vas
Well-Known Member
evening again,
following my writeup regarding the VDO Voltmeters in my dash, I have another issue i'd like to address.
Idle speed values on oilpressure and temp are slightly different with 2k rpm values (and I don't mean the obvious one due to higher rpm).
Had this impression, now confirmed having wired my VDO 2bar boost gauge on the bench supply, wired the sender and attached (with a bit of ingenuity and half a dozen adapters and a tee) a bike pump and a 5bar WIKA 62mm gauge.
Pump a bit, say wika says 1.5bar, VDO will say 1.5 at 24V, 1.4 at 20 and 1.6 at 28 (not exact values but you get the idea, that's the scale of error I'm talking about)
Solution would be to isolate and give stabilised voltage to all instruments (bar the voltmeter which really should be reading alternator output voltage...)
Now, if we agree on the above, the obvious Q is why VDO (and judging from other boats and old school cars) hasn't bothered fitting a 24->24V transformer/stabiliser to gauges/senders supply, wouldn't cost more than 10-20euro for the sort of current we're talking about which is silly low. I mean bench supply says that all the gauges I've tried have a current consumption of 6-8mA (each!, so say four gauges less than 50mA...). That's without the warning and dash lighting (but would be easy to keep that on the alternator supply anyway or mess a lot and change them to led, but really wont bother...
A few more points. My VDO gauges are isolated from engine block, so 24V (or whatever as it turns out) goes in the gauge, there's a big resistor/coil/whatever at the back dropping the voltage to circa 11V which is then sent (together with V-) to the sender. Voltage drop on the sender defines the value shown on the needle. Easy really, means that all Voltage "starts" from the dash, hence easy to sort without routing extra cables or messing in the e/r.
The obvious thing for me to do is to get a buck converter (I have a dozen or so in a drawer...) and get everything down to say 24V sharp and be done with.
Any objections?
In case you're worried I'm slowly loosing grip with reality and I'm splitting hairs, I'm finalising the analogue to N2K converters so all these values will also go to the N2K bus and I want them to be as accurate as possible AND as close as possible to the analogue gauges on the lower helm.
Further I don't want to be using lookup tables for the values and want to get the polynomial right and do the calcs in the code. It's easy to shift values and much easier to tune each sender at my converter box with a trimmer.
That's where I first came up with the nearly impossible solution of "correcting" the values output by the senders based on state of battery charge and alternator output. Theoretically easy but turning out not so, hence trying to solve the problem on its roots...
cheers
V.
following my writeup regarding the VDO Voltmeters in my dash, I have another issue i'd like to address.
Idle speed values on oilpressure and temp are slightly different with 2k rpm values (and I don't mean the obvious one due to higher rpm).
Had this impression, now confirmed having wired my VDO 2bar boost gauge on the bench supply, wired the sender and attached (with a bit of ingenuity and half a dozen adapters and a tee) a bike pump and a 5bar WIKA 62mm gauge.
Pump a bit, say wika says 1.5bar, VDO will say 1.5 at 24V, 1.4 at 20 and 1.6 at 28 (not exact values but you get the idea, that's the scale of error I'm talking about)
Solution would be to isolate and give stabilised voltage to all instruments (bar the voltmeter which really should be reading alternator output voltage...)
Now, if we agree on the above, the obvious Q is why VDO (and judging from other boats and old school cars) hasn't bothered fitting a 24->24V transformer/stabiliser to gauges/senders supply, wouldn't cost more than 10-20euro for the sort of current we're talking about which is silly low. I mean bench supply says that all the gauges I've tried have a current consumption of 6-8mA (each!, so say four gauges less than 50mA...). That's without the warning and dash lighting (but would be easy to keep that on the alternator supply anyway or mess a lot and change them to led, but really wont bother...
A few more points. My VDO gauges are isolated from engine block, so 24V (or whatever as it turns out) goes in the gauge, there's a big resistor/coil/whatever at the back dropping the voltage to circa 11V which is then sent (together with V-) to the sender. Voltage drop on the sender defines the value shown on the needle. Easy really, means that all Voltage "starts" from the dash, hence easy to sort without routing extra cables or messing in the e/r.
The obvious thing for me to do is to get a buck converter (I have a dozen or so in a drawer...) and get everything down to say 24V sharp and be done with.
Any objections?
In case you're worried I'm slowly loosing grip with reality and I'm splitting hairs, I'm finalising the analogue to N2K converters so all these values will also go to the N2K bus and I want them to be as accurate as possible AND as close as possible to the analogue gauges on the lower helm.
Further I don't want to be using lookup tables for the values and want to get the polynomial right and do the calcs in the code. It's easy to shift values and much easier to tune each sender at my converter box with a trimmer.
That's where I first came up with the nearly impossible solution of "correcting" the values output by the senders based on state of battery charge and alternator output. Theoretically easy but turning out not so, hence trying to solve the problem on its roots...
cheers
V.
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