Using a transformer to run a 96v brake  

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(@jeppe240)
Member
Hi!
Im looking to build a hubdyno, and i have found (not yet bought) a retarder but the problem is the the retarder only has 8 12v coils (96v) so i have to convert the the voltage from 230v (our standard voltage) to 115v but from what i have read mixing a transformer and phase angel control isnt so good because of "harmonic emissions"?

So i wonder if i can use/make some sort of filter to make the circuit work, or if it isnt needed at all and the transformer
can handle it?
Or should i just keep looking for a retarder that can be run on 192v and skip the transformer?

Regards Jesper

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Posted : 15/08/2019 6:12 pm
(@trinom)
Member Customer

I'm solving exactly the same task with my water cooled eddy current engine dyno (96V, 2A). I decided to build my own driver with constant current output, so no PWM. I don't know, if you are in a hurry, or you can just wait for my solution...

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Posted : 16/08/2019 10:00 pm
(@admin)
Member Admin

Hi,

Lots of dynos run on 96V. The SportDevices brake supply supports it without a problem. You can also use other supplies, just know the current is a spiky with the switches (thyristors or similar) on maximum 50% of the time. So at max power, the current is twice the rated current for 50% of the time, so choose components to support this. A 220V-110V transformer lowers the max current, but the average current is the same. 

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Posted : 25/08/2019 5:52 pm
(@trinom)
Member Customer

"110V transformer lowers the max current" ... Are you sure? Why would it do that? It lowers the voltage to 1/2 and potentially doubles the current, if it's made as beefy as it should be.

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Posted : 26/08/2019 9:03 pm
(@admin)
Member Admin

Hi, yes the average current is set by the brake and the voltage, it is the same in any configuration. But if you use 220V AC to create 0-96V DC, then the switches that draw current from the AC will never be on more than about half the time. So in that time the current will be roughly double. 

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Posted : 26/08/2019 9:18 pm
(@trinom)
Member Customer

It looks like we are both talking about different things. I was talking about normal transformer and you are talking about switch mode power supply, right?

Also the brake can be considered an ohmic load, if you drive it in a constant current mode. In that case it's also true, that with decreasing voltage the current decreases as well.

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Posted : 27/08/2019 6:17 am
(@mach_1)
Member
Posted by: Tomas Tryska

It looks like we are both talking about different things. I was talking about normal transformer and you are talking about switch mode power supply, right?

Also the brake can be considered an ohmic load, if you drive it in a constant current mode. In that case it's also true, that with decreasing voltage the current decreases as well.


Please explain ? Or is it a secret, or can you divulge more information ?

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Posted : 27/08/2019 11:47 am
(@trinom)
Member Customer

There's no secret. I just don't want to feed the brake with PWM signal.

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Posted : 30/08/2019 3:00 pm
(@mach_1)
Member
Posted by: Tomas Tryska

There's no secret. I just don't want to feed the brake with PWM signal.

That part I understood already! "if you drive it in a constant current mode. "

Going to be physically one big transformer!

 

 

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Posted : 30/08/2019 11:29 pm
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