DC relay for 48V Power Vent [RE-wrenches]

Tue Feb 19 14:58:52 PST 2008

John - 

You are right that most of the small relays you will find do not have a
very high DC rating - but I have not seen any problems with using 30VDC
rated relays in applications like vent fans.  They are very low current
and are also operated from a brushless fan drive - so the currents are
well controlled and there is virtually no start up current involved. 

I would not advise using a typical "automotive" relay for this however -
they do not have the contact spacing - these are usually not rated for
120VAC either.  Go with a socketed type relay with a clear housing so
you can see if the arcing is excessive or discoloration of the cover
occurs.   

One trick to also keep in mind is that you can also wire multiple poles
of a relay in series to increase the voltage tolerance - although this
is not shown in the product literature it is pretty common in the
control world and also the electric vehicle conversion marketplace.  So
wire up a 30VDC 4PST relay into a 120VDC SPST relay for example.  I have
seen these work well for years on EV conversions with big loads at high
voltages (120VDC) such as heaters etc. which have high inrush currents. 

Christopher

Christopher Freitas
Director of Research of Development 
OutBack Power Systems, Inc.
cfreitas at outbackpower.com
Tel 360 435 6030
cell 360 202 4239
19009 62nd Ave NE 
Arlington WA 98223 USA
www.outbackpower.com

-----Original Message-----
From: John Raynes [mailto:john at raynes.com] 
Sent: Tuesday, February 19, 2008 1:15 PM
To: RE-wrenches at topica.com
Subject: DC relay for 48V Power Vent [RE-wrenches]

I'm sure this has been covered some time in the past, but with the
Topica 
search function being kaput...

Does anyone have a part number for a relay for switching a 48V Power
Vent 
from an MX60 aux output, one that has worked well for them?  I know I
could 
have ordered the 12V model, and powered it directly, but I didn't.  I 
assume the relay I need is going to have a 100V-125VDC rating, since no
one 
to my knowledge makes a relay with 70-80 volt ratings.  That usually
means 
mercury-wetted or solid state for DC relays.  Without getting too exotic
or 
pricey I thought someone may know of a model that works well and mounts
to 
a relay socket or DIN rail.

Thanks,
John Raynes
RE Solar
Torrey, UT

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