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nuckolls.bob(at)cox.net
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 Posted: Sun Oct 21, 2007 2:53 pm Post subject: Solid State Relay Alert |
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Solid state "relays" for AC have been around for decades.
They generally use Triacs as the control device, are designed
for use at 120VAC and above and drop about 1.5 to 2 volts in
the "turned on" mode . . . not a big deal in a 120VAC circuit.
I've been watching a number of new solid state relay products
popping up for the DC world. They have the general appearance
of the photo posted here:
http://www.aeroelectric.com/Pictures/Relays/Solid_State_Relay.jpg
I've purchased a couple of exemplar products and was disappointed
to find that while they were "rated" for service in systems down
to 12VDC, their turned-on voltage drop was about 1.5 volts at
full load. The critter shown above was rated at 40A . . . but
would need a healthy heat-sink to get rid of the wasted energy.
These are not suited for use at 14V and only marginally suited
for 28V. I'll keep watching . . .
Bob . . .
----------------------------------------
( "Problems are the price of progress. )
( Don't bring me anything but trouble. )
( Good news weakens me." )
( -Charles F. Kettering- )
----------------------------------------
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Nuisance
Joined: 10 Jan 2006
Posts: 9
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| Posted: Mon Oct 22, 2007 5:16 am Post subject: Re: Solid State Relay Alert |
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Bob, is this a bi-polar device? !.5 Volts drop is pretty typical for a darlington.
Wouldn't the power FET based SSRs do pretty well at the 5 - 10 Amp load range common for lights, fuel pumps, radios, etc.?
John
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nuckolls.bob(at)cox.net
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| Posted: Mon Oct 22, 2007 3:43 pm Post subject: Solid State Relay Alert |
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At 06:16 AM 10/22/2007 -0700, you wrote:
| Quote: |
Bob, is this a bi-polar device? !.5 Volts drop is pretty typical for a
darlington.
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Don't know what the internal technology is . . . only
that 1.5V is 10% of system voltage in the switching device
alone!
| Quote: | Wouldn't the power FET based SSRs do pretty well at the 5 - 10 Amp load
range common for lights, fuel pumps, radios, etc.?
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FETs or arrays of FETS can be used to
produce exceedingly low on-resistances.
Under 1 milliohm is now quite practical.
This would toss off 20 mv at 20A for a
grand heat load of 400 milliwatts. That's
MY kind of heat sink problem.
Point is that this particular product,
no matter how attractively priced, is
not ready for top billing in our airplanes.
I think I gave under $10 for the one in
the picture. I had hopes. We're getting
close but not quite there yet.
Bob . . .
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hdwysong(at)GMAIL.COM
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| Posted: Tue Oct 23, 2007 12:52 am Post subject: Solid State Relay Alert |
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> Point is that this particular product,
> no matter how attractively priced, is
> not ready for top billing in our airplanes.
> I think I gave under $10 for the one in
> the picture. I had hopes. We're getting
> close but not quite there yet.
>
> Bob . . .
The DC SSRs from Crydom (e.g. - D06D series) are the same
"brick" form-factor as the Chinese knock off you picked up
(and admittedly more expensive), but the spec voltage drop
on a D06D60 (60 ADC model) at rated load is 0.6 V vs 1.5 V.
Still 5% on a 12V system, but are we throwing the SSR baby
out with the Chinese bath water here?
Any idea how the heat dissipation requirements for these
critters compare with the tried/true S701-1 contactors
operating at the same load? I know the "can" contactors get
"warm", too, but I'm wondering if we can quantify "warm" in
order to to make an apples-to-apples comparison?
I'm also wondering how we would factor in the "wasted" power
on the S701-1 coil, additional durability of the SSR device,
etc., into our trade study.
Thanks as always for the insight and education, Bob.
D
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Tue Oct 23, 2007 6:10 am Post subject: Re: Solid State Relay Alert |
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Bob, et al,
For a couple years I have been selling the 35A "Powerlink Jr." Solid State Relay on my website.
The device is based on an International Rectifier IRF2804 which has a maximum 10V Rds(on) of 0.0023 Ohms.
The device has a hold-on current of 200 microamps, weighs 3.1 ounces, and has it's own heat sink.
http://www.periheliondesign.com/powerlinkjr.htm
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Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net |
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nuckolls.bob(at)cox.net
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| Posted: Tue Oct 23, 2007 7:26 am Post subject: Solid State Relay Alert |
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At 03:55 AM 10/23/2007 -0500, you wrote:
| Quote: |
> Point is that this particular product,
> no matter how attractively priced, is
> not ready for top billing in our airplanes.
> I think I gave under $10 for the one in
> the picture. I had hopes. We're getting
> close but not quite there yet.
>
> Bob . . .
The DC SSRs from Crydom (e.g. - D06D series) are the same "brick"
form-factor as the Chinese knock off you picked up (and admittedly more
expensive), but the spec voltage drop on a D06D60 (60 ADC model) at rated
load is 0.6 V vs 1.5 V. Still 5% on a 12V system, but are we throwing the
SSR baby out with the Chinese bath water here?
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Don't see how . . .
| Quote: | Any idea how the heat dissipation requirements for these critters compare
with the tried/true S701-1 contactors operating at the same load? I know
the "can" contactors get "warm", too, but I'm wondering if we can quantify
"warm" in order to to make an apples-to-apples comparison?
|
The S701 is suited for carrying 200+ amps for cracking . . . it's
also a bi-directional switch. You can both charge and discharge the
battery through its metallic contacts.
Coil power dissipated is on the order of 10W . . . but VOLTAGE
DROP across closed contacts is on the order of 100 mV.
| Quote: | I'm also wondering how we would factor in the "wasted" power on the S701-1
coil, additional durability of the SSR device, etc., into our trade study.
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It isn't just a "wasted power" consideration; we also
have voltage drop across closed contacts. After sizing system
components in a pitot heater circuit to keep wiring and
control losses below 5%, the simple act of replacing
a pitot heat SWITCH with a SS relay suddenly boosts
voltage drops to over 10%.
In the case of the S701, there are no components internal
to the product that become at-risk due to temperature
rise. In a SS relay, you have a semiconductor device that
must be held below certain temperature levels (generally
150C) to avoid killing the device. This is where we become
concerned for efficient conduction of heat into surrounding
environs.
Not necessarily a terrible thing if that meets your
personal design goals . . . but it's not something
I would recommend. I've had a number of inquiries
from readers about the various new kids on the block
and the devices I evaluated were certainly priced right
but short of my design goals.
| Quote: | Thanks as always for the insight and education, Bob.
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My pleasure sir.
Bob . . .
----------------------------------------
( "Problems are the price of progress. )
( Don't bring me anything but trouble. )
( Good news weakens me." )
( -Charles F. Kettering- )
----------------------------------------
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marcausman
Joined: 08 Feb 2007
Posts: 70
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| Posted: Tue Oct 23, 2007 7:29 am Post subject: Re: Solid State Relay Alert |
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Or if you want to take a look at a whole SYSTEM that uses solid-state switching technology, look here: www.verticalpower.com
We do work with conventional contactors for the high current loads, though. When very high-current solid-state relays become practical, I'm sure they will be controllable in the same manner as the current contactors.
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Marc Ausman
http://www.verticalpower.com "Move up to a modern electrical system"
RV-7 IO-390 Flying |
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nuckolls.bob(at)cox.net
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| Posted: Tue Oct 23, 2007 7:29 am Post subject: Solid State Relay Alert |
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At 07:10 AM 10/23/2007 -0700, you wrote:
| Quote: |
Bob, et al,
For a couple years I have been selling the 35A "Powerlink Jr." Solid State
Relay on my website.
The device is based on an International Rectifier IRF2804 which has a
maximum 10V Rds(on) of 0.0023 Ohms.
The device has a hold-on current of 200 microamps, weighs 3.1 ounces, and
has it's own heat sink.
|
Understand . . . and at the present time, you're
the only kid on the block who has addressed the
voltage drop design goals. But there's a dust
cloud rising over the hill and one or more of
those riders is carrying the next great thing
in solid state relays.
Bob . . .
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