HT Relay
Ian Bell
discharge the HT when off). Most relays I can find have contacts rated
at 250VAC which translates into a peak of about 350V. However, data is
scarce on what dc voltage these relays can switch. So far I have found
only one that gives a dc current versus voltage curve and that stops at
210V dc (and 200mA) and I really want to be able to switch up to 350V at
up to 200mA. The rest just give a dc voltage at max current value.
So, I am guessing that this problem has been faced before and there are
relays that are known to work fine in this application. Any recommendations?
By the way I prefer a 5V coil.
Cheers
Ian
Jan Panteltje
<ruffr...@yahoo.com> wrote in <hgvunj$ovn$3...@localhost.localdomain>:
You canot use an AC relay rated at 250V for DC at 350V (the sqrt(2) value).
This because, as recently discussed here, in a DC circuit you get arc forming,
and the arc will not extinguish.
Most of those relays have a much lower DC rating.
A simple HV MOSFET perhaps? or transistor?
Else a tube...
Or a real HV relay.
John Fields
wrote:
---
The problem with using relays on DC is that when the contacts open an
arc is established which is hard to put out.
With AC contacts the problem is minimized because as the AC waveform
goes through zero volts the arc is automatically extinguished.
A trick I've seen before, but never used, is to wire two sets of
contacts in series, which will give you twice the effective gap, helping
to quench the arc.
Another trick is to use magnets to "blow out" the arc when the contacts
open, and some larger relays/contactors are designed that way.
Can you use high voltage transistors or solid-state relays instead of
mechanical relays?
---
>By the way I prefer a 5V coil.
---
OK
JF
Ian Bell
> On Thu, 24 Dec 2009 14:44:00 +0000, Ian Bell <ruffr...@yahoo.com>
> wrote:
>
>> I am trying to select a relay for a delayed HT switch (which will also
>> discharge the HT when off). Most relays I can find have contacts rated
>> at 250VAC which translates into a peak of about 350V. However, data is
>> scarce on what dc voltage these relays can switch. So far I have found
>> only one that gives a dc current versus voltage curve and that stops at
>> 210V dc (and 200mA) and I really want to be able to switch up to 350V at
>> up to 200mA. The rest just give a dc voltage at max current value.
>>
>> So, I am guessing that this problem has been faced before and there are
>> relays that are known to work fine in this application. Any recommendations?
>
> ---
> The problem with using relays on DC is that when the contacts open an
> arc is established which is hard to put out.
>
I can understand that with high currents which is why many of the 250VAC
10 or 20 amp relays I have seen are only rated at about 30Vdc for the
same amps but here I am only switching a small fraction of an amp.
> With AC contacts the problem is minimized because as the AC waveform
> goes through zero volts the arc is automatically extinguished.
>
Understood.
> A trick I've seen before, but never used, is to wire two sets of
> contacts in series, which will give you twice the effective gap, helping
> to quench the arc.
>
> Another trick is to use magnets to "blow out" the arc when the contacts
> open, and some larger relays/contactors are designed that way.
>
> Can you use high voltage transistors or solid-state relays instead of
> mechanical relays?
I would rather not.
Cheers
ian
John Fields
wrote:
---
12V coil, and a little pricey, but perhaps something like this, then:
http://www.jenningstech.com/pdf/rel/RF_1D_1E_1G.pdf
JF
Ian Bell
LOL
Cheers
Ian
John Fields
Mark
wrote:
> On Thu, 24 Dec 2009 10:34:59 -0600, John Fields
>
> >On Thu, 24 Dec 2009 16:07:58 +0000, Ian Bell <ruffreco...@yahoo.com>
> >wrote:
>
> >>John Fields wrote:
> >>> Can you use high voltage transistors or solid-state relays instead of
> >>> mechanical relays?
>
> >>I would rather not.
>
> >---
> >12V coil, and a little pricey, but perhaps something like this, then:
>
> >http://www.jenningstech.com/pdf/rel/RF_1D_1E_1G.pdf
>
> ---
> And another:
>
> http://relays.tycoelectronics.com/datasheets/k45c.pdf
>
> And yet some more:
>
>
> JF
Also I would think there is benefit to adding an RC snubber network
across the contacts.
You can even get fancy and add diodes to provide independent "attack"
and "deacy" time constants...
Mark
Martin Riddle
"John Fields" <jfi...@austininstruments.com> wrote in message
news:f827j5dotam4ic9jd...@4ax.com...
Kilovac?
<http://relays.tycoelectronics.com/kilovac/>
Cheers
Phil Allison
"Jan Panteltje"
Ian Bell
>> So far I have found
>>only one that gives a dc current versus voltage curve and that stops at
>>210V dc (and 200mA) and I really want to be able to switch up to 350V at
>>up to 200mA.
>
>
> You canot use an AC relay rated at 250V for DC at 350V (the sqrt(2)
> value).
> This because, as recently discussed here, in a DC circuit you get arc
> forming,
> and the arc will not extinguish.
** Course you can, if you de-rate the breaking current figure sufficiently.
The OP has, like YOU, made a blunder in his interpretation of the specs.
.... Phil
Jan Panteltje
<phi...@tpg.com.au> wrote in <7pif8h...@mid.individual.net>:
>
>"Jan Panteltje"
> Ian Bell
>
>>> So far I have found
>>>only one that gives a dc current versus voltage curve and that stops at
>>>210V dc (and 200mA) and I really want to be able to switch up to 350V at
>>>up to 200mA.
>>
>>
>> You canot use an AC relay rated at 250V for DC at 350V (the sqrt(2)
>> value).
>> This because, as recently discussed here, in a DC circuit you get arc
>> forming,
>> and the arc will not extinguish.
>
>
>** Course you can, if you de-rate the breaking current figure sufficiently.
Sigh, hey, zero current may work!
How clever of you:-)
But wanna bet he wants to switch some more current then zero?
> The OP has, like YOU, made a blunder in his interpretation of the specs.
Got nothing for Christmas Phil?
Phil Allison
"Jan Panteltje"
"Phil Allison"
>"Jan Panteltje"
>> Ian Bell
>>
>>>> So far I have found
>>>>only one that gives a dc current versus voltage curve and that stops at
>>>>210V dc (and 200mA) and I really want to be able to switch up to 350V at
>>>>up to 200mA.
>>>
>>>
>>> You canot use an AC relay rated at 250V for DC at 350V (the sqrt(2)
>>> value).
>>> This because, as recently discussed here, in a DC circuit you get arc
>>> forming, and the arc will not extinguish.
>>
>>
>>** Course you can, if you de-rate the breaking current figure
>>sufficiently.
>
> Sigh, hey, zero current may work!
** Only a bullet in the head would work on you
- you fucking illiterate wog idiot.
..... Phil
John Fields
wrote:
---
I just found this, which might help:
http://schrackrelays.com/appnotes/app_pdfs/13c3236.pdf
JF
