amp questions for driving 'voice coil actuator'? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th October 2005, 04:50 PM   #1
steve is offline steve  United States
diyAudio Member
 
Join Date: Feb 2003
Location: wi
Default amp questions for driving 'voice coil actuator'?

Hi...

I am looking for an amp to drive a 'voice coil actuator'... During a conversation with an engineer for the manufacture I was told that they use a simple audio amp for 'testing' purposes to drive these devices, but I'm concerned that my requirements will place an intolerable load on an audio amp. In particular, I will be driving these devices at very low frequency... (expected frequency range will be 0.1 hz to 10hz) and with a DC offset to boot. Another significant problem with these devices is that they utilize a very substantial coil (one device that I'm considering has a 2 lb voice coil) and consequently produce significant back EMF. This same device has an impedence of 2.8 ohms and produces 100 lbs of force at 41 volts. I think that I will only require a small percentage of that force, but this motor has other charateristics that are important (for one... it's surplus). Anyway, my question is this, is there an audio amp design which would be appropriate for such a load, or should I look elsewhere?

thanks,
steve
  Reply With Quote
Old 4th October 2005, 04:58 PM   #2
bogicp is offline bogicp  Yugoslavia
diyAudio Member
 
bogicp's Avatar
 
Join Date: Oct 2005
Hi steve,

do you have any other specifications about your amplifier requirements... for example, output voltage, output current, maximum distortion, etc... ?

Best regards,

boggy
  Reply With Quote
Old 4th October 2005, 05:34 PM   #3
steve is offline steve  United States
diyAudio Member
 
Join Date: Feb 2003
Location: wi
to be honest..... no.

There is a very long (and mostly irrelevant) story behind this, but the short explanation is that I'm trying to build a device to introduce pressure waves (at low frequency) into tissue. I currently have a device called a 'foredom percussor' which is used for this purpose, but it is limited to a sine wave of fixed amplitude, with only limited control of frequency. I am interested in more complex patterns, and need to have more control of amplitude and frequency, in particular I am looking for feedback control.

I have found a 'voice coil actuator' which should be capable of reproducing the motions and power of the foredom device (at least the low frequency aspects), with the additional capacities that interest me, and it is this device that I mentioned in my previous post.

I would be happy to 'start out' with an amp that is able to produce a quarter of the force that the motor is rated for, I'd guess about 10 volts at 2.8 ohms, but at the same time, I think that this amp might need to deal with wildly unsymeteric swings as well as DC offset, and the back EMF will be horrendous at any sort of speed..

And the truth is that I'm just experimenting here, and I don't know what requirements I'll end up with... It would be nice to just get to a point where I could produce a simple sine wave with the contraption... but I am hoping to eventually utilize a linear transformer as a feedback device. I actually want to introduce a 'feedback' effect in the tissue

hope this helps,
thanks,

steve
  Reply With Quote
Old 4th October 2005, 05:49 PM   #4
bogicp is offline bogicp  Yugoslavia
diyAudio Member
 
bogicp's Avatar
 
Join Date: Oct 2005
hm, i don't know really, how some standard amplifier chip can tolerate currents returned from your device, but loudspeakers has same "practice"...

You can posibly try some "gainclone" project, it's widely available both at this forum, and at world wide web.
It's simple, inexpensive, and with other components (large power supply capacitors... for example) you can do anything with it...
They is like "power opamp", you can do DC with it, etc.
-Current limit is 7A typical
-and you can use +/-20V power supply
-if your currents are too high, you can do "parallel mode" configuration with two LM3886, and then drive low impedance with him...

Ok, I probably speculate only, but there isn't much more informations...



best regards,

-boggy
  Reply With Quote
Old 4th October 2005, 06:14 PM   #5
steve is offline steve  United States
diyAudio Member
 
Join Date: Feb 2003
Location: wi
Thanks again... I know that I didn't have much info to provide, but you actually addressed my major concern which had to do with the DC offset that I anticipate.... I actually have a couple of 3875's... not to good for the loads that I anticipate.. but I could try to parallel a couple.. Or I could look at the 4870(?)...

I just wanted assurance that I wasn't going to toast my amp by trying to drive such a crazy load.


thanks,
steve
  Reply With Quote
Old 4th October 2005, 06:22 PM   #6
bogicp is offline bogicp  Yugoslavia
diyAudio Member
 
bogicp's Avatar
 
Join Date: Oct 2005
try 3875, but instead of LM4780 (you probably have a typo) look at old LM3886, this chip has double power dissipation capability... and use two of it in parallel mode... then you will probably have much more time for your work, instead to build power amps all the time...


best regards,

-boggy
  Reply With Quote
Old 4th October 2005, 06:42 PM   #7
steve is offline steve  United States
diyAudio Member
 
Join Date: Feb 2003
Location: wi
I hear you on that one.... thanks again for your help

Steve
  Reply With Quote
Old 4th October 2005, 11:35 PM   #8
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
I would say this sort of driving capability is beyond a chipamp. I would build a discrete amp with a heavy output stage, probably switching mosfets. The emphasis here would be on the output stage having to provide lots of current and deal with quite a severe back EMF.

It might also be an idea to look at discrete, high current regulated power supply circuits. These are normally very similar to amps in design, but with emphasis on handling current.
  Reply With Quote
Old 4th October 2005, 11:46 PM   #9
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
I wonder if this would be a job for a class H type project? Or some type of modulating power supply for slow, high inductive loading. Or maybe a servo motor drive circuit? motor drives are quite common in industrial machinery.
__________________
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 5th October 2005, 09:49 AM   #10
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Just use four LM3886 in parallel with a 30-0-30 500VA transformer, a 25A bridge and a pair of 15,000F caps.

The LM3886 is protected against back EMF, and has all kinds of protection built in. Cheap too.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Some questions on dual voice coil woofers Fanuc Multi-Way 4 5th February 2009 11:58 PM
Single Voice Coil Vs Double Voice Coil Subwoofer Workhorse Car Audio 6 12th April 2007 06:36 AM
ASV voice coil ? Nihilist Multi-Way 4 1st October 2006 07:16 PM
Dual voice coil wiring questions devils_advocate Multi-Way 5 25th May 2006 12:37 PM
an amp for each voice coil? speekergeek Multi-Way 1 12th December 2003 02:31 AM


New To Site? Need Help?

All times are GMT. The time now is 06:22 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2