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Author: Subject: Power Distribution Module Question
John Bonnett

posted on 23/5/21 at 11:57 AM Reply With Quote
Power Distribution Module Question

On the face of it, when wiring from scratch, a PDM is the way forward rendering fuses and relays obsolete and reducing the amount of cable. Motogadget do a nice unit for bikes for about a hundred quid but with insufficient inputs and outputs for a road car.

So a couple of questions.

Is there a suitable unit available for reasonable money? I'm talking sub £1k and preferably sub half that?

Has anyone on here used one?

Any comments please?

Thank you.

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posted on 23/5/21 at 12:44 PM Reply With Quote
Seen the Motogadget one and wondered if using two is feasible. Alternative is Simtek but not cheap.

"A witty saying proves nothing" Voltaire

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John Bonnett

posted on 23/5/21 at 02:39 PM Reply With Quote
Thank you Adi, interesting reading and definitely the future. Unfortunately, well outside my budget so it looks like I'll have to tread the traditional path of relays switches and loads of wire.
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posted on 23/5/21 at 02:59 PM Reply With Quote
Funny isn't it. I keep thinking of making my own one of these, but there's one over-riding reason not to. On the road repairs. If your relay fails, or your fuse blows, you pop into Halfords and grab another, or ram a nail in it after some investigation. If your PDM fails (as I had on a Megane) - you're buggered, and sending it off for £100s of quids worth of repairs by a specialist.

It's mad. Old clicky, spade terminal parts with huge amounts of bulk, but still seem preferable over something small and reprogrammable!

Report your local potholes, it actually works!

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posted on 23/5/21 at 05:22 PM Reply With Quote
I know AB Performance used the mo.unit blue to rewire a Caterham not long before they shut down. I always thought it looked about right for a kitcar. What do you need that it hasn't got?
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posted on 27/9/21 at 04:15 PM Reply With Quote
I know this is a bit of an old thread but it is exactly what I'm looking for at the moment. I'm thinking of a hybrid of some kind with most controlled by this unit and a few relays for the high powered stuff. I'd love it all to be controlled by one PDU but the car ones with more channels seem stupid expensive.

I'm hoping all of my lighting can be powered by this motogadget mo.unit which should do away with flasher relays and give an alarm/immobiliser of sorts which I believe is an IVA requirement. All switch wires can be switched to ground with fine wires so no need to feed full current through switches which will save on heavier gauge wire.

The Motogadget has the following outputs:

Left turn signal
Right turn signal

The starter looks like it is 30A so probably not beefy enough for a car starter but you could certainly use that to trigger a relay
Doesn't look like there is anything for sidelights but one of the aux channels can be used for that.
Fuel pump can be powered on by ECU via a relay too.
Fan can be controlled by ECU via a relay too.
ECU could be powered by the other aux channel or ignition channel.

Having never done this before, is there any glaringly obviously things I'm overlooking?

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posted on 27/9/21 at 04:44 PM Reply With Quote
I measured a Zetec starter solenoid at around 10a with a higher initial spike. So the 30a supply should be fine.

Iíve bought the motogadget M lock for 7 itís a nice toy.

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John Bonnett

posted on 27/9/21 at 05:30 PM Reply With Quote
This is something I'm really interested in but at the moment I'm out of my depth and would appreciate your experience. Buying two would give 20 channels which would provide enough circuits I would have thought. But just to take the windscreen wipers as an example normally there are two speeds and an intermittent which I believe is achieved with a timer relay. How can that be catered for by a PDM?

Apologies for my lack of knowledge and thank you in advance for help and advice.

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posted on 27/9/21 at 09:01 PM Reply With Quote
This is new to me too so no experience. If I do make something of this route I'll get in touch and let you know but I'm not going to be using windscreen wipers as there'll be no windscreen.

From what I've seen on YouTube and what I've read in the manual, it looks like each channel is quite dedicated to its use so a second unit may not do what you'd like it to.

I haven't really looked too much into them yet but there is a place that do PDM's called hardwire-electronics. Just stumbled across them while googling wiper control on PDMs. There seems to be a lot more control with these, bit more expensive though.

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posted on 11/10/21 at 10:40 AM Reply With Quote
I thought this link may be useful:

Looks like they're also using an MSD 4 way solid state relay block too which would deal with the higher current stuff.

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posted on 21/10/21 at 09:00 AM Reply With Quote
I've now bought one of these so I'm in a better position now to describe the limitations if you are using this one a car.

Obviously this thing was designed for a motorbike so some of the push button inputs won't really translate to a cars.

First thing, you are restricted on the input setup. You can't specifically say this input is toggle switch and this input is a push switch, there are "profiles", of which, the Japanese bike profile closest fits a car as the indicators are toggle type and the headlights are switch and not pushbutton.

Most of the channels will work well. As soon as the device is unlocked by way of either 12v on the lock input (check out the mo.lock as mentioned earlier on this thread. Would work brilliantly with this) or a Bluetooth phone connecting to it, the ignition channel output is turned on. You can also set aux 1 and aux 2 to both come on with ignition, with engine start or with push or toggle switch input so these channels are versatile. Aux 2 even allows for a fan delay so the fan keeps going after the car is turned off.

Ground the "start" input and the "start" output turns on until the switch is no longer grounded. Perfect for started motor.

Brake light and horn both act as push button so as long as the input is grounded, the output will be on. Again perfect for these uses.

The problem I see comes from the indicators and the lights. The indicators do work well as indicators. You ground the left signal input, left output turns on and incorporates the flash (load independent so you can use LED lights without resistors). You also have the option for what they call M-Wave where the indicator pulses on and off with some modulation which is nice. The problem is hazards. They are not available when the key is not in the ignition. You can start the hazards and take the key out and the hazards will continue but you can't turn them on initially without the unit in an "unlocked" state. I suspect this would be an IVA fail. Should be an easy fix, wire a Mo.Flash unit from permanent live to the indicators via a hazard switch. That way the Mo.Unit does the indicating by grounding the left or right input via indicator stalk and the hazard flashing is dealt with by the Mo.Flash unit on the output circuit. You could also not use the Mo.Unit for the indicators and just use the Mo.Flash for all of it. I'm starting to sound like a Moto Gadget advert!

The next problem is the lights, as described in the link on my post above. There is one ground input for the lights and this needs to do light on, light off, low beam, high beam and position/running lights. With the push button they do this by pressing the button to turn on the light, tapping the button to flash, holding the button a bit longer to flip between high and low and another sequence to turn them off. Obviously not suited to a car at all. The other option when the "Japanese" profile is set is basically a flip between high beam and low beam. You ground the "light" input and the low beam output flips to the high beam output. You unground the input and the light moves back to low beam. With this option, the low beam output turns on with ignition and remains on until you turn the whole unit off which would then mean you need to have a switch on the live current side which is no biggy really and should still work, but then you have sidelights and fog lights. These have no dedicated outputs and I believe it is an IVA requirement for the side lights to be able to be turned on without a key in the ignition. I did read the IVA manual regarding this and I noted you don't need parking lights on a vehicle 6m or less but side or position lights are mandatory. There is no mention that side or position lights must be available with the key out of the ignition but I've read in here the testers think differently.

The way I plan to work around this is with a VW headlight switch. These take both a permanent battery live and an ignition live and output sidelights, low beam and fog lights with a handy switch which means you have to turn the fog lights off when you turn the lights off thus satisfying the IVA requirement that your fogs go off with your lights and do not come back on when you turn the lights back on. The permanent battery live powers sidelights and the ignition live powers the headlights and fog lights. This is perfect except for one problem. If the fogs are powered off the Mo.Unit's low beam output which is now basically an ignition live, that current would go as soon as you put the high beams on and the output flips to high beam which would turn off both low beam lights and fogs so this would be an IVA fail. Luckily there is a workaround introduced with more recent firmware on the Mo.Unit. This is called hyperbeam. Basically the low beam output stays on when the high beam output is selected. This fixes the problem of the fogs going off when you switch to high beam but introduces another problem. A typical H4 bulb will burn up if both filaments are lit.

So far I see two ways out of this. Do not use the high beam output and switch on the mo.unit and go with a more traditional headlight switch which will use the same input for low and high beam and flip between them. Or go with a set of dual Photon headlights so you can keep the dipped beam and high beam on at the same time.

All in all, I'm pretty chuffed with this unit. I think it'll do everything I want it to do with a couple of workarounds. I'll have no mechanical relays, only a few fuses, no key only a phone or RFID tag, all electrics are totally immobilised until the unit is unlocked, it is about the size of a credit card, it also has a built in alarm which senses changes in angle so you can set an alarm to go off if somebody is trying to nick your car and put it on a trailer.

Long post I know but hopefully gives a bit of relevent info.

[Edited on 21/10/21 by felix_kentish]

[Edited on 21/10/21 by felix_kentish]

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