If the freedom of speech is taken away then dumb and silent we may be led, like sheep to the slaughter.

- George Washington

Thursday, 5 January 2012

Sparkbright Products Voltage Monitor

I've been meaning to do a post about this for a while, but tomorrow always seemed a good time to do it.

A few months ago, on the advice of someone on an internet forum (yeah, I know) I bought an LED voltage monitor on eBay. The reasoning was this: a couple of years ago, both bikes died on me in the same week. Curiously, for the same reason - a failed regulator/rectifier. The Honda ST1300 died on the lane up to the house after a 50-mile ride (phew) and the Yam failed a diagnostic session with a multimeter after it had only just got me to work and back one day. In both cases, the reg/rec had failed and either no charge or a wildly varying charge was getting to the battery. In both cases, the components were replaced and the bikes ran normally afterwards, without even toasting the batteries. But it occurred to me that I had been lucky, and if this had happened a long way from home I would have been in a right pickle. Early warning of a failure could have prevented a lot of grief.

I started to look for a dial-type voltmeter when someone suggested this indicator LED. It's made by a guy in Glasgow, and everyone on the forum who had bought one raved about it. It's hard to find a place for a dial-type gauge on a bike anyway, so I punted a tenner on one (actually a twenty, cos I bought one for each bike - and I haven't got round to fitting it to the Sprint yet).

Link to the product here. Sparkbright Products shop here.

It's a three-colour LED (red, amber and green) and it displays the bike's system voltage as follows:

Voltage Output
>15.20 Green/Red alternating (over-voltage)
>13.20 Green (charging)
>12.45 Amber (75% plus)
>12.25 Red slow flash (50% approx)
>12.00 Red 2 flashes, repeat
>11.80 Red 3 flashes, repeat
<11.80 Red 4 flashes, repeat

I mounted it on the bike next to the instruments, but (as it is constantly on when running) out of my direct line of sight. This is the position:

And this is the light when it's working (it's red because the engine isn't running and the battery is half-dead after a lot of circuit testing):

When I fitted it, I just fastened it to the clocks with insulating tape and pushed the wires into a switched live and the indicator earth - a temporary arrangement to see if it would work. It did.

In fact, it is very reassuring. It stays green for 99% of the time, and shows amber for a couple of seconds every so often. So I am in the golden 13-15V area for most of the time, and the voltage dips into the 12V area occasionally. I anticipated that this might happen, as the connections to the bike's electrics are hardly robust and may well be a bit flaky. And, let's face it, the XT is a shed - 99% good is 50% better than I have the right to expect. But the key thing for me was that it stayed green even with the lights on. It's an old-skool thing, from the days of dynamos, but I always have the sneaking suspicion that having the lights on is draining the battery. It isn't.

Today, I have been checking all the wiring and the earths on the XT to try to locate an intermittent and peculiar fault, and I decided to make an honest component of it and wire it in permanently while the tank and the plastics were off. A longer earth wire was soldered on and connected to the battery negative, and I used a Scotchlok (yeah, I know) to tap into a switched live at the ignition switch.

All seems well, although a true test will be the commute to work tomorrow night. Will it stay green all the way? Watch this space. In fact, I suspect it has already proved itself. On the two journeys between home and work before the intermittent fault appeared, it was going to amber far more often then usual, indicating that the voltage is dropping lower than it should. The bike's performance remains the same with no cause for concern, but perhaps this little device was giving me an early warning of trouble?

As far as the product itself goes, I would recommend it wholeheartedly. It's well-made, robust and waterproof, and the wires to connect it are neatly tinned. It seems to work perfectly. Running along with the light showing green is reassuring, and (hopefully) I will know about any charging problems before they leave me by the side of the road. The maker, Dr Andrew Ferguson, is a helpful guy, and his communication is personal and friendly. I will probably fit one to every bike I own from now on, as a tenner is not much to pay for peace of mind. The only thing I would do differently is that next time I will get a smaller unit. The 10mm standard bulb is a bit too big for something that is on all the time, when all you need is a speck of light in the corner of your eye. When I mount the other one to the Sprint, I will be careful to mount it well out of my line of sight, as it can be distracting, especially at night. Next time, I will probably go for the 5mm version.

Highly recommended.


  1. That's a pretty damn cool gizmo. Especially as a serial Honda (routine failure of reg/recs) and Suzuki (routine failure of all electrics) owner.

    Thanks for the heads-up and the link.

  2. Way back in the mists of time, I had a home-made voltage monitor in a Mk 2 Cortina. It started dipping into the red, then stayed in the red.

    I thought well, it's home-made, it's probably gone conkers on me.

    Nope. The car died with a knackered dynamo (yes, it was that old) and I got my money's worth out of the AA.

    So if yours is suggesting problems, check out your charging system. Could save you a long wait in the cold.

  3. Endo, I know it's a well-known Honda problem, but every brand-specific forum that I have visited abounds with remarks like "yeah, it's a common issue with Suzukis/Ducatis/Brough Superiors/whatever". I think the reg/recs they fit to bikes are not up to the environment. I've never had one fail on a car, although the design is different, being built into the alternator (mind you, so was the Honda's ...) Well worth the bucks, but I would go for a small one next time.

    Leg-Iron, thanks for the warning, although I am reasonably sure the charging system is AOK. Voltages at various phases of the moon are as they should be. The problem is intermittent, with the engine occasionally cutting out when I switch the lights on - and then not doing to 30 sec later. I suspect a bad earth somewhere, with the CDI unit earthing itself through the nearest route available. All done and ready for a test later today. If it's still there, then it's probably the reg/rec AGAIN.

  4. Richard

    Excellent and very timely - I was just about to buy one of these Clearwater Sentry things from the USA:


    I discovered the battery flat on Mrs N's BMW F650GS over Christmas (another story of hyped up expensive Odyssey batteries). Then it struck me that with the magneto type alternator there is no "battery light" to show no charging.

    Hope to see you soon - I'm planning a weekend in Wales soonish...

  5. That looks a nice product, although I reckon the Sparkbright one will do the same for a quarter of the cost.

    Drop me an email when you're thinking of coming over this way and I can let you know when I am free of work commitments, swap mobile numbers and so on. Be good to meet up.

  6. Looks a good idea, BUT I would question the voltages a bit. It's rather difficult to determine the state of charge in a lead acid battery solely by voltage. A hydrometer is the best method, but not easy with many so called "sealed" batteries. Fully charged and left to stand, a new one should read around 12.8 volts. Anything below this indicates that it's less than fully charged, or in the case of an older battery, that it's, er, getting old!

    So it follows that when the engine is running less than 12.8 means it's not being properly charged. Once down to 12 volts you are looking at walking home in the near future... Most modern alternators regulate at between 14.3 and 14.7 volts - the higher figure tends to be needed for the latest types of batteries. Much above this will lead to gassing and premature failure of the battery.

    I would compare readings taken at the battery with a digital meter, and the colours/flashing indications of your monitor, then you know for sure when the battery is being charged.

    Cars usually have large enough alternators that under most situations they will maintain full voltage, except possibly whilst idling. Smaller bikes, on the other hand, may need reasonably high revs to get full output, and could take some time to get a partially flat battery back up to scratch.

    You also need to allow for voltage drop in the wiring harness and switchgear, so the best place to measure is directly on the battery terminals. Obviously this isn't practical with something like your unit, but so long as you see a definite change in voltage when the engine's running you should be OK.

    I have one of these on my Fiat Panda - since I have a dual output alternator, and second battery, it's very handy to keep a check on what's going on. Connected to a changeover switch I can select either battery, and by comparing the relative voltages, see what the state of charge is in the second battery. Unfortunately it doesn't have any provision for illumination, but at night I can tell by the headlights if something's wrong.

    "Knackered dynamo" - yes, Leg Iron, I'm also old enough to remember them (Lucas C40 on the Mk1 Mini, IIRC). My CZ/Jawa 175 had a 6 volt dynamo, which struggled with the Cibie halogen headlight I fitted...

  7. "I have one of these on my Fiat Panda"

    Your "embedded" links don't show too well, so here's the URL if you didn't spot it:

  8. I don't think the purpose of the monitor is to report on battery condition (although I remember voltmeters in cars being wrongly called 'battery condition indicators'). It's just a real-time indicator of the state of the charging system. I will certainly check the LED colours against a multimeter on the battery, out of interest. But all I need to know is 'is the battery getting a decent charge?'

    The monitor is now wired as close to the battery as possible consistent with a switched live feed - black direct to battery negative, and red to a point immediately after the ignition switch. Combined with cleaning up all the earths, I now get a solid green light at all times when the engine is running, even at idel with the lights full on. That reassures me that the charging system is healthy.

    Incidentally, I am familiar with second batteries in caravans, and on winch-equipped 4x4s, but why in a Fiat Panda? Seems like overkill :)

  9. "I now get a solid green light at all times when the engine is running"

    Yes, that's fine. I just felt some of those values were a little bit off the mark.

    "but why in a Fiat Panda? Seems like overkill :)"

    To power a 1kw 230 volt inverter, which allows me to operate lights & power tools if I'm working out of reach of a mains supply. I can also have a brew-up without needing to carry a gas stove! And in summer I have a 12 volt fridge for drinks etc.

  10. A man after my own heart - a free-range power supply.

  11. "A free-range power supply"

    It often gets used in my friends chicken sheds during flock changeover & maintenance periods....

    One advantage of an older car is its complete lack of high-tech (apart from a simple electronic ignition system*), so I use it as a mobile test bed for my ideas!

    *I have a points type distributor under the seat, which only takes a few minutes to fit, if needed. I can run the ignition from either battery, so even if the alternator packs up the fuel will run out first. I have a "party trick" of leaving the engine running whilst taking the key out, and locking the doors...

  12. Spare battery, spare distributor, and I would imagine a full toolkit including pullers, sockets, torque wrench ... it's either a Fiat or my old Triumph Dolomite. Never went a mile from the house without enough for a full overhaul in the boot.


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