![\"\"](\"https:\/\/www.purplemeanie.co.uk\/wp-content\/uploads\/2017\/12\/Driving-to-the-IVA-test-in-the-rain.png\")
<\/a>Since then the wiper fuse has blown a total of 4 times, not a big problem, mainly because I was intrigued as to what was going on and was increasing the fuse size as each new fuse blew. A couple of the times it blew was when I was testing, but it also blew a couple of times when it mattered and I had to drive in the rain with no wipers. But fortunately, I had decided to carry spare fuses after my school-boy-error of not taking any to the IVA test.<\/p>\n\n\n\n Well, of course, the standard response to any fuse failure is to adopt the age old course of action: throw in a bigger fuse and see what happens!<\/p>\n\n\n\n As the fuses kept blowing I\u2019d managed to \u201cdo in\u201d two 10As (factory fitted), two 15As and then finally found that a 20A held. I was still rather in the dark as to what was actually going on though. Was there a current spike that was \u201cjust about\u201d holding with a 20A? Or was it more of a sustained current draw that was within the limits of this 20A… and of course, why do I need a fuse that\u2019s double the factory fit item?<\/p>\n\n\n\n [ Note: the image above has an RDX relay where the standard indicator relay should be – that’s another story but relates to new LED indicators, brake, reversing and fog lights… but that’s another story ]<\/p>\n\n\n\n Now, sticking in a 20A is not quite the bodge-it-and-scarper approach that it would be to use a piece of tin-foil across the fuse terminals… as had been suggested by some, but it was close.<\/p>\n\n\n\n I went through a bunch of possible options that might be causing the problem. Clearly there was too much current being drawn as the wiper motor started. But I couldn\u2019t imagine Caterham fitting a 10A fuse when they knew there was a startup problem with the motor… or could they? Of course this could be a defective motor, or there was some inrush current protection missing from my car.<\/p>\n\n\n\n Other options I thought of mainly revolved around the mechanical linkages getting \u201cbound\u201d and causing a higher than normal stall current in the motor. If that were happening then it would probably happen at some point no matter how long the wipers had been running… i.e. it could bind at a particular point in the cycle but it could take a few cycles before the problem showed itself.<\/p>\n\n\n\n That didn\u2019t seem to be what was happening…. the fuses seemed to all blow when the wipers were first switched on… and more than that, at the very point the wiper switch was flipped. It did catch me out once when I thought that wasn\u2019t the case, but in the end I decided that I had gone from slow-wipe to fast-wipe and the wipers had stopped mementarily in between those modes – so inducing a “start condition”. It seemed to me that if it was a mechanical bind then at some point in the wiper motion there would be a sticky point and the current would increase there. But it doesn\u2019t feel like that\u2019s what\u2019s going on.<\/p>\n\n\n\n Ok, so it\u2019s probably something to do with startup current. But how am I going to see exactly what\u2019s going on. Hmm. A volt-meter or ammeter isn\u2019t going to be able to tell the story at the split second when the wipers start up. I could use an oscilloscope but the only one\u2019s I\u2019ve got are 15+ years old and are not the sleek slim LCD units you can buy these days. I\u2019ve also got some similarly old logic-analyzers that I could have broken out, but they too are bulky and difficult to extract data from to include in this blog. Very Web 1.0.<\/p>\n\n\n\n Bring on the Salaea Logic Pro 16. My modern way of doing oscilloscope and logic analyser work is to use the logic\/analogue PC dongle from Saleae. They come in different sizes, i.e. inputs, speed and colors. I have the 16 channel Pro version in a fetching anodized red.<\/p>\n\n\n\n Salaea can be found at www.saleae.com<\/a>.<\/p>\n\n\n\n The Salaea 16 Pro is an great bit of kit. It plugs into a USB socket on your PC and can deliver up to 500Ms\/s (mega-samples per second) logic acquisition and 50Ms\/s analogue acquisition all from a box that fits in the palm of your hand. Each of the 16 channels can be set to logic or analogue acquisition and the whole thing also takes its power from the USB bus, so only needs a single cable. I only need a single analogue input for this investigation, but nice to have 15 backups!<\/p>\n\n\n\n I think for the higher acquisition rates you need to have a USB 3 port on your computer but for what I needed in this project, USB 2 was going to be fine. It\u2019s also really tiny so hooking it up to a laptop meant that if I wanted to I could \u201cgo mobile\u201d and connect up the rig to the car as I drove around. In the end I didn\u2019t need that, but it was always an option.<\/p>\n\n\n\n On the PC side of things… I\u2019m a Mac sort of person, so I had the Salaea hooked up to a Mac Book Pro. That\u2019s way overkill for what I needed but if I wanted to \u201cgo mobile\u201d I would have broken out an old MacBook Air or something.<\/p>\n\n\n\n Salaea are beta\u2019ing (as I write this in April 2018) a live capture mode too… the current release of software only lets you see results once a capture has run. Again, that\u2019s fine for this project but I\u2019m looking forward to finding other projects where I can use that feature.<\/p>\n\n\n\n That\u2019s the tool sorted, now how do I connect it to the car.<\/p>\n\n\n\n Hmmm… So… I\u2019m looking to get current measurements of the wash-wipe circuit. I either need to put an ammeter type device in series with the circuit or I need a current probe. I don\u2019t have anything I can connect to the Saleae that is like an ammeter or that I could construct… to do that I would need an accurate and low resistance that\u2019s in series with the motor and that I could then measure the voltage drop across. We\u2019re talking about 10 or more amps here so the resistance would have to be very low – or else I\u2019m going to be affecting the measurements by adding more power draw and voltage drop. I didn\u2019t have those sort of components to hand.<\/p>\n\n\n\n My solution was a current probe. I have a 0-20\/0-60Amp dual range current probe that generates a 10mV\/Amp and 100mV\/Amp in it\u2019s two ranges. For a load of less than 20A (my 20A fuse is holding, so I\u2019m interested in less than 20A draw) the lower current range of 100mV per amp should do nicely.<\/p>\n\n\n\n For those not familiar with current probes, they measure the net current flowing through any wires passing through their jaws. The effect is an electromagnetic effect that we won\u2019t go into here. However, the result is that the net current flow produces a proportional voltage response on the probe’s output.<\/p>\n\n\n\n My next problem was that the current probe has a BNC connector on the end. That\u2019s fine for the old-school oscilloscopes but not what the Saleae needs. It uses 1\/10\u201d headers for its input and has breakout leads that can hook up to 1\/10\u201d headers or at a push bare wires. I was unlikely to need the BNC connection type again, so… off with its head!<\/p>\n\n\n\n I could have made a BNC to 1\/10\u201d converter cable, but I was feeling lazy. That being said I also couldn\u2019t just hack off the ends, I did need to at least provide something a little more professional – OCD, moi?!<\/p>\n\n\n\n Back on the Saleae side of things, it\u2019s analogue inputs are configurable up to a maximum input voltage of 3.3v. So, with 20A and 100mV\/A, I need a voltage range of 0-2V – that\u2019s perfect for the Saleae. Bostin!<\/p>\n\n\n\n Now I need to figure out how to get the current probe clamped around the wiper circuit input. Hmmm (again)…<\/p>\n\n\n\n I dangled myself into the passenger side footwell hoping that the wiper motor wires were accessible – they weren\u2019t. The wiper motor is tucked up under the passenger knee panel. Hmm. I could of taken the knee panel off but I was feeling lazy, as discussed above.<\/p>\n\n\n\n What about getting the probe on the back of the fuse panel. That had been the plan all along. But there wasn\u2019t a lot of room there either. I\u2019d probably have to unbolt the fuse panel to be able to get at it. Hmm.<\/p>\n\n\n\n Then came a eureka moment. I\u2019m sure this is something that old hands know all about and use all the time. But I was pleased I worked it out myself… Use… a… modified… fuse (as pictured above).<\/p>\n\n\n\n You\u2019re regular automotive fuse is essentially a plastic molded holder for the fuse wire. My plan was that I could nibble away at the end plastic of a blown fuse and insert a wire loop that I could get the probe onto. It has to be a \u201cblown\u201d fuse or else my wire loop will only be in parallel with the fuse wire and I won\u2019t \u201csee\u201d the full current in my probe. Then, once I have this fuse Frankenstein, I can pop it into the fuse socket for the wipers and attach my probe.<\/p>\n\n\n\n Here\u2019s the modified fuse…<\/p>\n\n\n\n I could probably do a neater job than this second time around if I had another go – but it will do. I had to file away some of my soldered connections so the fuse would fit back into its holder and the wire loop got caught on the soldering iron at one point and so I lost a bit of the insulation – it’ll do!<\/p>\n\n\n\n And I also probably would have got the measurement done faster if I\u2019d have taken the knee panel off… but lazy doesn\u2019t mean lazy in all respects. When there\u2019s a Eureka plan to hatch then lazy goes out of the window!<\/p>\n\n\n\n And here it is in the car with the probe attached.<\/p>\n\n\n\n Now to take some measurements.<\/p>\n\n\n\n After a false start where I actually started to probe the wrong fuse, I finally found the right fuse (it\u2019s tight up in that fuse box), and got to taking some measurements. I set the analyzer to 5ks\/s and the full 3v3 input range. I didn\u2019t need a lot of either time or voltage resolution… I was sure that anything that was going on was happening at the ms (millisecond) scale and not at the nanosecond scale. I was mostly right.<\/p>\n\n\n\n The image above is a screen shot from the Saleae with the probe being connected into the wider fuse socket. The first spike is the ignition being turned on. Then we see a big spike where the wipers are turned on. There are then 8 “bumps” showing the wipers making 8 sweeps (4 cycles of left then right). It’s not totally obvious to me why there’s a spike associated with the ignition switch being activated – though I assume its something to do with the wiper reverse\/park, there’s a momentary energising of the motor as the park circuit decides that the wipers are in deed parked.<\/p>\n\n\n\n But we’re interested in the big spike…<\/p>\n\n\n\n We can see that the initial in-rush spike is large but also drops very quickly only to be followed by a wider almost the same amplitude second wave of current.<\/p>\n\n\n\n<\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a><\/a>