I want to use a DPDT relay to switch my positive and negative voltage rail on or off. If my rails are at +/- 25V and the relay is rated for DC 30V, does that work? Or would I need a relay rated for more than 50V? One relay leg is switching +25 and the other -25V, but I'm not sure if that's considered less than 30V, or more. Thanks.
What is the Amps rating of the relay and the load?
I stick to a 2x factor of safety for volts and 3x for Amps, for DC loads, the break rating is important.
For a 25V load, I would prefer a higher voltage capable relay than 30V.
There are many choices sold, from many makers, find one that can replace the existing relay.
Or go for chassis mount, again choices abound.
I stick to a 2x factor of safety for volts and 3x for Amps, for DC loads, the break rating is important.
For a 25V load, I would prefer a higher voltage capable relay than 30V.
There are many choices sold, from many makers, find one that can replace the existing relay.
Or go for chassis mount, again choices abound.
I'm going to say no, its not high enough rated. The problem is that the contacts will probably not break and make the two rails simultaneously, one may be a millisecond or two ahead or behind the other. That means that the last relay to close sees 50 volts across it due to the circuitry all floating up to the voltage of the contact that was first to close.
Unless you have an absolutely pressing need to switch the DC rails it is far better (imo) to switch the AC feed to the supply.
Depending on the currents involved solid state switching could be viable.
Some information about relays and in particular the difficulties and dangers of switching DC:
http://sound-au.com/articles/relays2.htm
http://sound-au.com/articles/relays2.htm
Big thing to worry about when mechanically switching DC is that if the source has a large cap on its output and the load has a sizable capacitance on its input, a large current transient could weld the contacts of the relay together, or, if not that, severely shorten contact life due to arcing.
I'm trying to derive several other power supplies from the main toroid, so I can't switch it off entirely. So next best solution is to kill the rails, and the channel amplifiers, when they aren't in use.
Hey Tom, any recommendations for a part that might work? This is a new area for me. I've seen lots of circuits to switch a positive rail, less so for a negative one. I'm looking to switch both using a 3V3 or 5V control voltage. I'll browse Mouser in the meantime. Thanks.
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I'm sure Tom will have some good suggestion on FET's.
This is something I had from ages ago that shows the idea and how simple it can be. It is not meant as a definitive circuit, just a way to show how it is done. There are FET's available now with really low on resistance which is ideal for rail switching.
The upper FET is an IRF9640 which isn't one of the lowest resistance FET's around but the lower FET was an IRF2907 which is much better (and there are better than this around). Load current here is about 2.3 amps.
Switch on:
And switch off:
This is something I had from ages ago that shows the idea and how simple it can be. It is not meant as a definitive circuit, just a way to show how it is done. There are FET's available now with really low on resistance which is ideal for rail switching.
The upper FET is an IRF9640 which isn't one of the lowest resistance FET's around but the lower FET was an IRF2907 which is much better (and there are better than this around). Load current here is about 2.3 amps.
Switch on:
And switch off:
Can these be used?
DC to DC Input 3-32VDC Output 5-200VDC 25A Single Phase Semi-Conductor Relay Module
Two for $14usd!
DC to DC Input 3-32VDC Output 5-200VDC 25A Single Phase Semi-Conductor Relay Module
Two for $14usd!
One toroid feeding umpteen supplies?
Use separate rectifiers for each supply & switch the AC secondary from each channel, then you are switching AC not DC.
I also have a zener in series with relay coil flyback diode.
It makes relay release quicker and so less arcing.
No. Without knowing what amp you're powering I can't make any recommendations.
You need to find a power MOS that'll handle the current, voltage, and has a low on resistance. It shouldn't be a big deal to find a 100 V MOSFET that'll suit your needs.
Tom
Can you please chk my rough diagram for correct orientation and mention values for Zener , say for 5V , 12V, 24V relays assuming 1N4007 flyback diode.
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Will switching secondary side AC using a relay reduce these problems?
Use of Triac 8T44HA /Diac DB3 used in fan regulators, is it a good or bad idea in an audio amp?
Using the same toroid for different circuits in a small space...is experimental.
Partly loaded transformers do not give good performance, and here in India, we prefer E-I designs for such variable loads, toroids have a narrower sweet spot for use.
Best is use separate supplies, or AC switches on secondary side, before rectifier, as suggested above.
Overall, not a wise decision.
There are typical circuits for the triac mentioned, and the BT131 / 136 / 139 are commonly seen in fan regulators, and some fans exhibit humming and cogging, so I would hesitate to use such a device in audio amplifiers.
Best use a solid state relay, many choices exist...they use a thyristor, not a triac, mostly with opto-coupler and smoothing circuits, with high isolation between control and mains circuits.
Of course, a two pole contactor or relay will work nicely, simple and reliable.
Partly loaded transformers do not give good performance, and here in India, we prefer E-I designs for such variable loads, toroids have a narrower sweet spot for use.
Best is use separate supplies, or AC switches on secondary side, before rectifier, as suggested above.
Overall, not a wise decision.
There are typical circuits for the triac mentioned, and the BT131 / 136 / 139 are commonly seen in fan regulators, and some fans exhibit humming and cogging, so I would hesitate to use such a device in audio amplifiers.
Best use a solid state relay, many choices exist...they use a thyristor, not a triac, mostly with opto-coupler and smoothing circuits, with high isolation between control and mains circuits.
Of course, a two pole contactor or relay will work nicely, simple and reliable.
Humming noises are inaudible at high speeds as the Triac drop is minimal, I don't know if that can create problems in audio (like interference in AM radio ). But SSR may have lower noise , since its a dedicated device