# AC Drive SCR Swap **URL:** \ **Category:** Conversion Kits\ **Created:** [June 5, 2008, 7:24pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716 "2008-06-05T19:24:59Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![etischer](https://avatars.discourse-cdn.com/v4/letter/e/85f322/32.png) [@etischer](https://community.electricforum.com/u/etischer)\ **Post date:** [June 5, 2008, 7:24pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/1 "2008-06-05T19:24:59Z")
I bought a Eurotherm / SSD 2 horse Variable Freq. Drive which can run off a 300vdc bus. Im planning on using the brains and scr firing circuit to fire an external SCR pack to run a 40 horse motor. Any one have experience doing this? I’d also have to swap or modify the current sensing coil for the drive to get accurate current feedback. Anyone have experience doing that? You may ask why I don’t just buy a 40 hp drive. Well, Im cheap, and thought If I could make a 2hp drive into a 40hp 230v drive, maybe I could eventually make a 200hp unit. If i can’t make it work, I can use the 2 horse drive to run a 2 horse motor to run accessories like alternator and power steering, water pump… 1750 rpm would be enough speed to make power steering work atleast. ---
**Author:** ![Sir\_Joab](https://avatars.discourse-cdn.com/v4/letter/s/7bcc69/32.png) [@Sir\_Joab](https://community.electricforum.com/u/Sir_Joab)\ **Post date:** [June 5, 2008, 10:30pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/2 "2008-06-05T22:30:39Z")
If you’re planning on running DC into the SCRs, I don’t think it will work. An SCR is an avalanche device; once it’s triggered it will use the current flowing through it to latch itself on. The SCR won’t unlatch until the current flow stops. You might be able to do it with MOSFETS though. ---
**Author:** ![etischer](https://avatars.discourse-cdn.com/v4/letter/e/85f322/32.png) [@etischer](https://community.electricforum.com/u/etischer)\ **Post date:** [June 5, 2008, 11:45pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/3 "2008-06-05T23:45:56Z")
No, I have a complete off the shelf AC motor controller which uses SCR’s (or maybe IGBTs?) I want to disconnect the “switchers” in the drive, and connect bigger ones external to the drive. Something like this… ![](http://www.ctr-surplus.com/michelle/21618-2.jpg) IGBT is Rated 300A at 1200V. Could the firing circuit designed for a 2 hp system be made to fire these IGBTs? ---
**Author:** ![Seafarer12](https://avatars.discourse-cdn.com/v4/letter/s/e56c9b/32.png) [@Seafarer12](https://community.electricforum.com/u/Seafarer12)\ **Post date:** [June 6, 2008, 3:03pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/4 "2008-06-06T15:03:34Z")
SCR’s are use in soft starters. As far as using the brains to fire larger IGBT’s or something. It may or may not work depending on the drive. The problem would be you would have no over current protection or way to monitor it like you do on a regular drive. If you could figure out how it senses current you might beable to scale it to your needs. Too bat it just doesn’t have CT’s. As far as it driving your a/c it should work fine if you want to use an AC motor to run your a/c ---
**Author:** ![Sir\_Joab](https://avatars.discourse-cdn.com/v4/letter/s/7bcc69/32.png) [@Sir\_Joab](https://community.electricforum.com/u/Sir_Joab)\ **Post date:** [June 6, 2008, 8:26pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/5 "2008-06-06T20:26:03Z")
IGBTs would work great, just make sure you don’t drive the Gate more than 20V above the Emitter, and not less than 20V below the Emitter. This will cause the Gate to weld to the Emitter, and then the component turns into smoke. ---
**Author:** ![ElectriCar](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@ElectriCar](https://community.electricforum.com/u/ElectriCar)\ **Post date:** [June 10, 2008, 7:37pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/6 "2008-06-10T19:37:09Z")
Newb here. Etis, the photo you show is not an SCR. That is a transistor of some type, which is used to switch the power from the DC buss off and on to create an AC waveform. SCR’s are used in DC drives, which make DC from an AC source by rectifying 0-100% of the positive or negative half of the sign wave. They turn off when the sign wave reverses polarity, reversing the polarity on the device. I’ve worked on SSD drives before. Ours had MOV’s for protection which frequently blew on our drives. RE changing the xistors to larger ones, that would be a question for SSD tech support. They may fit in there and may work ok but the drive controls may not. You wouldn’t want to buy them only to have them not work or the drive not function properly. ---
**Author:** ![Sir\_Joab](https://avatars.discourse-cdn.com/v4/letter/s/7bcc69/32.png) [@Sir\_Joab](https://community.electricforum.com/u/Sir_Joab)\ **Post date:** [June 10, 2008, 9:17pm UTC](https://community.electricforum.com/t/ac-drive-scr-swap/716/7 "2008-06-10T21:17:33Z")
[QUOTE=ElectriCar;3136]Newb here. Etis, the photo you show is not an SCR.[/QUOTE] It’s an IGBT.