5V Latching Relays

G

Grant Fleming

Senior Member
I am looking to obtain a few relays. I have searched the forums and found the '40c latching relays' that were offered on Ebay previously.
Has anyone been using a latching relay for their PICAXE projects that is readily available & can be driven directly off the pin? A coil using less than 20mA, contacts to switch up to 250Vac with 250mA.
Having searched on-line catalogues of many of the larger suppliers I find many, but the ones with the least coil current are still 30mA.

Cheers

Grant
 
L

leftyretro

New Member
Grant Fleming said:
I am looking to obtain a few relays. I have searched the forums and found the '40c latching relays' that were offered on Ebay previously.
Has anyone been using a latching relay for their PICAXE projects that is readily available & can be driven directly off the pin? A coil using less than 20mA, contacts to switch up to 250Vac with 250mA.
Having searched on-line catalogues of many of the larger suppliers I find many, but the ones with the least coil current are still 30mA.

Cheers

Grant
Click to expand...
I think I was the one that started that thread. The relays are still avalible from that same supplier on E- Bay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=170203912207&ssPageName=STRK:MEWA:IT&ih=007

I measured the actual coil current being drawn as around 13ma I belive. Also keep in mind with a latching relay you don't always have to leave the coil energized continously, just pulsed for say 50-100 ms will do it. Anyway I did experimate with these relays with a Picaxe and was able to reliably operate the relays just fine without protection diodes. It's an easy way to have a picaxe application automatically turn off it's power source. Attached is a drawing on a manual turn on / auto power off circuit.

Lefty
 

Attachments

Last edited:
W

westaust55

Moderator
If I read the data correctly,

1. it requires +3.75 Volts to latch the relay and close the contacts

2. it requires -3.5 Volts to release the relay and open the contacts.

So while the PICAXE signals need only be a pulse, the polarity must be reversed to release the coil.

Would have to consider using two IO so the reverse polarity can be achieve - but on an 08 that uses up 40% of the total IO.
 
L

leftyretro

New Member
westaust55 said:
If I read the data correctly,

1. it requires +3.75 Volts to latch the relay and close the contacts

2. it requires -3.5 Volts to release the relay and open the contacts.

So while the PICAXE signals need only be a pulse, the polarity must be reversed to release the coil.

Would have to consider using two IO so the reverse polarity can be achieve - but on an 08 that uses up 40% of the total IO.
Click to expand...
Yes, two digital outputs would give you full control for both continous or pulsed operation. However If you look at the attachment drawing I showed, you can operate a single coil latching relay with a single digital output. A continous high output will "set" the relay and charge the cap so that later a low output (under your software control) can reset it. The trick is the capacitor charges and stores a charge voltage for resetting the relay. There is probably a maximum speed limit for setting and resetting reliably as the capacitor must reach full charge for resetting, but I'm sure it's less then say 100-200 millisec. Also even though there is a continous high output, the DC current drawn will drop off once the cap charges, and then only the current used by the resistor will be drawn, less then a milliamp. I did breadboard and test this circuit and it worked very well.

Lefty
 
Last edited:
G

Grant Fleming

Senior Member
Thanks anyway for the links guys.
Now I have been able to see the datasheet for the first time.
Max contact voltage: 125Vac. As per my original post, I will be switching 250Vac.
I'll keep looking!

Cheers,
Grant
 
G

Grant Fleming

Senior Member
eclectic said:
Andrew.

I think that's a typo.

The datasheet accessed from this link:

shows 125v

e
Click to expand...
eclectic,

I like that, you give the seller the benefit of the doubt!
In the majority of cases where superior specifications are advertised it is no accident/typo!

Cheers,

Grant
 
Last edited:
G

Grant Fleming

Senior Member
eclectic,

Quite expensive that relay in the link!
The idea from Flooby is clever, I may keep it in mind to experiment with sometime - but I would like to latch a relay so that it stays in that state even with my project powered down. I might just use a transistor to switch to the relay coil of a 5V minature relay that has switching contacts suitable for 240Vac.

Cheers,

Grant
 
Last edited:
You must log in or register to reply here.
Top