unijacko67
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| posted on 14/6/25 at 10:53 AM |
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Electric Hand brake calliper control
Hi Guys. I'm using some VW Passat b7 electric hand brake rear callipers on my restoration CRX rally car project.
The callipers are really neat, only 2 pin electrical connection so reverse polarity on/off type operation seems obvious, fingers crossed.
Now I understand that oem controllers will have all sorts of features like hill start, potentially re apply pressure after a disc cooling period,
along with fail safes such as not being able to accidently release while parked up and not accidently activated while driving. I'm fairly sure by
the simple use of a few relays and clutch switch etc that I can get what I need to happen.
I'm looking for a controller/relay that stops applying force when it reaches that force via current or load sensor type thing, otherwise ill be
just using the "time off" type relays, maybe set it two 2 seconds and use a momentary type switch to trigger the timer, not ideal but for a
single user "me" id hopefully not keep pressing it and burn out the calliper motors. I'm not after an official set up for a few hundred
quid, hopefully £40 on relays and a switch, I have a few bits kicking about anyway.
So if anyone knows of some "overload" sensing relays or over current, amps relays etc that could work for me "handbrake on" action
that would be great.
Ps I cant find the calliper amps rating, but any help or advice would be good and be useful info, even if this is a guide of how not to do
it....I'm no expert.
It's been a while so treat me gently lol, and thanks....
http://www.kittenkitcar.co.uk
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gremlin1234
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| posted on 14/6/25 at 12:30 PM |
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do you mean something like this
https://cpc.farnell.com/schneider-electric-telemecanique/lrd21/relay-overload-12a-18a/dp/MC02122?st=overload%20relays
they do a range of trip currents as well
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unijacko67
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| posted on 14/6/25 at 01:11 PM |
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Cheers for taking the time to read my question, much appreciated...
Haha, I'm looking for answers not questions sorry lol, chuckling at my lack of electronical knowledge sorry.
That link seems to take me to something that's 600v so again, no idea
I guess I'm after a 12v relay or whatever it would be called that can have an adjustable load/amp/current detection cut off.....
Cheers
http://www.kittenkitcar.co.uk
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Mr Whippy
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| posted on 14/6/25 at 03:14 PM |
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The actual handbrake control modules are about £30 on ebay. Below is link to a good guide on the systems operation which might make things clearer and
show you how to get it operating. Most of these apparently complicated systems actually work with quite simple signals that can be replicated -
Tbh I never knew it moved by a dedicated team of tiny elves, they must have failed cobbler school 
VW handbrake link
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unijacko67
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| posted on 14/6/25 at 04:03 PM |
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Thanks Mr Whippy, the trouble with that control unit is I'd need to replicate all the signals and the voltages that the ecu sent it perhaps, but
if it's all running on 12v and I could get a pin out diagram, ignore the abs bit it could work eh. I'll delve further into it cheers, just
need 6 little elves aswell 🤣
http://www.kittenkitcar.co.uk
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unijacko67
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| posted on 14/6/25 at 04:06 PM |
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I rekon the original control unit will get messages from brake line pressure in the abs unit, so it would know when and when not to turn on and of the
little elf treadmill
[Edited on 14/6/25 by unijacko67]
http://www.kittenkitcar.co.uk
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adithorp
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| posted on 14/6/25 at 06:50 PM |
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This thread might be worth a read...
https://www.locostbuilders.co.uk/viewthread.php?tid=220813
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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unijacko67
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| posted on 14/6/25 at 07:57 PM |
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Thanks adithorp, I've seen this, I'm not sure I'd know how to use the microcontroller, but the last entry on that thread the chap uses
the ehb totally manual. So I'm contemplating using a relay that is activated via a momentary switch, then after a set time, 2 seconds will turn
off, I may need 2 relays, one for brake on and one for brake off. That way I can make the brake off relay only live when the clutch pedal is all the
way down just to stop any unintentionally releases of the brake, I could also make the brake on only function when in neutral or something that makes
it a bit safer...
One of these maybe......
https://ebay.us/m/V3DVhM
http://www.kittenkitcar.co.uk
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SteveWalker
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| posted on 15/6/25 at 10:11 AM |
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I'd use one timer relay for for brake on and one for brake off - rising edge triggered (i.e. timer starts when it sees a signal and continues to
run even if the signal goes away and does not re-trigger if the signal remains present after the timer times out. If your signal is switching to
ground rather than 12V, then you'd need falling edge triggered.
I'd use a centre-off, 3-position, momentary switch to provide the signals to the relays. I'd also wire one relay through the other, so off
overrides on ... you'd not want to be unable to cancel an accidental brake application whilst on the move.
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unijacko67
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| posted on 15/6/25 at 11:10 AM |
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Good call cheers, I've actually bought a 30a on off on momentary, reverse polarity switch, I've bought a couple of the "off timer"
relays, but may not even use them as I intend yet, I think it will evolve quite nicely, with a few other relays. I've watched the video from the
other chaps link who uses his manually and it seems fairly easy to judge the 2 seconds or whatever you feel it needs. "Keep it simple
stupid" keeps popping into the mix.....
Cheers
http://www.kittenkitcar.co.uk
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JAG
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| posted on 16/6/25 at 07:39 AM |
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We've had this conversation previously here: https://www.locostbuilders.co.uk/viewthread.php?tid=220813
It's tricky but do-able.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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coyoteboy
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| posted on 19/6/25 at 12:42 PM |
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Worth noting that the rules on IVA parking brakes require the system operate with ignition off to engage the brake, but not to disengage.
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WesBrooks
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 posted on 21/6/25 at 05:46 PM |
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quote:
Originally posted by coyoteboy
Worth noting that the rules on IVA parking brakes require the system operate with ignition off to engage the brake, but not to disengage.
Impressive you've managed to get onto these forums!
http://doctrucker.wordpress.com
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coyoteboy
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| posted on 22/6/25 at 11:48 AM |
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quote:
Originally posted by WesBrooks
quote:
Originally posted by coyoteboy
Worth noting that the rules on IVA parking brakes require the system operate with ignition off to engage the brake, but not to disengage.
Impressive you've managed to get onto these forums!
I get spare moments from time to time 🤣
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