Author Topic: Another Dummy Load Project!  (Read 13319 times)

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Offline ZachFlem

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Re: Another Dummy Load Project!
« Reply #50 on: July 05, 2012, 06:48:46 am »
Smallest I have seen were OEM for Toyota and Ford. most were used for headlight switches, and they are half the width of the standard 30A automotive relay. Most automobile relays either have a built in diode ( actually 2 so that it will only work one way round) or have a resistor across the coil to attenuate the pulse. Nothing else is needed for use with a switch.

I think you misunderstand where I want to put the diode.

I was thinking of using these (http://bit.ly/MW9t5V or similar)

with the DC input going into the relay on pin 30.
the load output on pin 87
pin 86 goes to earth
and pin 85 recieves 12vdc from my switch.

assuming the switch goes up in 10a steps, so relay 1 = 10a, relay 2 = 20a etc, could i not put a 6a diode between the load output (pin 87) and the switch input (pin 85) so that when the 20a relay is activated by the switch, the diode back feeds power to any previous relays?

I'm assuming that the switch contacts of the relay aren't going to draw any more power then they need and that the 6a diode will be enough.

Unless someone can point me in the direction of a rotary switch that step and hold the previous step... if you know what I mean!

the other option, is to simply use 20a 12vdc rocker switches and forget the relays all together...
 

Offline codeboy2k

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Re: Another Dummy Load Project!
« Reply #51 on: July 05, 2012, 09:46:00 am »
Zach, your idea can work, with the load side switch back-feeding the previous relay coil. I don't like it because my preference
would always be to keep the control and the load separate. Your idea would be implemented better if your relay had a second
pole and contact, basically a double-pole, double-throw switch or a double-pole, single-throw switch. Then you can feed the
previous relay from a contact on the next relay, and you don't even need a diode then.

Here is an example circuit with diodes on the rotary switch.  As you switch up to the next level, the diode feeds power to
the previous level. The downside is that each new level adds a diode drop, so you should use Schottky diodes to minimize
the drop, and secondly, each higher level has to supply all the current to itself and all the relays of the previous levels. So
the diodes have to have enough DC current and power handling capability for all the relays before it. The worst case is the last
diode, which has to power all the relays.


 
 

Offline ZachFlem

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Re: Another Dummy Load Project!
« Reply #52 on: July 05, 2012, 10:47:20 pm »
assuming i use the Narva relays mentioned earlier, with their current draw of 0.15a @ 12vdc, I can't see why a 6a diode wouldn't be more than enough, my reasoning says that at 6a, it's 4 times the capacity of my 10 relays (1.5a in total) and should be more then enough.

I'm also considering going down the individual switch route, as it will reduce the overall cost of the unit considerably...
 

Offline codeboy2k

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Re: Another Dummy Load Project!
« Reply #53 on: July 06, 2012, 01:33:58 am »
assuming i use the Narva relays mentioned earlier, with their current draw of 0.15a @ 12vdc, I can't see why a 6a diode wouldn't be more than enough, my reasoning says that at 6a, it's 4 times the capacity of my 10 relays (1.5a in total) and should be more then enough.

exactly. Using 6A diodes is more than enough. 3A diodes would suffice with your 150mA relay coils.

Quote
I'm also considering going down the individual switch route, as it will reduce the overall cost of the unit considerably...

simple too. :)
 


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