DC relays capable of 150Vdc & 3Amps? 1

[drjorde]

I am searching for an ATEX and CSA/UL approved thermostat or relay capable of switching 150Vdc at 3Amps. We have an application that can only use DC and needs to comply with these certifying bodies. The relay must either be hermetically sealed or solid state.


DrJorde

http://plansbyjorde.tripod.com

 

[itsmoked]

I think you are going to have a real problem with that...ATEX

What about a regular relay in an EXP enclosure?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

This one (

http://my.eurotherm.co.uk/WebStore/tabid/36/List/0/ProductID/1/Default.aspx

) is probably overkill. But it shows that such animals exist. CE, but no ATEX marking. Is it the marking or the function you need?

Gunnar Englund

http://www.gke.org

 

[itsmoked]

Skoggs I thought ATEX was "explosion proof". Did I get that wrong?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Yes Keith,

You are right. ATEX is a new European thing. Or, should we say old thing with a new name. There is a guide 94/9/EG describing it. Used for equipment operating close to or in environments that contain fumes and dust.

I guess that I just answered the headline's question about a DC relay. Didn't realise that ATEX marking was a requirement.

Gunnar Englund

http://www.gke.org

 

[drjorde]

I won't go into all the details, but in short EP boxes are not possible.
Being a World class supplier of Turbines with on-skid controls means we have to have all the certifications. On-skid controls don't work in -40 deg F weather. I need to be able to heat these boxes to at least 0 deg F in order to get touch screens and IO modules, PLC's into a safe temperature range. AC is not permitted, and many cases not available. All the thermostats I can find either don't have the certs or won't handle the DC and current. I thought of using a relay if I can find one that has the rating and can be used in hazardous locations.
This is not a one time deal, I'm working towards having a standard that will be able to be sold in any country worldwide.

DrJorde

http://plansbyjorde.tripod.com

 

[Skogsgurra]

An alternative would be to use a thermistor to control one or several power transistor(s). The power dissipated in the transistor(s) will also be the power needed to heat the housing. It can all be potted in epoxy, leaving the mounting surface of the cooling element exposed.

Gunnar Englund

http://www.gke.org

 

[drjorde]

Skoggs
I need 420 watts in extreme cases. We are looking at using 3ea 140 watt heaters in parallel with a single TC and Relay or thermostat. The heaters are running on 120 Vdc, but the Charger when it kicks in goes up to 150Vdc, hence the high limit. This equates to almost 3Amps at that voltage. We found a thermostat that meets everything but the current. It will only handle 200Ma.

DrJorde

http://plansbyjorde.tripod.com

 

[jraef]

ATEX approval is going to be the bigger problem here, there are plenty of DC SSRs out there.

I know this may be problematic with RoHC now, but Mercury Displacement Relays might work. They can be ordered as UL Class 1 Div. 2 Exp. Proof but I don't know how that relates to ATEX. Look at the 35/60A version, that's the ones that mention ExP as an option. A little overkill, but at least it might work.

MD relay link

Another alternative would be Allen Bradley's hermetically sealed control relays, Bulletin 700R. They use reed switches rated for up to 5A DC and have approval for Cl 1 Div 2 as well. I don't see ATEX approval on them however, but you could always ask.

AB 700R relay link

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[ourious78]

You definately want to stay with Solid State for the intrinsicaly safe route, if that is a concern. The idea that skogsgurra suggested is the right way, just add a capacitor in the incomming line to the charger to absorb the shock from the draw. You could use an opamp and some resistors to turn on the transistors when power is needed but a thermistor will work as well.

 

[drjorde]

RoHS and WEEE which are being adopted by California as SB20 Jan 1, 2007 will pohibit the use of mercury.

AB has an office in my department and we are, I think, their biggest account worldwide. Anyway, they have not been able to step up to the plate on this either.

I need a SSR manufacturer that will apply for the certs required and we will even help pay for it. A certified assembly would even be better.

DrJorde

http://plansbyjorde.tripod.com

 

[danw2]

Here's a lead for you. I've used these United Electric switches before and one model has ATEX rating, and it isn't clear to me whether it is EXP rated or IS rated. But it's a commercially available temperature switch that will handle 5A.

http://www.ueonline.com/bulletins/12-b.pdf

See page 8 of the 16 page pdf for the 12 temperature switch
See page 11 for the M405 ATEX rating option, & the M423 ATEX junction box,
Maybe you'd need that M460 external grounding screw

If I understand your app, you need the internal panel temperature to be monitored.

It looks like this switch (like their others) can have an integral bulb sensor, for local monitoring, or a bulb on a capillary tube for remote temp monitoring (Mount the switch 6' from the bulb.)

I've worked with these switches for US EXP applications, and I recommend the M201 (factory setting) option for ease of construction - whoever installs it takes it out of the box, wires it up and they're done. It's too easy for contractors/assemblers/installers to overlook the calibration or setting of the switch. (although I've only used the pressure models not the temperature models, presumably temperature can be factory set as well).

They have other models of switches, many of which are FM Class 1 Div 1 for EXP, but I'm not sure whether the others have the ATEX rating. Having spec'd this Spectra model recently, I recalled the ATEX option on the Spectra 12, but I'm sure their distributor can help you out to see if another one might be more suitable.

Dan