Re: Relays - plea for help!

[Nigel Orr <nigel.orr@xxxxxxx>]

At 10:16 12/10/99 +0100, you wrote:
>'Min current', which presumably means minimum sink from the mains side
>for it to switch on properly, is 100mA. Max off state leakage is 15mA.

Could that be the problem?  Assuming you are driving a relay, when you try
to switch it off, there could still be 15mA flowing, which might be enough
to keep the coil almost energised, just not enough to switch it on in the
first place?  That would explain the 60V reading, if there was, say, 10mA
of leakage, and a 6k ohm coil.

If you have a look at the MK relays on pg 947 of the catalogue, the 240V
coil ones only draw 9mA, so could easily be held on with the leakage
current, even if it is only 5mA or so.  One of the other mains ones has a
7.3k ohm coil, which would suggest about 32mA steady state.  Check how much
current it actually draws when the relay is activated.  You might only need
something like RA56L, on pg 779, which will drive up to 100mA, with a fast
blow fuse in series to avoid damage if you subsequently replace the boiler
with a different type... again, SSRs aren't my field of expertise... but as
RA56L is only about a quid, it might be worth a shot (it's the
zero-crossing version, but you will need a series resistor for the LED (680
ohms or thereabouts)).

If the current is higher, you will need to pick a driver triac which will
suit- if you measure the current, let us know!

>Just to clarify, the SSR can switch the boiler on fine, but it can't
>switch it off properly.

Oops, yes, I did misread that in your initial posting...

Nigel
--
Nigel Orr                  Research Associate   O   ______
Underwater Acoustics Group,              o / o    \_/(
Dept of Electrical and Electronic Engineering     (_   <   _ (
University of Newcastle Upon Tyne             \______/ \(

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