I signed up to ask a question on another part of the forum so I thought I would balance that with a contribution here by sharing this circuit I designed and fitted to my B300 based 1973 motorhome. It's a good fun project for winter evenings (see schematic drawing file attached - I hope).
Avoids having to repeatedly reach over and flick the wiper switch when it's only slightly raining which is a pain (right?).
So the circuit provides a variable wiper delay of 5 - 19 seconds between wipes. I works independently so the wipers don't need to be switched on. If they are switched on they just wipe normally regardless of whether the delay control is on or off.
My basic idea was a bit too simplistic as it turned out - I thought: just send repeated short pulses to the wiper motor as if I was flicking the wiper switch myself, make the pulse short enough to allow the wipers to park themselves in between until the next pulse comes along.
That turned out to be a little naive because, after I got the circuit mocked up and working on the bench, I then found a problem interfacing with the Dodge wiper park wiring, not having looked at the wiper wiring diagram until after I built the circuit! (see below my solution).
As for components - the 555 timer chip and LM7805 5v voltage regulator chip can be bought for peanuts. The 5th pin on the timer chip is not used. The other components are common and dirt cheap and "near enough" alternatives should work fine.
In case anyone is wondering, the lower diode makes the pulse short and the delay long. Without it the pulse and delay would be much closer to the same duration.
For the 80K variable resistor I used the volume control from an old car radio set which usefully doubles up as the on/off switch, it also gives you something you can easily fit to the dash without looking too wrong. I tested a couple of radio volume controls and they were both around 80K ohms but I'm sure the other components could be adjusted to accommodate a different value.
Of course you need to have the "park" function already working OK on your wipers (which mine wasn't - another story). You also need to fit a relay (standard 12v 30A is fine) and use the circuit to ground the -ve side of the relay coil using the signal wire shown on my schematic. The upper diode in the schematic is just for "fly-back" protection to the transistor when the relay coil switches off. I mounted my relay close to the wiper motor and powered the +ve side of the coil from the steady +12v wire that goes to the motor (on mine a pink wire) which means it gets voltage when the ignition is switched on.
Now to the complications regarding the way the factory park circuit wiring is laid out. This applies to 1973 Dodge two speed wipers but I'm sure others may be similar (or different in a similarly tricky way) so definitely necessary to check factory wiring diagrams first or you can short something.
Basically the factory park circuit shorts out the motor tails when the wipers go into "park" position (it is designed this way to make the wipers stop dead rather than carrying on to a more gradual stop and possibly shooting right through park and into the next wipe). It does this using a connection in the wiper switch plus an internal switch inside the motor which goes to ground when the wipers park. The result is you can't just give the motor +ve wire 12v to start the wipers moving because that connection is actually switched to ground internally when they are off and parked !!
The way I got around this was to use a two pole relay which maintains the ground connection through the internal park switch when the relay is off (so the wipers park as Dodge intended), but when the relay is energised it interrupts that conection and switches the motor wire to +12v instead. On my vehicle that involved placing the switching part of the relay between the blue and pink wires as shown in the little box on the schematic.
In summary - it works great but make sure you understand the wiper wiring before you try it. In my 1972 National Service Data book the blue and pink wires on my vehicle are actually shown as green and blue, so obviously Dodge did sometimes use different colours for these.
Re: DIY intermittent wipers for early vans (Dodge in my case)
#731697 January 11th 2018 5:25 pmJanuary 11th 2018 5:25 pm
Yeah I read some of wrcsixeight's stuff about leisure battery charging relays, which is a job I need to get to. I just have a manual switch at the mo.
Anyway thanks for the feedback, but I just realised ON MY SCHEMATIC I'VE DRAWN THE PROTECTION DIODE WRONG (putting that in caps so people notice it) - the thing is I wired it directly across the relay coil so I didn't have it showing on my original drawing and I only added it for the post but then stupidly I drew it wrong - this is the diode at the top of the drawing - it should go to +12v and not to ground as shown. I'll post a corrected version later when I'm back at my usual PC.
I also just realised - it's not clear from my drawing which end of the blue wire comes from the factory switch and which end goes to motor, and it does matter so I'll change that too.
I love finding ways to put modern features on my older vehicles without spending money LOL
On the Dodge I did another cool mod which fades the cab interior lighting on/off when you open/close the door (like modern stuff does). It's a much more simple circuit I'll try and dig out my sketch and post it.
Van on (even if it's not a van!)
Edit - corrected schematic attached
Last edited by LazySteve; January 12th 2018 12:48 pm. Reason: correction