MK138 blown diode problem

Kits Mini Kits Range
1

Hi ive got a problem that baffles me.

I create incubators using the same proccess. using a modified mk138 to get the temps to 38 deg C.

some times after a period of successfull operation, the circuit dies.

ive recently discovered from another post that this is a problem, becouse d2 blows.

i would like sort this problem out once and for all.

Could you please tell me IF i am doing something wrong, and do i need another diode to protect the circuit from motor feedback.

I am simply putting a halogen light and 12v dc motor in parallel, these draw no more than 2A total (at 12v)

Also could you tell me what is the maximum current that can be used in these relays SRU 12v-SD-C (since i think the kit contains a different one that it did years ago)

Please can you help me.

many thanks

Regards Pete

2

The blowing of the diode has nothing to do with the load or the relay.
Replace the diode with a 1N400x type and it will never blow again.

3

Make it minimal a 1N4004 … :wink:
Most available is however the 1N4007: more than ok!

4

ok, thanks for lettting me know its nothing to do with the load, but can someone answer me why are they blowing, and why are velleman giving a diode in their kits that they know will blow (for whatever reason its blowing).

many thanks for your support.

regards Pete

5

Please note that of the thousands of units sold, only a few have a problem. The thousands that work are not mentioned on this forum, only people who experience problems come here, so that could give the impression that there is something wrong with the kit.
Most likely, it is a combination of factors that causes this behaviour: rather high input voltage, diode spec at a low limit and electrolytic cap with large tolerance.
In the future, we will consider putting a 1N4007, just in case…