Hi all
I am new to the website but not a total newbie 🙂
I have designed and built a powerfull class A/AB amp with a fat 900VA toroidal transformer and 80mF cap bank. Works well. I use a soft starter as well that works based upon temperature dep resistors and a relay, etc.
Now I am implementing a standby system using Arduino and another relay. It turns off the relay 20 min after trigger voltage is out.
My question is this : is it alright to put the standby relays (two channels for dual power per audio channel) in between the transformer and the cap bank? The relay is rated 30VDC and 250VAC and the voltage is 35VAC. So no issues in terms of AC voltage. Thr issue is in-rush current. Would the cap bank have a large in rush current and burn the elay contacts? Or this is mainly an issue with the xformer which is anyway being taken care of by the soft starter?
I understand the in rush current of the caps depend on the capacitance and ESR but I don't know the ESR values for the cheapo caps which work by the way.
Another easy way is to put the relay on the mains before the soft starter. But then I need an extra xformer to power up my controls.
Thanks in advance for any insights by tbe DIY masters 🙂
Arta
I am new to the website but not a total newbie 🙂
I have designed and built a powerfull class A/AB amp with a fat 900VA toroidal transformer and 80mF cap bank. Works well. I use a soft starter as well that works based upon temperature dep resistors and a relay, etc.
Now I am implementing a standby system using Arduino and another relay. It turns off the relay 20 min after trigger voltage is out.
My question is this : is it alright to put the standby relays (two channels for dual power per audio channel) in between the transformer and the cap bank? The relay is rated 30VDC and 250VAC and the voltage is 35VAC. So no issues in terms of AC voltage. Thr issue is in-rush current. Would the cap bank have a large in rush current and burn the elay contacts? Or this is mainly an issue with the xformer which is anyway being taken care of by the soft starter?
I understand the in rush current of the caps depend on the capacitance and ESR but I don't know the ESR values for the cheapo caps which work by the way.
Another easy way is to put the relay on the mains before the soft starter. But then I need an extra xformer to power up my controls.
Thanks in advance for any insights by tbe DIY masters 🙂
Arta
Welcome to diyAudio 🙂
I think relays and switching the secondaries are going to be a non starter given your 80mF reservoir caps. The caps will appear as 'almost' a short when initially connected. The ESR will be very low whether you are using a few parallel 10mF caps or a zillions of 1mF caps in parallel.
Switching the primary is always the way to go generally.
One idea (and one I use) is to use a relay with a mains voltage coil and trigger the relay with an opto isolated triac. That would need only a low voltage trigger input to the switching circuit and it would be totally isolated from the mains.
I actually use a on opto cable to trigger mine with the relay switching circuit having a 3.6v nicad backup supply and a CMOS timer circuit. It is used to turn all the source components on when the amp is powered up.
Going back to your original idea... solid state relays could be workable as they are optically isolated with each using a photo voltaic coupler. Each relay would need two power FET's of appropriate rating (high current and low on resistance). These are used a lot as speaker relays and work really well. That could be workable.
I think relays and switching the secondaries are going to be a non starter given your 80mF reservoir caps. The caps will appear as 'almost' a short when initially connected. The ESR will be very low whether you are using a few parallel 10mF caps or a zillions of 1mF caps in parallel.
Switching the primary is always the way to go generally.
One idea (and one I use) is to use a relay with a mains voltage coil and trigger the relay with an opto isolated triac. That would need only a low voltage trigger input to the switching circuit and it would be totally isolated from the mains.
I actually use a on opto cable to trigger mine with the relay switching circuit having a 3.6v nicad backup supply and a CMOS timer circuit. It is used to turn all the source components on when the amp is powered up.
Going back to your original idea... solid state relays could be workable as they are optically isolated with each using a photo voltaic coupler. Each relay would need two power FET's of appropriate rating (high current and low on resistance). These are used a lot as speaker relays and work really well. That could be workable.
Hi Arta,
I would switch the primary instead of the secundary. Make the fuse as small as allowed for full power and switching on.
Regards. Gerrit
I would switch the primary instead of the secundary. Make the fuse as small as allowed for full power and switching on.
Regards. Gerrit
Thanks lads for the suggestions!.
I purchased a small 12-0-12 toroid then to power my controls and will put the relay on the primary with 5A 230V fuse. I will also use an optocoupler in conjunction with the little Arduino which I use for both overheat protection as well as triggering.
Cheers
Arta
I purchased a small 12-0-12 toroid then to power my controls and will put the relay on the primary with 5A 230V fuse. I will also use an optocoupler in conjunction with the little Arduino which I use for both overheat protection as well as triggering.
Cheers
Arta
Guys
Many thanks again. Just an update: I ended up putting a small additional toroid to power up my control Arduino. The whole thing is now assembled and spounds ballistic. It is a KSA50 topology. I enclosed a photo.
I need a pair of good sppeaker. Currently using a pair of small oldish KEF.
Arta
Many thanks again. Just an update: I ended up putting a small additional toroid to power up my control Arduino. The whole thing is now assembled and spounds ballistic. It is a KSA50 topology. I enclosed a photo.
I need a pair of good sppeaker. Currently using a pair of small oldish KEF.
Arta
Looks awesome, I like very much the plaited wires.
However I did spot something:
If you have 35Vac from each secondary, that gives you a 35 x Sqrt(2) = 50Vdc (about, mains voltages vary) line voltage.
But I see your audio amps have 3300uF 50V parts on there!
Personally I would change them up to 63V parts, as I've seen old caps struggle with their rated voltage (even Nichicon) and start leaking. Not sure what the big banks of caps are either, but anything on that 50Vdc rail I would spec at least 63V, and small caps can be 100V or more, as space permits.
If you decide to order new caps - make sure they'll fit first, dimensions look tight.
Consider bypassing the amplifier caps with some decent 63V+ film caps, 2.2uF perhaps, if not already.
The next mod might be to isolate the driver section PSU and output transistors so voltage sags do not impact the driver - a careful scope probe on the power rail while playing music would reveal what's on there... I run two bridge+caps PCBs on the same transformer to do that (smallish caps for the driver, bigger cap bank for the output transistors). I.e. like you have done already for each channel, but add 2 smaller boards for the driver sections and hack the tracks on the amp PCB to isolate them.
But that's just my ideas LOL, take no notice, depends what the goal is 😀.
However I did spot something:
If you have 35Vac from each secondary, that gives you a 35 x Sqrt(2) = 50Vdc (about, mains voltages vary) line voltage.
But I see your audio amps have 3300uF 50V parts on there!
Personally I would change them up to 63V parts, as I've seen old caps struggle with their rated voltage (even Nichicon) and start leaking. Not sure what the big banks of caps are either, but anything on that 50Vdc rail I would spec at least 63V, and small caps can be 100V or more, as space permits.
If you decide to order new caps - make sure they'll fit first, dimensions look tight.
Consider bypassing the amplifier caps with some decent 63V+ film caps, 2.2uF perhaps, if not already.
The next mod might be to isolate the driver section PSU and output transistors so voltage sags do not impact the driver - a careful scope probe on the power rail while playing music would reveal what's on there... I run two bridge+caps PCBs on the same transformer to do that (smallish caps for the driver, bigger cap bank for the output transistors). I.e. like you have done already for each channel, but add 2 smaller boards for the driver sections and hack the tracks on the amp PCB to isolate them.
But that's just my ideas LOL, take no notice, depends what the goal is 😀.
@Globulator
Apologies for getting back to you so late. Somehow your reply went unseen, embarrassing really! I very much appreciate your suggestions. The good thing is that I can now give you some feedback after using the amp for over a year. It has been fantastic - phenomenal I would say. I got a pair of very nice speakers and have not been happier really.
The rail voltage is 35VDC, sorry for the typo. I will add the bypass caps, somehow I remember I had few 100s of nF but need to check.
Re your suggestion on isolating the driver section PSU and output transistor, I am going to do some research to make sure I understand your point fully.
Thanks again
Arta
Apologies for getting back to you so late. Somehow your reply went unseen, embarrassing really! I very much appreciate your suggestions. The good thing is that I can now give you some feedback after using the amp for over a year. It has been fantastic - phenomenal I would say. I got a pair of very nice speakers and have not been happier really.
The rail voltage is 35VDC, sorry for the typo. I will add the bypass caps, somehow I remember I had few 100s of nF but need to check.
Re your suggestion on isolating the driver section PSU and output transistor, I am going to do some research to make sure I understand your point fully.
Thanks again
Arta