# microcontroller crash problem

#### jpanhalt

Joined Jan 18, 2008
10,515
the problem occurs when I use a load behind for the relays to switch between 0v and 230v
Stepping back a little, does that comment mean that when no load is switched by the relay there is no problem, but when the relay contacts switch a load, the problem occurs?

If so, maybe the problem is related to arcing at the contacts.

#### ouafae

Joined Jun 11, 2019
52
Yes, there is an arc at the relay contact levels, that's why I inserted the diode but maybe it's necessary to add an RL circuit to slow down the priming

#### ouafae

Joined Jun 11, 2019
52
Sorry i mean RC circuit

#### ericgibbs

Joined Jan 29, 2010
11,122
Hi,
If your circuit diagram is correct and you have a 40R inductor in series with the 5V input and you are switching a 125R relay coil, powered from the output end of the 40R inductor, then the 5V supply to the circuit will drop to 5v* (125/(125+40)) = 3.7V while the relay is energised.

So please check the actual resistive value of that inductor and its location in the 5V line.

E

#### ouafae

Joined Jun 11, 2019
52
I'll start reviewing the inductance. Thank you to all of you. I really like this group even I don't speak much English, it's very interesting and its members are capable.

#### LesJones

Joined Jan 8, 2017
2,726
You have not yet answered the question about the nature of the 230 volt AC load that is being switched by the relay contacts.

Les.

#### ouafae

Joined Jun 11, 2019
52
You have not yet answered the question about the nature of the 230 volt AC load that is being switched by the relay contacts.

Les.
it is Three phase, stationary test system

#### LesJones

Joined Jan 8, 2017
2,726
How can a single contact be switching a three phase load ? You have not said if the load is resistive or inductive what current is being switched and what spark suppress measures have been taken. The more information you supply the more likely someone will come up with the solution.

Les.

#### Sensacell

Joined Jun 19, 2012
2,631
1) Ditch that inductor in the 5V, it's not helping

2) Install snubber networks across the relay contacts.

#### ouafae

Joined Jun 11, 2019
52
How can a single contact be switching a three phase load ? You have not said if the load is resistive or inductive what current is being switched and what spark suppress measures have been taken. The more information you supply the more likely someone will come up with the solution.

Les.
the load is resistive, I use three contacts.
by adding 2 contacts to the schematic I filed, all three seem to be.

#### ouafae

Joined Jun 11, 2019
52
i.e. I completely remove the inductance.
I plan to do a test without inductance. What do you think?

#### LesJones

Joined Jan 8, 2017
2,726
I don't understand your answer. Your relay is a sealed single pole unit so how can yo add extra contacts to that ?

Les.

#### ouafae

Joined Jun 11, 2019
52
[QUOTE = "LesJones, post: 1414426, member: 406475"] Je ne comprends pas votre réponse. Votre relais est une unité unipolaire scellée, alors comment pouvez-vous ajouter des contacts supplémentaires?

Les. [/ QUOTE]

#### Xavier Pacheco Paulino

Joined Oct 21, 2015
728
i.e. I completely remove the inductance.
I plan to do a test without inductance. What do you think?
But didn't you say you have the same issue before the inductor?
no,
Indeed, I inserted this inductance to remove the current peaks due to relay switching.
You mean maybe there's a voltage drop because of the inductance. Right?
But yes, remove the inductor anyways.

#### LesJones

Joined Jan 8, 2017
2,726
So that means that the voltage drop due to the resistance of the inductor will be much worse than our calculation based on a single relay. So with 3 relay coils in parallel the voltage will drop to (125/3) / (40 + (125/3)) x 5 volts = 2.55 volts.
So the three relays are directly switching a 230 volt three phase supply into a purely resistive load (I assume a heater) but you still have not told us what current they are switching. Also is the 230 volts phase to phase or phase to neutral.

Les.

#### ouafae

Joined Jun 11, 2019
52
I measured the voltage across the inductance I didn't have a voltage drop. But I just want to test without inductance if I have the problem or not

#### ouafae

Joined Jun 11, 2019
52
hi,
I changed the inductance value to 10 ohm but I fell on permanent closing and opening. so the pre-problem does not become inductance.

#### bertus

Joined Apr 5, 2008
20,881
Hello,

When you are using three relays in parallel, the transistor has to switch 120 mA.
As said before, R10 (4k7) will have a to high value.
Reduce the value to 470 Ohms.

Are you really using three relays in parallel?
The BC846 can only handle 100 mA.
The three coils in parallel draw 120 mA.

Bertus

#### ouafae

Joined Jun 11, 2019
52
this is my complete schema

#### Attachments

• 59.9 KB Views: 2

#### ouafae

Joined Jun 11, 2019
52
i. e. I leave the inductance value 40 ohm and change the value of R10.