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Japanese 05 CVT
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Discussion Starter #41
Here are some components I've used that will help the DIY builder. You'll find all these on eBay. As with most things on eBay, if you can wait for the long delivery time from China, everything is cheaper.

A genuine Arduino "Genuino" Uno will be about £15. Chinese Arduino Uno clones can be had for £4-£5 delivered with a USB cable. I haven't tried one yet but I probably will. Watch out if you specifically want a genuine one, because the wording is sometimes a bit ambiguous on eBay listings. £4.30 delivered from China example:
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I soldered up an input/output board out of stripboard and PCB screwdown terminals. I find it's way more flexible using screwdown terminals than soldering wires straight in the board. Turns out you don't need to make one - you can buy them for £2-£6 depending on the type. They're called Screw Shields.

This one +£2 if bought with the Chinese Arduino above:
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This type is two separate boards for either side, £2.39 delivered from China, with nice wobbly looking soldering:
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This one £5.99 from a local (UK) seller and comes with connection pins which you can't see:
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A bumper case makes it easier to mount the Arduino in something and the open top lets you stack up the shield boards if you want. These ones £2.49 from a local seller:

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I've also changed my fan for a 5V 0.15A USB-powered one. About £5 delivered for this one from a local seller, but cheaper if you can wait for one from China:
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I paid way over the odds for my SSR modules. Here's an example of a 4-relay version of mine with the same relays for £10.79, which is less than I paid for one of my modules. Fewer wires to wire in, too, as they all share the same +5V power line. They come in 1, 2, 4 and 8-relay versions:
88554
 

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I really enjoyed this thread and thanks for going the extra mile to explain things and show where to get them. Glad i could be of service even if for a small bit of code.

I must add if anyone were inclined to get into any arduino's that cheaper ones, like Jonny mentioned, are out there but i must implore you to grab a random "led blink code" and attempt to upload that code immediately to test if the arduino is good. I have dealt with non-genuine (almost always china made) arduinos and have dealt with numerous DOA arduinos. An insane amount actually. So while its viable just beware!

Still anxious to see how you encase your final product Jonny. Good job again on all of this!
 

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Japanese 05 CVT
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Discussion Starter #43
Still waiting for my Arduino bumper case to arrive in the post before I can proceed to final build. I've fitted the fan on the case and tested it with the resistor heatsink and the flow is good, in fact unexpectedly good for a low power fan and the compromised position of the heatsink.

In the meantime, I've got a little ahead of myself and modified my RB Batteries charger so it can be triggered by the Arduino. The idea is I can automate the charger as well as the discharger and essentially let it sit there and cycle the battery automatically.

Inside the charger is just a 12V PSU and two constant current LED drivers, like you'd make with a simple home-made grid charger. I made up a little extension board for the 5V relay unit with a 5V regulator, powered by the 12V PSU, which switches the LED drivers on and off. I also made up a trigger line to connect between the relay and the Arduino so it can turn the charger on and off.

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On the charger case I also added a switch so I can switch between triggered mode and manual charging.

If you do this too, make sure your relay unit is trigger HIGH, ie +5V turns the relay on. Mine is trigger LOW, so 0V turns the relay on. It still works, it's just a bit more faff to set up and you have to be more careful with stray voltages when you switch things on.
 

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Discussion Starter #44 (Edited)
Ok, here we go. This was a proper squash and a squeeze. I probably won't use a PSU case again for this sort of thing, it's a bit too small for a DIY project!

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Arduino is at the back behind that mess of wires. 90° USB lead stuck in the side. Then the two SSR relay modules in a small plastic case in the middle. The resistors are on the back of the heatsink. Values are now 500R for the lower rate discharge and a 250R switching in for the higher rate discharge. 120mm fan in the top of the case has been replaced with the 5V USB fan. A blob of hot-melt stops the LEDS wiggling around.

I couldn't fit the voltmeter in so it's temporarily on a flying lead. The other leads are the USB to run it (it can run on a laptop or just on a USB phone charger), output plug to IMA battery, input plug from charger, charger trigger line.

With the case closed:

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Printed some Dymo labels for the front:

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I added in a test point on the front panel where I can either measure the 0-5V voltage range on the potential divider, or put 0-5V on it for testing the box.

See I've also got a 'charge' LED in the panel. The circuit works but I haven't managed to make this trigger the charger satisfactorily by itself when fully wired in. I don't really like the 'low trigger' relay board as a concept here, because it means when the relay is disconnected there is always a stray +5V floating on on the wire which needs to be tied low with a resistor. It also makes me quite nervous that stray static or poor grounding might trigger it, so I'm going to swap it out for a relay that triggers high since it's controlling mains voltage and puts out 200V DC. I don't feel like it's safe. At least with a trigger high relay it won't turn anything on unless you put +5V on it.

So. If I did this again what would I do differently?
1) I'd use a larger case so everything can lay flat. Upright like this means it all fits but I have to assemble it in a particular order, it's REALLY fiddly and the wires all have to be quite short else they won't go in. Having to mount things in the lid is also a nuisance.
2) A case with thicker metal would be easier to work with, too, preferably aluminium or even plastic instead of steel.
3) I underestimated the number of wires and it could do with a lot more screwdown terminals, particularly +5V and 0V points. Using a 2x relay board instead of two singles would mean one less 5V and 0V connection - worth thinking about that sort of thing in advance.
4) Trigger high relays. It's just safer because they stay off no matter what.
5) External reset button would be useful. I will probably add one next time I've got it apart because there's not enough space to get to the pins now it's assembled.
Edit: 6) Longer leads. Longer leads are your friend.

Next job is to modify V3.1 of the code so it doesn't spit out quite as much data, but this is just a tweak.
 

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Discussion Starter #46 (Edited)
Working update. Most of this is not relevant for anyone building just a discharger as it relates to the possible future charger connection and automation. For the discharger bit, I contacted RB Batteries to find out what fuse was fitted to their battery harness to check I’m not drawing too much current, and it’s a 2A fast blow 3AG 1-1/4 x 1/4 fuse. I’m drawing about 1A at max discharge. All fine. Just putting that there for reference.

I pulled the discharger apart the other night to re-work the charger relay trigger wires. Previously it was a single switched 5V/0V line from the Arduino and the relay was powered by the 12V PSU in the charger, all on a common ground. This worked on the bench but was problematic when fully connected up. I swapped it to a dedicated set of 0V/5V/trigger lines directly powered by the 5V power from the USB line. This had the additional benefit of making it a lot harder to accidentally trigger it and it can be easily swapped between high or low trigger in the software. I have a high trigger relay module in the post.

As is typical, the wires I needed to change were right at the back:

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Then I was working through a hole, looking down the screwdriver shaft:

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Also re-wired the charger relay and changed the wiring on the manual/trigger mode switch. That done, wrote a bit of software to just cycle the outputs and the relay fired each time as expected. However, with the mains supply connected, the relay started sticking on occasionally...

Not 100% sure what the problem is yet. The relay is rated to 250V and 10A, probably optimistic for a small Chinese relay, but I’m drawing maybe 1A max. It could be a surge at power-on. It could be a back emf on switch-off, so it might need a resistor-capacitor snubber across the terminals. I have some high voltage capacitors in the loft I can try for this. It could of course just be a faulty relay. I have another one coming anyway so I’ll try that as well.
 
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