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Forum Index : Windmills : Solid state relay suitable for brake
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| carl1 Regular Member  Joined: 16/04/2007 Location: AustraliaPosts: 79 |
Hello to all Can anybody tell me if solid state relay is suitable to use as brake relay: I would like to use a 3phase SSR to connect the 3 phases of my wind generator to 3 Thermistors. ( soft brake ) SSR data: input DC 3-32V, output 520vac 25a Is the ac output side only conductive at a certain min. voltage or frequency? SSR like this: http://cgi.ebay.com.au/ws/eBayISAPI.dll?VISuperSize&item=140 429818845 cheers Harald |
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| davef Guru  Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Link doesn't work for me. Try dropping a copy of it into the message using 4th button along just above the message window. 520V at 25A = 13Kw (each phase) How much power do you hope to generate? No minimum frequency, but maybe a maximum frequency. The voltage drop across a MOSFET output is fractions of a Volt. I am assuming they are MOSFETs. If you are turning a MOSFET switch on using a rectified voltage derived from the 3 phase there will be some minimum, like 5-10Volts. But, you aren't worried about having to turn them on at low voltage. How much power can these thermistors dissipated? Can you provide a link to these beasts? |
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| carl1 Regular Member Joined: 16/04/2007 Location: AustraliaPosts: 79 |
Hi Dave first :Forget the link I put in. I will put new one in. Here are more details: The thermistors get connected between the phases before the rectifier, more or less in parallel with it when the relay is on. So Ac is going across the NTC and only part of the load/ amps per phase.So the moment the Voltage drops below battery voltage the thermistors take all of the load and slows the generator down. Thermistors: Typ Ametherm SL32 2R025 Resistance @ 25°C 2.0 Ω ± 15% Max Steady State Current Up to 65°C 25.0 A Max Recommended Energy Rating 300.0 J Actual Failure Point of Instantaneous Energy 548.0 J Resistance @ 100 % of Maximum Current 0.024 Ω Resistance @ 50% of Maximum Current 0.055 Ω Body Temperature at Maximum Current 236 °C Dissipation Constant 45.4 mW/°C They might be a bid to big for my wind generator: output max 500 Watt, 12v,@ 960rpm, 80hz, 10- pole motor. Relay 3-phase or 3 in series SSR relay, 15amp would be enough. like SSR relay or SSR 3-phase On the data for output voltage on SSR there is always a voltage range nominated. So the question is when the generator is slowed down, voltage close to 0, frequency as well close to 0, does a SSR stays conductive on the output side? thanks Harald |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
//www.crydom.com/en/Products/Catalog/AdvancedWebPage.aspx]da tasheet on this page[/URL] They only appear to give ratings from 43-67Hz or 50-60Hz, so you are trying to navigate uncharted waters. Minimum turn-on voltage 4.0 Volts. You would be deriving your control voltage from the battery bank so no problem here. They have low capacitance, so would have expected a fairly max operating frequency. Maybe an email to the manufacture would get you some real test data. Just curious about the reason for doing this. Is this so you don't need to build a diversion load? Save wear and tear on the gennie when the batteries are fully charged? Will these thermistors provide enough braking at high wind speeds or do you have another way of handling that? |
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| Chipboy Newbie  Joined: 13/12/2006 Location: AustraliaPosts: 16 |
Be cautious with SSR they are designed for the 50/60 Hz power we normally use, the high frequency AC from a mill will give issues with the zero crossing detecton, I daresay it will not be fast enough to work reliably. Matt VK4KLM Wind wannabe |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Carl If you want to go this way why not use a conventional 3 phase relay, I have seen them for sale 80 amp on ebay for $30/40 240 volt coil could run off the inverter and wouldn't run long enough to be a problem. No frequency problems to worry about, once the mill is stopped no current, you could use a three pole switch for holding. All the best Bob Foolin Around |
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