slowing down current?

Hi All
I picked up a digital voltage gauge for my families Polaris Ranger. **broken link removed**

Tested it on a battery first, fine, drilled a big hole in the dash, installed, started up the ranger, and the gauge goes NUTS. It's very hard to read...it's like it is reading to fast. It's in two digits and once decimal, 12.6 for example, the .6 is fluctuating to fast to to read, the 12 is flickering too.

Well tossin it and grabbing another is no fun, so I'm trying to fix it. The only thing I could figure to do with my internet education is to wire in a capacitor, because those are supposed to filter too?
So I loaded up the kids and went to the local Radio Shack.

I bought a couple of capacitors, one is a 1uF non-polarized Electrolytic Capacitor and the other was a 10UF. I hooked them up and the guage won't work at all with them. What am I missing here? Is the gauge not enough load to trip the capacitors? Am I thinking on the right lines?

It looks like the meter is probably working fine but the voltage you are measuring has a lot of noise on it. This kind of meter works by sampling the voltage several times per second and what it's doing is sometimes seeing low noise and sometimes spikes on the supply.

There are two solutions, one is to wire it directly to the battery terminals which is the lowest noise point in the vehicle although I can't see a power switch on it so that may not be an option. The other is to filter out the noise as it reaches the meter. To do this you really need a bigger capacitor than the ones you have, at least 100uF and preferably 1000uF and they should be rated at least to 35V. Observe the correct polarity or you will get a nasty bang! Don't assume that because the battery is 12V there are no voltages higher than that, lots of vehicle electrics produce spikes on the supply which are far higher. Wire the capacitor directly across the meter wires, do not rely on nearby metal to be a good chassis connection. That will go a long way to stabilizing the reading but if it still jumps around, try wiring a choke in the positive wire, the capacitor must be on the meter side of the choke. Look for values higher than about 10mH, if you can't find anything suitable, get a small audio output transformer and use the wires going to it's primary winding. Leave the secondary unconnected.

Brian.

chassis connection?
Do I need to ground the capacitor?
These things have axial leads, one in and one out. I just hooked it up inline of the 12v lead coming in to it.

That's not how it works. The capacitor acts like a local reservoir, it absorbs energy quickly and releases it slowly so the overall effect is to make the voltage across it less quick to change. The capacitor has to be wires ACROSS the meter wires and it should be physically directly across the wires. What I meant by avoiding a chassis connection is that you shouldn't assume the whole chassis is at the same voltage, if you just wired the capacitor negative to the nearest chassis point you might actually feed more interference in to the meter and make matters worse. The voltage is measured between the wires so that's where you want to keep it stable. Be careful to wire the capacitor the right way around, red wire = '+', black wire = '-'.

Brian.

o jeez
man I have got things screwed up.

Well I just T tapped this thing into a hot that comes to life with the key, my radio power on is on it, as well as the sensing wire for my winch.
The ground I just t tapped into a chasis ground in there that everything else is on.

Well you are saying to wire in a 1000 uf capictor between the hot and ground on the leads going to the volt gauge? Will that mess up anything else that is tied in on this the positive side of this wiring?

Nothing will mess up. In fact, even a 1000uF capacitor is insignificant in the grand scheme of vehicle electrics.

Yes, hook the capacitor across the wires going to the guage. It should improve matters straight away but if not, you need even more filtering and the choke I mentioned earlier is the best solution. It should look something like this, forgive the lack of a real picture!

A series inductor will block/filter HF noise (ignition signals)

Series inductor = a choke :roll:

Brian.

will it hurt anything if I wire up the 10uf that I already have in there?

Radioshack is about 7 miles away and the kids are napping.....

It wont hurt anything but I doubt it would be sufficient to see much improvement. Larger values have greater ability to absorb and release energy so they 'level out' the voltage better. 10uF is a very small value and although it's a step in the right direction, it's a very tiny one. Consider that the 1000uF I suggested has 100 times more storage and even that might need the choke (oops... series inductor) to assist it.

You're lucky, my nearest Radio Shack is 100 miles away !!

Brian.

No it will not hurt but increase the capacitance to a few 100 uF and use a 10 nF polyester in parallel to the electrolytic one ; because electrolytic capacitors becomes inductive at high frequencies due to the construction

Ok well I got mom to come and watch the sleeping kid.....the other one and I darted to the store and just made it 10 minutes before closing.

They didn't have any 1000UF so I went with a 2200uf.

Also I changed the way the gauge was wired up to hooking it up straight to the battery.

Rigged the 2200uf capictor as shown above and it is still squirly, the last digit is unreadable.

I'm about out of patience on this one, this stupid gauge.

I appreciate the responses. If you want some capacitors give me your address and I'll mail them to you.

---------- Post added at 23:17 ---------- Previous post was at 23:15 ----------

2200µF 50V 20% Axial-Lead Electrolytic Capacitor - RadioShack.com
was what I used

Looks like you did all the right things. It's normal for the last digit to change up or down by one count but it shouldn't happen that rapidly. There will always be rounding errors, for example if the voltage is 12.55 should it show it as 12.5 or 12.6 so it might flicker between the two. A good meter should show the average of several measurements, especially when designed to work in a relatively hostile environment like a vehicle so the updating should be fairly slow, maybe two or three times a second. I'm working on a project that uses the average of 2,500 measurements to eliminate noise but it looks like yours uses every single reading.

If you are adventurous you could open and modify it but a degree of electronic knowledge would be a prerequisite.

Brian.

A digital voltage gauge with flickering display is just a bad design. Good ADCs with 7 segment display are available since decades, offering convenient 2-3 readings per second, e.g. using ICL7107. Sounds like someone has re-invented the square wheel. Or setup a wrong oscillator frequency.

There’s a new trend in the market, they use microcontrollers to make all the measurements and display it on the LEDs. Cheap ''voltmeter'' circuits are sold on eBay for few bucks using for example Samsung's SAM88RCRI family of 8-bit single-chip CMOS microcontrollers, that allow simultaneous measurements of multiple voltages using few additional components.

On topic

If ''the choke solution'' it’s too complicated, let’s try to add a resistor in series (red wire) and keep the capacitor in place. Estimated value may start from 10 ohms up to 22 ohms.
If there’s no success and he decide to go further to open the box, he can take some PCB photos, post it here and maybe with a little help to solve this problem. :grin:

i think the circuitry in this thing is way to sensitive

I've got another guage on order. I hated to do that but with the 2200 capacitor in place I really didn't see much improvement.

The thing was like $15. The new one that is on the way is $20. Hopefully it is better.