windinmysails
- Mar 12, 2012
- 26
- Joined
- Mar 12, 2012
- Messages
- 26
Hi everyone,
I'm new here, so please forgive me if I'm posting in the wrong place or I'm missing that someone's already asked this question, but I'm having a problem with a project I'm trying to do and I can't see why!
I'm using a Velleman P8055-1 (sometimes called K8055) to drive a couple of relays to make a motor drive in two directions. Basically I'm using 2 channels, each one driving one relay independently and the relays are double pole with one pole connected to ground and the other to 24V. The motor sits across the common pins of the relays so that if I have neither channel on there both relays are off and both inputs to the motor are ground. If I have relay 1 on and relay 2 off, left side of motor receives +24V, right side gets grnd therefore motor goes clockwise. Relay 1 off, Relay 2 on, motor goes counter –clockwise. Both on and motor receives 24V both sides and doesn’t move.
So that’s my theory… I’m using 24V relays (RS: 699-5954) – they come with a built in diode so no need for me to add one. I measured and they draw about 70ma each so this was inside the output of what the ULN2803APG should have been able to do on a single channel, but I wasn’t sure about what happens if both fired at once (although this wasn’t something I was planning as it had no effect on the output side). Anyway, I tried and it worked, but then the ULN chip blew up – so I replaced it with a ULN2803AN which should sink 500ma (if I’ve understood correctly). But the same thing happened…
Can anyone tell me what I’m doing wrong here? I’ve driven lots of smaller things before and they’ve always worked fine. Is it because this is 24V (I can’t see how, but I don’t know). Is it something to do with the surge of the motors starting up? Help!
Many thanks in advance for any assistance!
Neil
I'm new here, so please forgive me if I'm posting in the wrong place or I'm missing that someone's already asked this question, but I'm having a problem with a project I'm trying to do and I can't see why!
I'm using a Velleman P8055-1 (sometimes called K8055) to drive a couple of relays to make a motor drive in two directions. Basically I'm using 2 channels, each one driving one relay independently and the relays are double pole with one pole connected to ground and the other to 24V. The motor sits across the common pins of the relays so that if I have neither channel on there both relays are off and both inputs to the motor are ground. If I have relay 1 on and relay 2 off, left side of motor receives +24V, right side gets grnd therefore motor goes clockwise. Relay 1 off, Relay 2 on, motor goes counter –clockwise. Both on and motor receives 24V both sides and doesn’t move.
So that’s my theory… I’m using 24V relays (RS: 699-5954) – they come with a built in diode so no need for me to add one. I measured and they draw about 70ma each so this was inside the output of what the ULN2803APG should have been able to do on a single channel, but I wasn’t sure about what happens if both fired at once (although this wasn’t something I was planning as it had no effect on the output side). Anyway, I tried and it worked, but then the ULN chip blew up – so I replaced it with a ULN2803AN which should sink 500ma (if I’ve understood correctly). But the same thing happened…
Can anyone tell me what I’m doing wrong here? I’ve driven lots of smaller things before and they’ve always worked fine. Is it because this is 24V (I can’t see how, but I don’t know). Is it something to do with the surge of the motors starting up? Help!
Many thanks in advance for any assistance!
Neil