I suggest you use a IRF3205 55V-110A-8mohm. Applying 12V in its gate with a transistor or a CMOS is enough to switch.

Cilmo.

I would use the control signal to pull in a contactor rated for your application. Might even use a vacuum contactor.

The IRF3205 looks promising.

Do you have an example of this contactor or vacumm contactor.

We are trying to avoild using a solenoid relay due to noise concerns.

I'll design a circuit and send to you, but first tell me the operating frequence this circuit will work.

Cilmo.

How "High temp" is high temp?? You might want to check that spec for the 3205.

Bill

At least 85°C.

I suggest you use a IRF3205 55V-110A-8mohm. Applying 12V in its gate with a transistor or a CMOS is enough to switch.

Cilmo.

How about a Crydom D1D40L, rated 40 A @ 100 VDC. You may need to use a heatsink with any solid state relay, 'cause they do dissipate heat. The D1D40L dissipates about 18 W at 20 A. Datasheet is here.

Looks like you'll need a heatsink rated at 2^oC/W at 18 W up to about 60^oC ambient T.

Electro mechanical DC contactors for 50 amps with ac/dc coils are available from reputed manufacturers like ABB,Siemens,telemechaniq.You can try .But you have to check the no of switching per minute, while selecting the contactor

You might also look at a mercury displacement relay.

"\I currently have a Nason 30A pneumatically activated relay (pressure switch).\"

Use 2 in parallel? 60 A rated!

No, please, no!

First, you should synchronize the two switches, then you should symmetrize the currets...

Not advisable.Switching of both will not take place at the same time.There will be difference in milliseconds which will affect the system.

No. Don't do this: it is impossible to ensure that both will break exactly at the same time; one of them will switch at 0A and the other at 50A, which is over the top of the 30A rating.

Yes, there is a moment of single operation, but he is already using only one of the devices and his failure complaint is heat buildup not surge capacity!

I give this idea as a way to easily enhance this situation, heat build up from continuous current draw.

And by the way if you wish to do this the expensive engineering way use IGBT's with voltage regulated control circuit. 3205 mosfets come in a to220 case and HEAT dissapation, the original complaint, will come into play. With the IGBT's you can make a highly stable solid state relay with plenty of dissapation.

Sorry electrical engineering guys, I am used to working on a budget out of my own pocket, not out of my employer's wallet.

<he is already using only one of the devices and his failure complaint is heat buildup not surge capacity>

Point taken, though the poster's suggested setup is not to be recommended, simply because the device is already operating at 160% of its rated, tested capacity. It might be OK. It might fail early. This situation is outside the original equipment manufacturer's comfort zone, and the poster needs to be aware that (s)he is in 'uncharted waters'.

Well spoken. It would be working outside the box and not according to spec.

As to the 3205, it is a commonly used in my field of mobile electronics, it is very durable if used with switching duty cycle for cooling time. But it has only 200w of heat dissapation via the to220ab case style. Drawing 50amps continuously at 12volts will far exceed the heat dissapation of this device by three times, and you are starting at 85 degrees not 0. Removing the switch to a cooler spot would help, but still will not work.

This device may work within parameters. I only glanced at some of them, so I could be wrong. Which I am prone to be. IRGPS60B120KD

Try this for cheap DC contactors

www.albright.co.uk

Thanks for all the feedback. I should add a bit more information on the application.

I do not want to used coil contactors due to noise issues.

Currently I have 30A SPDT pneumatically activated switches. They are part of a measurement system and both the positive and negative leads have to be switched.

In the off positive they connect a charger to the battery which supplies the current.

In the alternate (measuement) position they apply the current across electrodes immersed in a liquid.

This is a high temperature application and SSRs have failed in the shorted state when we tried 30A version.

There are lots of MOSFET or IGBT selected with regard to your specification.

low voltage can be up to 60 and 100v. 50,60,100A enough.

besides, as 12x50=600w/110v (220)=~6A (3), so another plan can be adopted by selecting a small contactor to control input termianl.

many ssr can be endure 500v/10A(5).

Thinking of the high temp conditions, I would contact International Rectifier and enquire as to what they might have which might work. I use IR 3510 to switch 50a at 12v, but I don't know about the heat constraints.

It is such a shame that you cannot just go down to the auto parts store and buy a auto starter solenoid... cheap... quick... and easy.

Bill

I need Single pole dual throw SPDT...a common point and one normally open and normally closed, so when not putting out current they connect the battery to the charger.