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<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Mick – </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>I would advise using a mechanical relay –
probably a MDR (Mercury Displacement Relay) as they are very quiet, no arcing
and very reliable. </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>There still will be some noise made when
the inverter’s internal relay switches over – so not sure if using
a SSR or MDR will really make that much difference. SSRs can be hard to
troubleshoot when they do have problems… and they are expensive. </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>One extremely good relay I have had very
good luck with over the years is the old Potter & Brumfield PBR type of
relays – big open frame type clunkers. Grainger stocks them and
also offers a nice NEMA 1 “dust cover” metal enclosure to house
them which has nice knockouts but is very compact. Only downside is a
fairly good clunk when it switches. This is a DPDT type 30 amp relay –
and would be the cheapest reliable option. </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Here is a link: <a
href="http://www.grainger.com/Grainger/items/5X848"><font color=black><span
style='color:black'>http://www.grainger.com/Grainger/items/5X848</span></font></a>
available also with 120VAC or 12 & 24 VDC coils. </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Relay: $ 34.50</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Dust Cover: $ 16.00</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Christopher</span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Christopher Freitas</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Director of Research and Development
</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>OutBack Power Systems, Inc.</span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'><a href="mailto:cfreitas@outbackpower.com"><font
size=3 color=black><span style='font-size:12.0pt;color:black'>cfreitas@outbackpower.com</span></font></a></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Tel 360 435 6030</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Cell 360 202 4239</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><font color=black><span style='color:black'>19009 62<sup>nd</sup>
Ave NE</span></font><font color=black><span style='color:black'> </span></font></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><font color=black><span style='color:black'>Arlington</span></font><font
color=black><span style='color:black'> </span></font><font color=black><span
style='color:black'>WA</span></font><font color=black><span style='color:black'>
</span></font><font color=black><span style='color:black'>98223</span></font><font
color=black><span style='color:black'> </span></font><font color=black><span
style='color:black'>USA</span></font></span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'><a href="http://www.outbackpower.com/"><font
size=3 color=black><span style='font-size:12.0pt;color:black'>www.outbackpower.com</span></font></a></span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'> </span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'> </span></font></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:black;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:black'> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Mick Abraham<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, April 29, 2009
10:21 AM<br>
<b><span style='font-weight:bold'>To:</span></b>
re-wrenches@lists.re-wrenches.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [RE-wrenches] Solid state
relay (SSR) questions</span></font></p>
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style='font-size:12.0pt;color:black'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt;color:black'>Hello, Wrenchers and special greetings to
the silicon gurus to whom I address these questions about solid state relays.<br>
<br>
A client wants a gizmo to connect grid "AC In" to their
inverter/charger when the battery voltage is low...resembling the LBX function
on the good ol' Trace SW inverter. The grid power would feed into a 120/240
Magnum inverter/charger which is rated for 30 amps pass through on each hot
leg.<br>
<br>
I may use a solid state relay for the heavy lifting: double-pole, single-throw,
normally open...with DC for the control voltage. Using a voltage controlled
switch, I'll send battery DC to the SSR when the battery voltage goes too low
for too long; then I'll remove that DC trigger when the battery voltage
recovers.<br>
<br>
Question 1: Are SSR's suitable for the variety of loads (including motors) that
this circuit might carry?<br>
<br>
Question 2: Should the SSR be massively over-rated relative to the expected
load (as with typical electronic design practice)? <br>
<br>
McMaster-Carr stocks solid state relays with built in heat sinks; model 7456K43
is published for 30 amps @ 230 volts AC. If protected with a 30 amp double-pole
breaker, would this relay suffice long term or would it instead produce
expensive smoke? (Let's assume free air conditions around the heat sink and a
90 degree F ambient temperature.)<br>
<br>
Question 3: Should I instead bump up to model 7456K44 with a 50 amp rating for
this 30 amp pass through situation?<br>
<br>
I like the idea of no moving parts/no arcs/no clunks compared to a mechanical
power relay, but I also want no customer callbacks. High speed switching (pulse
width modulation) is not one of our requirements, so... <br>
<br>
Question 4: ...is it bad strategy to even consider using an SSR for this
application?<br>
<br>
Thanks in advance,<br>
<br clear=all>
Mick Abraham, Proprietor<br>
<a href="http://www.abrahamsolar.com"><font color=black><span style='color:
black'>www.abrahamsolar.com</span></font></a><br>
<br>
Voice: 970-731-4675</span></font></p>
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