Add a Tachometer

[ppronti]

Easy:

I 100% agree with you except I’m not sure what you mean by voltage may not be constant at the other end of a wire. But I do believe what I was trying to convey was the same idea. All components of a circuit including connectors, fuses, switches, buttons, and yes you are correct even about wire itself, etc… these things all have resistance, but for the most part, these resistances should be negligible values – if they aren’t negligible, there is a problem – corrosion or something.

If the individual reflects on their electricity class (or even a general introductory class in physics), V=IR (Voltage = Current (Amps) * Resistance (Ohm)). Voltage is a measure of electric potential, or a loss thereof when across a load. In an automotive (or likewise, motorbike) application, Voltage at the battery remains “constant.” Any automotive lamp/horn/speedometer/other load (in the GZ250 diagram we should be messing with) is rated for 12 V. If one is experienced with electrical systems of automobiles, motorcycles, etc., it is generally (if not absolutely) the case that most circuits have their respective loads (resistance) wired in parallel (for example, all lights should see the same battery voltage drop from one side of the load to the other). And automotive parts are generally built robust enough so that corrosion, and any potential-loss effects thereof, is minimized. So practically speaking, one generally should not need to check for small voltage drops in automotive applications, (with exception to finding out if there is corrosion or other circuit discontinuities) – which is why text lamps are available and so widely used – either there is 12 V potential available or there isn’t (an indicator light is on or off).

What does (more often than not) vary when we add/remove components in an automotive application is total current draw.

Any individual load requires a certain current draw. Since V=IR, and V remains constant (and most loads in automotive applications remain fairly constant), when you add a component (like our tachometer), you effectively reduce the value of R because you are adding a path for current to flow (if anyone wants to talk/understand this concept you can look up “parallel circuits” and the “effective/total resistance” thereof or ask here). So then the overall R goes down and thus the current draw goes up. Literally, every load in a parallel circuit requires a certain current draw.

[Water pipe analogy – it’s like taking a 6” pipe, cutting a section out of it, and using two 2” pipes to connect, the “resistance” would be seen at the 2” pipes. Adding another 2” pipe in PARALLEL would increase the amount of water (analogous to the amount of current draw in the electrical circuit) to flow.]

[The following is an example – they are not real numbers] If you have 5 lamps in your running lights system and each requires 1 A of current, total current draw for the five lamps is 5 amps. If we add our tachometer lamp circuit, in parallel (which is what I am offering suggestion to do), the total current draw for the running light circuit is 5.12 A because the tach light requires .12 A. (This current draw would be measured, in line/series, AFTER the “Ignition On” connection for the tach).

Anyway… probably boring people to death… and killing a lot of time… lol…

[Easy Rider]

Originally Posted by ppronti

Easy:

I 100% agree with you except I’m not sure what you mean by voltage may not be constant at the other end of a wire.

Anyway… probably boring people to death… and killing a lot of time… lol…

Yes, methinks you should have stopped at the first paragraph !! :roll:

By the time you reach the end of a wire (or circuit) that is farthest from the battery, the voltage WILL vary a bit depending on how much current you are drawing. The voltage of the battery remains (essentially) constant but the voltage at the far end doesn't.

For most things, that is insignificant BUT for high current devices, like headlights, it is NOT insignificant. Folks have discovered that they can get a little more illumination even from the stock lights by using heavier wire and a relay. That is required for aux. lights that you add because the "engineered" wire, switches, etc. won't handle the additional load, without overheating and making smoke, that is. :shocked:

Thus, a small voltage drop may not mean there is a problem.......if the circuit serves a high current device.

I have forgotten why this specific discussion started so........that is usually a good clue that it is time to let it die !! :biggrin:

[alanmcorcoran]

Hey Paul,

Although I will never use* any of the information you posted I am glad you took the time to do the research and post it. The best thing about the internet is that experts like yourself can choose to share their knowledge and the rest of the world can benefit from it at no cost. As someone that lived most of their life without the Internet, this is a very helpful development!

I have an old 52" DLP TV in my bedroom that I had written off as too expensive to fix until I found step by step instructions on the Internet complete with photos and part numbers. Took me two tries to get the right colorwheel for my model, and I had to nearly completely dismantle the thing to install it, but after less than an hour of screwdriving, I was back in business!

*Not that I think it's wrong: I just don't think a tach is worth the effort. I got one on the Strat but I rarely look at it. I think I know when I need to shift based on the feel/sound of the transmission. Don't think you can redline a GZ and the Strat would have to be doing about 150.

[ppronti]

Alan

My interest in doing the research on this project was actually rooted in the issues I have had with this bike since I have bought it – knowing that the previous owner had confessed (over a not-quite-running-properly bike) that he had opened the bottom of the carburetor. With my technical background I figured, “eh… you’ll figure it out.” So I bought the bike for what, now I realize in hind-site, was more money than I should have offered… it has had a snowball of issues – head gasket blew (just completed that work), chain/sprockets/front brakes are shot (getting parts for those now), and here soon I will be getting on the carb again (as I work on the drive).

So, with a bike that isn’t tuned properly, I bought the service manual and as I also perused the many contributors work on this forum over the past year about the carb, I came across the tach mod and said to myself $50 was an inexpensive way to be able to know what the engine RPM is to be able to tune the bike – and even set the idle speed.

And as I further read the issues with the installation of the unit (horn tone fluctuations, I decided to understand the schematics) – I actually took some photocopies of the schematic from the service manual and a 30 color marker set, and colored-coded the tracings of the wires accordingly – otherwise the schematic was daunting to me (I learned a lot from doing this – if I run into a schematic like this again, I may not need to revert to my Kindergarten-skills!). So really, the motivation in doing the research was selfish.

As I am a technical person, I like having a tach on an engine… it helps troubleshooting in general. I felt the 10ish hours reading the schematic an investment and would eliminate downstream issues in pulling current from the wrong place (didn’t want horn, or any other, fluctuations.

And, since I did the work, and you all have helped me before you knew me (thank you all), I wanted to “give back.”

[burkbuilds]

Great post, lots of helpful info! I bought this tach for my GZ but never installed it. After reading this post, I put it on my Vulcan 500 and it works great! Thanks for the info, even though some things were different, the overall information was a big help. I found the power source from the speedometer light and connected my power leads there, grounded to a grounding terminal under my tank and hooked the green wire up to the negative terminal on one of my coils and it seems to be working accurately! I'm idling at 1250-1300 which is specs for my bike, and I hit 4000 rpms in 6th gear at 55 mph, 5000 rpms at 70 mph. Thanks again for the helpful post!

[whitelightning]

is this the right tachometer for my bike even though it works on twin or single cyl?
http://cgi.ebay.com/ebaymotors/HONDA-KA ... ccessories
asked the seller if this would work on my bike he said............."if your bike is a dual fire ignition system, you hook the tach to the negative terminal on the coil"
what do you think? :??: :??:

[Sarris]

Yeah, that's the one, but it's only $49 here: Tachometer

This is where I purchased mine. Very easy to intall and works perfectly.

[GEREN]

Any issues with dual-fire tachos?
http://cgi.ebay.com/ebaymotors/CHROME-M ... ccessories

[Sarris]

None.

[GEREN]

K. Not questioning anything but wanting to make sure: The one you posted a linked for, Sarris did say single fire on the tach description.
The ones I'd readily have access to say strictly dual-fire V-twin engines only. And another one says they're for Harleys!
Exact same design though.

So there wouldnt be any issues with the above mentioned tach on a GZ250??