Im trying to drive a mid 80's vw tachometer originally driven by the coil - terminal.
I am looking at using the relay coil circuit as listed in the ms2 extra hardware manual.
I have read mixed results using this circuit.
all the relays I have opened(mid '80-early '90s vw relays) have an internal resistor of 400-570 ohms in parallel to the coil.
does this resistor need to be cut and removed?
will cutting cause a voltage spike greater than the 160v the 2n5551 and more importantly the Tachometer can handle?
should I go ahead and use something like a 3A 300v ZTX857 NPN instead of the 2n5551?
do newer relays have a internal freewheeling diode?
is this the "issue" that causes some relays to not work?
I have an LCR meter at work and have tested some relays @ 100Hz
high voltage tacho output relay coil parallel resistor/diode
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high voltage tacho output relay coil parallel resistor/diode
v2.2 box, ms2, dual wheel, sequential ignition, staged injection, boost control, maf
'87 VW scirocco, 2L16V, TD0-14T turbo, itbs
'87 VW scirocco, 2L16V, TD0-14T turbo, itbs
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Re: high voltage tacho output relay coil parallel resistor/d
In this case you just want the coil, no resistor or diode. The flyback voltage from the coil is what triggers the tach. A flyback diode will snub out the signal. The tach will be fine. The small relay coil won't generate as much back emf as an ignition coil does. The 160V 2n5551 is enough to handle the spike.
Find the Manuals up top under Quick links: Manuals.
Cheers Luke
Cheers Luke
Re: high voltage tacho output relay coil parallel resistor/d
I'm wondering what the purpose of a resistor across the VW relay coil is? I've never seen that.
Rover SD1 3.5 EFI
MS2 V3
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Re: high voltage tacho output relay coil parallel resistor/d
It does the same job as a diode but not quite as well. Here is a great article on pretty much all things relay. http://www.autoshop101.com/forms/hweb2.pdf
Find the Manuals up top under Quick links: Manuals.
Cheers Luke
Cheers Luke
Re: high voltage tacho output relay coil parallel resistor/d
Not too impressed with that article at a glance - early on it shows the same fuse feeding the entire circuit. Perhaps the main purpose of a relay is to save on wiring etc costs on the low current side.slow_hemi6 wrote:It does the same job as a diode but not quite as well. Here is a great article on pretty much all things relay. http://www.autoshop101.com/forms/hweb2.pdf
That wouldn't be possible if it uses the same fused feed for both - the purpose of a fuse is to protect the wiring.
When such a fundamental is wrong I can't be bothered reading further.
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Re: high voltage tacho output relay coil parallel resistor/d
That cracks me up!!! I work with relay circuits in the automotive repair industry on a daily basis. What you call fundamentally wrong is done on a large scale by the OEMs. What exactly is fundamentally wrong with supplying the field and the load with the same wire being protected by the same fuse? Or maybe I am misunderstanding your post....?DaveEFI wrote:Not too impressed with that article at a glance - early on it shows the same fuse feeding the entire circuit. Perhaps the main purpose of a relay is to save on wiring etc costs on the low current side.slow_hemi6 wrote:It does the same job as a diode but not quite as well. Here is a great article on pretty much all things relay. http://www.autoshop101.com/forms/hweb2.pdf
That wouldn't be possible if it uses the same fused feed for both - the purpose of a fuse is to protect the wiring.
When such a fundamental is wrong I can't be bothered reading further.
Ricky-
1995 Nissan 240sx, 403 LS strokerv8 N/A 6speed trans
MS3&MS3X v.3.0 PCB
42lb/hr Hi-Z inj.,230/232 @.050 on 114LSA cam
sequential fuel and sequential spark
LS3/LSA card MAF sensor
97 Mazda MX5
MS3 2002 vvt motor
.60 trim T4 Turbo at 15 PSI
1995 Nissan 240sx, 403 LS strokerv8 N/A 6speed trans
MS3&MS3X v.3.0 PCB
42lb/hr Hi-Z inj.,230/232 @.050 on 114LSA cam
sequential fuel and sequential spark
LS3/LSA card MAF sensor
97 Mazda MX5
MS3 2002 vvt motor
.60 trim T4 Turbo at 15 PSI
Re: high voltage tacho output relay coil parallel resistor/d
I explained why.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
MS2 V3
EDIS
Tech Edge O2
London UK.