicing broken film, while it was piling up on the clean waxed floor. I could reload and restart in under 10 seconds. A splice and restart took three minutes.

--
You can\'t have a sense of humor, if you have no sense!

Pulse Width Modulation. You can maintain full torque down to practically

0 RPM.

Regulate it with a tension sensor (a movable capstan, a spring, and a pot or even a switch or two) such that it simply takes up as much as it needs to.

PWM isn't hard at all, albeit being inexperienced, you could probably use some help with the design. Just use an ordinary NPN low-side current sink and pulse it at whatever rate it takes to maintain proper tension on the film.

I built a PWM circuit to regulate the speed of a 1.5A motor, with substantial voltage compliance (It's a "spool gun"

) that's expected to work from 24-40 volts input. Sadly, the product died on the vine because of manufacturing considerations. )-;

Good Luck! Rich

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Thanks Rich. Is PWM motor control based on a Pot input more accurate/ reliable than a DC voltage regulator based on a Pot input?

Lars

Absolutely. Torque is dependent on the current through the motor. Voltage regulation drops the torque at the time when you need it the most.

One caution - the time I did this it was with a permanent magnet DC motor - I haven't verified that it would work with a series-wound motor, but it sure seems logical to me that it would.

I say PWM simply because an analog current regulator would waste a lot of energy.

Cheers! Rich

Sloman

Umm, No they don't.

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Also true.

We use pots like this..

HALL types.

And Carbon types which last a very long time in a harsh environment!

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   Stop using Radio Shaft POTS!!!!!!!!!!!!!!!!!..

On my planet they do (the ones I use - budget ones)

In a distant past, I have routinely repaired Hitec servo's with exactly that problem. Servos were expensive. Nowadays I order them from HK for a few $..

pots=20

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You can try and build quality, or you can build cheap. Building real quality in the current era is really challenging because with so much Chinese production and marginal supply chain control over there it is not quite doable. Not even "trusted" suppliers are invulnerable to being fooled. It becomes a business question of how much returns can you afford.

? 2009?9?6???? UTC+

8??8:40:29?Lars Bentley???

Sell: China Shenzhen ZHAOWEI Machinery & Electronics Co. Ltd engages in designing , manufacturing and marketing all kinds of electric motors. They are mainly suitable for the following applications: smart home application used in sm art kitchen and laundry, medical instrument for personal care, smart E-tran smission applied in automobile, industry automation applied in telecommunic ation and a great variety of plastic/metal planetary gearbox in different s izes. In order to develop the oversea market, we are current seeking new partne rs around the world to create a bright future together. ZhaoWei is a right choice and excellent partnership with sincere services.

Company: Shenzhen ZHAOWEI Machinery & Electronics Co., Ltd URL:

Contact: Anny Liu Tel?+86-755-27322652 Fax?+86-755-27323949 E-mail: snipped-for-privacy@zwgearbox.com Add: Blk. 18, Longwangmiao Industry Park, Fuyong Tn., Bao?an Dist., Shenzhen 518103, Guangdong, China

Take a look at the part LM317 applications notes. The LM317 is a variable voltage regulater which can be used to make a constant current source.

In your case I think you would be better off with a proporsional control in stead of the Bang Bank control. Bang bang refers to a servo system that is either full on or full off. Admitted you want to switch betveen full on a nd a low current, but that is very close to a Bang bang servo sysmem. It o nly has two modes.

You can buy linear pots and connect one to the arm you mention in a later p ost. With a proportional control system the amount of current would vary from fu ll on to what ever value is needed to wind the tape on the spool.

Do not listen too much to those that say pots wear out. They will wear out but not quickly. They are used all the time in foot pedals for control of current in welders.

Dan

The Texas -Instruments app notes is at

Take a look at section 9.3.3 figure 14.

The LM317 should be adequate for the 24 volts and 1 amp you mention, but it should have a heat sink.

Dan

? 2009?9?6???? UTC+

8??8:40:29?Lars Bentley???

Sell: China Shenzhen ZHAOWEI Machinery & Electronics Co. Ltd engages in designing , manufacturing and marketing all kinds of electric motors. They are mainly suitable for the following applications: smart home application used in sm art kitchen and laundry, medical instrument for personal care, smart E-tran smission applied in automobile, industry automation applied in telecommunic ation and a great variety of plastic/metal planetary gearbox in different s izes. In order to develop the oversea market, we are current seeking new partne rs around the world to create a bright future together. ZhaoWei is a right choice and excellent partnership with sincere services.

Company: Shenzhen ZHAOWEI Machinery & Electronics Co., Ltd URL:

Contact: Anny Liu Tel?+86-755-27322652 Fax?+86-755-27323949 E-mail: snipped-for-privacy@zwgearbox.com Add: Blk. 18, Longwangmiao Industry Park, Fuyong Tn., Bao?an Dist., Shenzhen 518103, Guangdong, China

? 2009?9?6???? UTC+

8??8:40:29?Lars Bentley???

Sell: China Shenzhen ZHAOWEI Machinery & Electronics Co. Ltd engages in designing , manufacturing and marketing all kinds of electric motors. They are mainly suitable for the following applications: smart home application used in sm art kitchen and laundry, medical instrument for personal care, smart E-tran smission applied in automobile, industry automation applied in telecommunic ation and a great variety of plastic/metal planetary gearbox in different s izes. In order to develop the oversea market, we are current seeking new partne rs around the world to create a bright future together. ZhaoWei is a right choice and excellent partnership with sincere services.

Company: Shenzhen ZHAOWEI Machinery & Electronics Co., Ltd URL:

Contact: Anny Liu Tel?+86-755-27322652 Fax?+86-755-27323949 E-mail: snipped-for-privacy@zwgearbox.com Add: Blk. 18, Longwangmiao Industry Park, Fuyong Tn., Bao?an Dist., Shenzhen 518103, Guangdong, China

Put a 100 ohm, (at least 5 watt) resistor in series with the motor, and a switch to short out the resistor, like this: (view in fixed font)

+24 ---+---[100R]---+---[Motor]---+ | | | +-----o

Slide pot rather than rotary

China Shenzhen ZHAOWEI Machinery & Electronics Co. Ltd engages in designing , manufacturing and marketing all kinds of electric motors. They are mainly suitable for the following applications: smart home application used in sm art kitchen and laundry, medical instrument for personal care, smart E-tran smission applied in automobile, industry automation applied in telecommunic ation and a great variety of plastic/metal planetary gearbox in different s izes. In order to develop the oversea market, we are current seeking new partne rs around the world to create a bright future together. ZhaoWei is a right choice and excellent partnership with sincere services.

Company: Shenzhen ZHAOWEI Machinery & Electronics Co., Ltd URL:

Contact: Annie Liu Tel?+86-755-27322652 Fax?+86-755-27323949 E-mail: snipped-for-privacy@zwgearbox.com Add: Blk. 18, Longwangmiao Industry Park, Fuyong Tn., Bao?an Dist., Shenzhen 518103, Guangdong, China

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