DHB question

[jt2ma71]

DHB is wired per 2nd diag. found in the product datasheet, driving two grounded motors in the same direction.

If I just connect the power wires of the DHB to the battery. No wires connected to the inputs, should I get voltage from the DHB output wires?
I am getting 6.5 volts, and when I connect the output to the pumps, obviously they come on right away (ECU/IGN PWR OFF)
As soon as I disconnect the output connector and measure the voltage from the pins again, I get 12volts. Does not matter whether I have the input connector hooked up or not. Does not matter what Output I'm using from the M800 ECU either. If I disconnect it from battery and then reconnect, the voltage drops to 6.5 volts again. So as soon as I reconnect the connectors, the pumps just instantly turn on. Is there something wrong with my DHB? Thanks

[figgie]

Hey Ron!

The DHB acts as a giant FET/MOSFET...

sounds like something is holding the DHB in a partially open position. 6.5V is large amount of Voltage leakage. Could have been caused by over current.

The question is the two motors, what are they and how much amperage do they use? Are they cooling fans?

[jt2ma71]

Well, they are pumps. One is the weldon pump and the new one is a methanol injection pump. I had this hooked up with the DHB controlling the ground feed to the pumps and the POS wires of pumps are connected to the battery. No problems there as long as I use the injector 8 (my last remaining inj. output) to control the second pump. There are no issues with the fuel pump using aux out 3 to control it. Now, I want to use AUX 6 to control the second pump but everytime I turn ign OFF the second pump comes ON.
So, I was told that the preferred way was to have DHB control the hot side of the pumps. I then rewired them as such. Also thinking this might make AUX 6 work. I changed all parameters accordingly. Now, both pumps come on with ign OFF. I've tried different settings and was able to make one pump work as it should but one will still come ON with ignition OFF.
I just went ahead and rewired them back to DHB controlling the ground pump wires and used inj 8 to control second pump. They are now working again as they should and stay OFF with ign off. I'm still curious why all the issues and can't use AUX output 6. I was also told to put a relay on the POWER wire to the DHB to make sure it's OFF when IGN is OFF. I'll probably add that later, I dunno..thanks..

[figgie]

Ron

So if we look at the truth table and also at diagram 3 (motors to + and the other side to Out1 & Out2 on the DHB). Low = Motor On, High = Motor Off.

When the Aux output is low (0v), the Motor is turned on. This is consistant with what you are seeing in Aux 6 when the values are left at default.


If you wired it like diagram 2, when off, the motor will be off when the outputs are left as default.

I attached the images below...(just so we are on the same page )

[SprinterTRD]

The problem you have with both drawings is the DHB is always powered keeping the internal circuits on. The fuse must be connected to the batery through a relay or switch which also powers the ECU.

You have a situation where the ECU is powered off but the DHB is on. Power may be feeding from the input of the DHB into the ECU via the aux PINS creating a voltage drop that is enough to fool the DHB to turn its output on.