Switching high voltage high amperage loads

[sylathnie]

Well I have my batteries. My Bulbs and my Ele 2. Now I need to figure out how to switch this thing on and off. 11 Amps is the limit for my current Frankenswitch (My house smells like I've been racing slot cars from all the arcing of my various switch experiments.)

I need to swith about 29V and 14A or so on and off. I don't have any problems soldering or manufacturing. I would hope for something that doesn't require a specially machined housing but if someone can make one please chime in.

Any thoughts?

 

[TigerhawkT3]

I have a pair of 12V 50A rated toggle switches for my LK12 (one is inside the body to act as a safety), and they've been handling 28V 20A (30A at startup) just fine. I got them from Kragen (auto parts shop). For your slightly lower current, you might be able to find a relay of reasonable size and cost.

 

[Al Combs]

Well I have my batteries. My Bulbs and my Ele 2. Now I need to figure out how to switch this thing on and off. 11 Amps is the limit for my current Frankenswitch (My house smells like I've been racing slot cars from all the arcing of my various switch experiments.)

I need to swith about 29V and 14A or so on and off. I don't have any problems soldering or manufacturing. I would hope for something that doesn't require a specially machined housing but if someone can make one please chime in.

Any thoughts?

What about using a MOSFET? The CPF link mentions one for up to 30 volts. The link for IRLR7843 is just below the first large picture. The spec sheet says it handles up to 30 amps. Sorry I don't know a lot about electronics myself. It looks fairly simple. It also looks like it should work. Maybe one of the electronics guys can chime in.

 

[sylathnie]

Thanks! That was the exact link I needed. I just finished building my switch. Everything seems to be working fine.

 

[Der Wichtel]

you will need a voltage divider because 29V are too high for the gate-source voltage of the IRLR7843

 

[Al Combs]

you will need a voltage divider because 29V are too high for the gate-source voltage of the IRLR7843

If he used the simple resistor bridge petrev shows in the first picture of his article, it should work fine.

 

[Der Wichtel]

If he used the simple resistor bridge petrev shows in the first picture of his article, it should work fine.

oops, didn't click on the link you posted because I thought that was the link to the mosfet.

Yes, the two resistors act as a voltage divider

 

[Al Combs]

Thanks! That was the exact link I needed. I just finished building my switch. Everything seems to be working fine.

Glad to hear it!

 

[Al Combs]

Der Wichtel, I was looking at the buck regulator in your sigline. Is that a constant current regulator, or a voltage regulator? Sorry, I couldn't really tell. I'm just curious for my own Mag3D-P7. I never did find a proper regulator for it. I did a little looking around and found quite a few high efficiency switching type voltage regulators that can handle the power. But so far I haven't seen any that can output 3 amps as a constant current regulator.

The best voltage regulator I saw only goes down to 0.9 volts. So if you wanted to rig a constant current regulator from that, the sense resistor you wire in series would draw about 25% of the total power. Almost a 3 watts loss in the resistor, no matter how efficient the regulator is.

Going the other way, is a voltage regulator good enough? SSC's P7 PDF doesn't have a graph of dropping forward voltage as junction temps rise. But there is one on page 13 of the P4 PDF. The pure white emitter drops about 1/4 volt for a rise from 25°C to about 140°C. If it's valid to compare P4's and P7's, page 4 of the P7 PDF says 3.6 volts=700 lumens and 3.3 volts=400 lumens. Almost the same voltage spread as the possible range of forward voltage variation.

If there ever was a thermal runaway, a voltage regulator would just dump in more power and blow the LED. That was why I gave up on the idea.:sigh:

 

[sylathnie]

I actually ended up using the IRF 2804 that was part of the charging board of my Ryobi pack. I took a look at the spec sheet and I think it will fit my needs perfectly.

 

[Al Combs]

I actually ended up using the IRF 2804 that was part of the charging board of my Ryobi pack. I took a look at the spec sheet and I think it will fit my needs perfectly.

It's always nice when the stuff you need, you already have around the house.

 

[SafetyBob]

This thread really brings up the point that we need to convince JimmyM to make another batch of his switch he made using an FET.

I was about ready to start doing my final research into FET's, because when I first read about JimmyM's first builds using FET's I was still into those LED lights. Then I build my first M@g85. I don't think I need to say more.

I could really use a nice switch. OK, I already have AW's beautiful multilevel switch, but I would like a nice single level switch too for those huge, big lights.

What does everyone else think? Don't we really need a proper switch for these higher wattage builds?

Bob E.