Precharge system for relays

[richcj10]

I am working on this system to protect the contacts of the relays by "pre-charging" the other side. This system detects the "start" line go high and it should turn discharge off. It would then turn precharge (AIR BOT - Pre) on for 5  seconds and then turn AIR -TOP while turning off precharge.  this works on the bench with a power supply. I put this in the project and it stops working immediately. There is nothing wrong with the wiring in the project. any ideas?

[aargee]

Not that I've looked at the circuit closely, but a number of my design transition problems from bench to application usually come down to the power supply and assumptions there of.

Weaker, different, wrong voltage...

[richcj10]

I will take a look at the voltages....maybe a grounding issues?

[David_AVD]

From the MIC5014 data sheet:

V+ Supply. Must be decoupled to isolate from large transients caused by the power MOSFET drain. 10?F is recommended close to pins 1 and 4.

Can't see those caps on your schematic.   

[richcj10]

I noticed that. It is added on the board dead bug style across 1 and 4.

[David_AVD]

What are the differences between the bench and and "real" setup ?  Power, loads ??

[David_AVD]

I noticed that. It is added on the board dead bug style across 1 and 4.

I don't know about anyone else, but it annoys me when people ask for help and the posted schematic is not the same as the actual one.   

[richcj10]

Sorry about it. I thought of it earlier and tried it. forgot to mention it. I found adding more capacitance to the 5v rail helped.
This is wired because there is already a 10uF cap on there after a 7805. Adding another 10uF fixed it. the 10uF cap (and 7805)  is really close to this part of the circuit. Well, it works...