I've been experimenting with an ACS712 and solid state relay in place of rail fuses. It works, but gets expensive fast when doing stereo or multi-channel. Sensing current off the main transformer sounds like a neat idea, but is only useful for monoblock designs. I haven't had time to look into other options yet, but this is something I plan to do in the future.
How much current does this thing draw?
I'm thinking of buying a dual secondary 12v transformer to power two boards.
Will this one be big enough?
Toroidal Transformer 30VA 2 x 12VAC Output Supplied with Mounting Kit UK Seller | eBay
I'm thinking of buying a dual secondary 12v transformer to power two boards.
Will this one be big enough?
Toroidal Transformer 30VA 2 x 12VAC Output Supplied with Mounting Kit UK Seller | eBay
That should work great. You can use one output winding for each board.
The bulk of the current draw in these is the relays. You won't be using a tube relay. The power and inrush relays are only both active for half a second, and your speaker relays are solid state which draw the same as an LED, so total draw will likely be under 250mA worst case.
The bulk of the current draw in these is the relays. You won't be using a tube relay. The power and inrush relays are only both active for half a second, and your speaker relays are solid state which draw the same as an LED, so total draw will likely be under 250mA worst case.
your 30VA 12+12Vac transformer has a maximum continuous AC current of 1.25Aac
When feeding a capacitor input filter the maximum continuous DC current drops to about half, i.e. 612mAdc
If you want the transformer to run cool, then reduce your CONTINUOUS DC current to ~300mAdc.
That's a lot of continuous current to play with. Especially with 24V relays often drawing around 10 to 15mAdc, without a current reducing circuit.
When feeding a capacitor input filter the maximum continuous DC current drops to about half, i.e. 612mAdc
If you want the transformer to run cool, then reduce your CONTINUOUS DC current to ~300mAdc.
That's a lot of continuous current to play with. Especially with 24V relays often drawing around 10 to 15mAdc, without a current reducing circuit.
My transformer math works out the same as yours, but this uses 12V relays and the suggested relays draws 138mA through their coils, so that transformer is perfectly sized.
G7L-1A-BUBJ-CB-DC12 Omron Electronics | Mouser
G7L-1A-BUBJ-CB-DC12 Omron Electronics | Mouser
They are high power relays.
1.9W through the coil, cf. small relays that are around 200 to 400mW.
A power saving circuit would be a good idea.
What voltage do they drop out at?
Will they hold in reliably at 50% current?
We have a pumped domestic water supply. The pumps are controlled with mains relays.
The one major failing was a relay coil burning out due to high dissipation in the coil. It was always the same relay. The householder that looked after the maintenance/service contractor suggested a different make of relay. Problem solved. The contractor did not even think about a solution to prevent breakdowns.
1.9W through the coil, cf. small relays that are around 200 to 400mW.
A power saving circuit would be a good idea.
What voltage do they drop out at?
Will they hold in reliably at 50% current?
We have a pumped domestic water supply. The pumps are controlled with mains relays.
The one major failing was a relay coil burning out due to high dissipation in the coil. It was always the same relay. The householder that looked after the maintenance/service contractor suggested a different make of relay. Problem solved. The contractor did not even think about a solution to prevent breakdowns.
I actually burned a transformer up in my initial testing with these relays. This was the reason why we changed the software to shut off the inrush relay once the power relay energized. In my builds I use lower coil current relays.
I plan to explore controlling a power relay module over an I2C bus. This would make controlling dual monoblock designs much easier from a single control board. A power saving circuit would only require an extra resistor and some software modification to make it work.
I plan to explore controlling a power relay module over an I2C bus. This would make controlling dual monoblock designs much easier from a single control board. A power saving circuit would only require an extra resistor and some software modification to make it work.
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Hi Jeff,
Today I tried to test the board with my little relay boards attached. I hooked up a +-36V SMPS to the power sense. The board runs through the sequence just as you described but after the speaker protect relays switch on then the whole thing shuts down and the LED blinks slowly. Are there any terminals that need to be shorted during testing?
Thanks, Terry
The board should operate without anything jumpered. 1 blink every two seconds means it's detecting a voltage loss in the 12V supply. Pin D9 on the Arduino should be Low. Q9 should pull it low. The base of 9 gets current right from the 12V transformer. D3 rectifies it. If it's not flowing enough current, you may need to increase C1.
Well, sometime after midnight I figured this out.....
Board #1 had a poorly soldered micro USB port
Answered my own question when I specified the PL-2303HX serial chip
Downloaded the Prolific serial driver for this chip and it worked.
I guess all this chinese stuff could have anything installed on the serial so each board should be checked.
Jeff
Are these the new boards suited for tube amps you mentioned in a PM to me a couple weeks ago?
Any inputs for monitoring a voltage divider on the A0-A5 terminals?
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