I'm reviving a dummy load project that I started a few years ago, but was delayed by the high cost of the switch. Originally I came up with a 4 pole switch, but I think it can be done with a 3 pole switch.
I'd like to have it be 3 position, 4, 8 and 16 ohm.
Who makes a switch with this logic?
I'd like to have it be 3 position, 4, 8 and 16 ohm.
Who makes a switch with this logic?
The switch would also have to be a "break-before-make" type.
Otherwise, a potential problem with your circuit is that if you are in the 4-ohm position, and then you switch to the 8-ohm position, and SW3 closes before SW1 or SW2 opens there will be a momentary short circuit.
Same thing happens when going the other way too.
Some amps may not like this if the switch is operated while the amp is being driven.
I built a dummy load with no switch - just two binding posts for each resistor and configure it with stacking banana plug jumpers.
Otherwise, a potential problem with your circuit is that if you are in the 4-ohm position, and then you switch to the 8-ohm position, and SW3 closes before SW1 or SW2 opens there will be a momentary short circuit.
Same thing happens when going the other way too.
Some amps may not like this if the switch is operated while the amp is being driven.
I built a dummy load with no switch - just two binding posts for each resistor and configure it with stacking banana plug jumpers.
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I realized that I could do it with three switches, but I wanted to make this new load more "idiot-proof" as I fade off, mentally into the sunset. LOL
My current load only does 8 & 4 ohms.
I've got most of the parts to build the new load, but that switch is a tough one to find.
My current load only does 8 & 4 ohms.
I've got most of the parts to build the new load, but that switch is a tough one to find.
Here's what I did with four 100 Watt 8 ohm resistors to get:
1) 2 Ohm - one channel @ 400W
2) 4 Ohm - two channels @ 200W each
3) 8 Ohm - four channels @ 100w each
4) 16 Ohm - two channels @ 200W each
There are other combo's but these are enough fro me.
Lately I've been building multi channel amps and having a load with four identical channels has been great.
1) 2 Ohm - one channel @ 400W
2) 4 Ohm - two channels @ 200W each
3) 8 Ohm - four channels @ 100w each
4) 16 Ohm - two channels @ 200W each
There are other combo's but these are enough fro me.
Lately I've been building multi channel amps and having a load with four identical channels has been great.
Attachments
Attachments
If you don't mind using a rotary switch, this one will do the trick.
4 Position Rotary Changeover Switch
Some amps might take revenge on the switch!
Seriously, isn't switching a big load of DC a big torture test for a switch? Since you know one day a teenager will come along...
Use relays or contactors with a DC rating twice that you expect.
They will be durable.
And less easy to mess up.
Be aware that some switches are 15A AC / 3A DC, DC needs a really beefy switch...
They will be durable.
And less easy to mess up.
Be aware that some switches are 15A AC / 3A DC, DC needs a really beefy switch...
That rotary could work. The only possible challenge is the depth. I have about 3/4" of space between the aluminum plate and the heatsink itself. But that is a good possibility.
Relays are out because there is no power source.
Relays are out because there is no power source.
On closer look, I need a logic table where two contacts are closed in one of the positions, so that switch on Amazon won't work.
Sorry give you the wrong link, this is the correct one:
20A Rotary Changeover Switch 660V 4 Position 3 Phase 12 Terminals
20A Rotary Changeover Switch 660V 4 Position 3 Phase 12 Terminals
Yup, that's more like it. I can use the double sets of contacts for the state where I need to close two at once. This looks flexible. Thanks!
I found a DPDT ON-ON-ON toggle switch option, but the toggle switch rated 15A and cost 4 times higher than the rotary cam switch.
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When I traced the schematic in post 1, I believe there was a typo, it should be SW1 and SW3 closed = 4 ohm.
And I found that SW1, SW2 & SW3 can be simplified to two SPDT switch and came out with a new schematic uses a 3 position DPDT ON-ON-ON toggle switch instead.
At center position, SW1 stay down, SW2 moves to up position, only one of 8ohm resistor to complete the circuit (= 8ohm).
And I found that SW1, SW2 & SW3 can be simplified to two SPDT switch and came out with a new schematic uses a 3 position DPDT ON-ON-ON toggle switch instead.
At center position, SW1 stay down, SW2 moves to up position, only one of 8ohm resistor to complete the circuit (= 8ohm).