Test Russco SC-120 battery charger. The open circuit voltage will not drop below 91VDC. The manual states 24 - 120, so I think the charger is broken.
Test with a toaster as a load - some electronic outputs 'leak' enough current to fool a digital multimeter into erroneous voltage readings. Adding a load will drop the output down to the actual output of the circuit.
The current meter jumps to 5 amps immediately and the output voltage is still 91 VDC ... so it was not a phantom voltage, or just 'leakage'. Increasing the current (current knob varies from 0 - 100%) raises the voltage to just under 100 VDC. The current should have gone up, but I didn`t see that. One of my battery clips fell off the load and contacted the other battery clip - so it short circuited.
The good news - there is NO SMOKE! I didn't let the 'magic smoke' out of the charger.
The bad news - there was a bad noise from the transformer before I hit the off switch. After separating the output clips again (kept in place with electrical tape, this time) I tried the charger again. No output voltage ... NOTHING ... at ALL ... 0.00VDC. The voltage setting and current setting have no effect. The light is on that shows there is power, but the ammeter does not move.
OK, disconnect the load, the output voltage is still 0 VDC. Check the power switch. It works fine (power light turns off, then back on when I turn the switch on again).
What else can I check? The DC fuse! Remove the fuse and check the resistance. The fuse should blow and protect the rest of the circuit, right? 0.00 ohms (as you would expect a fuse to be). Sigh ... the fuse is OK ... but the charger is broken. How does THAT work?
OK. So I appear to have broken the charger. Well, it wasn`t working anyway, but I broke it some more. Since it has no warranty (I bought it used), I'm going to open it up and see what's inside ... and whether I can fix it!
Before I do anything rash, look to the internet for instructions, troubleshooting, et al. A couple of threads on DIYElectricCars for RUSSCO chargers. It appears that the SC-120 has a couple of specific voltage ranges that it can charge. The 24 - 120VDC that I read is not correct ... great, so it likely was NOT broken when I started! Perhaps the internet search should have been done prior to my testing ...
Look for some video of how to take apart the charger. I find no videos. I find no articles. I found an ebay auction for a schematic of a RUSSCO charger ... but that`s it.
So I guess I`ll muddle along on my own. Let`s start by trying to get into the charger. There are several screws around the unit. There are two access plates that can be removed to access the AC in and some sort of external transformer.
No help there. Terminals are revealed, but nothing else.
Look at the bottom (which is plastic). There appears to be two layers of plastic, but they are glued together. No joy there.
What the heck, you have to start somewhere ... remove some of the screws to try getting it apart. I hear (unfortunately) what sounds like nuts and washers falling inside the charger. And then a clunk, like a transformer has had the last screw removed and is now lying on the bottom of the case ... but that's only a guess ...
No turning back now ... I can't run a charger with washers and nuts rolling around loose inside it. Even if it was working, things need to be bolted down to be safe.
Onward! With every screw removed that makes any sense at all (I did not remove all 4 screws holding the fan cover, or the fan, or the switches and lights) the case does not open. Great. Now what?
The base. There must be screws hidden that attach the base to the charger.
I shone a light from one side, near the bottom, to see if there are screws that go from the bottom plastic into the frame. There are a lot of them. So I locate them (approximately) using light from 2 directions, then drill/bore a hole in the bottom piece of plastic with a phillips screwdriver bit. And I FIND SCREWS! I happily remove them ... and more nuts come off and slide around inside the charger
...
After removing 10 screws and removing the base, I realize that 6 of those screws were for the standoffs of a PC board and the other 4 were ACTUALLY to remove the bottom of the charger.
So now I have a peak inside. There are a handful of nuts and washers. I removed the diode heat sink from the side, the 4 bolts holding the transformer onto the side, 2 screws for the fan, 2 for the fan guard, the previously noted 6 standoffs for the PC Board ... and nothing will come out of the case!
There are wires connecting the various pieces, and the wires have connectors that will come apart. But the PC board is at the bottom and is too wide to tilt and get out of the hole in the bottom of the case. The transformer won`t get by the PC Board. I could remove the diode and it`s heat sink (which has a temperature sensor on it) but that`s about it.
Examine the case ... it appears to be a single piece of metal cut and bent to make a box. The sides do not appear to be welded. The box is painted, but the paint comes off easily at the seams. Various available sizes of screwdrivers will not fit into the seams and force them apart. I NEED to get the PC Board out, so that other things will come out, so that I can power things up and check what, if anything, I killed by shorting out the battery leads.
The PC Board is quite large, but the traces are widely spaced (minimum spacing for 220ish VDC or 120 + 36V boost = 156 VAC * 1.414 = 220.6VDC). Perhaps there is not a lot of control on the board? That`s a bit much to ask.
How would I design a charger? I'd take 120 VAC through the isolation transformer, then a full wave diode bridge. Use a power transistor to drop the voltage to a requested DC bus voltage level dictated by the first dial. Then I'd limit the current from that bus out to the batteries according to the second dial. The charger needs a constant current stage, a constant voltage stage, then a cut-off stage and timeout. That part would be in the micro. Heck - ALL of that is controlled by the micro. The hardware circuit does the diode bridge and switches the transistors when the micro wants them switched.
I can see if a user identifiable component was damaged, and replace it, and get it perhaps to do what it was designed to do. But that`s it. If I want to be able to use a lower voltage, I`m better off to start with an Open Source circuit.
Crap. I messed up a $300 ebay purchase! Oh well, it`s not the first time and it is almost certainly not the last time! I SHOULD have learned a bit more ... $300 is a bit steep to learn that I should do an internet search to find out how people who OWN a charger say it works instead of believing the manual. At least I RTFMed ...
The results:
- the charger will not work for the RRC Electric Motor Module build unless I'm using a 132V or 144V pack.
- the charger no longer works (it may or may not have been broken to start with, but it is broken now)
- fixing this charger is no longer a high priority since it will not work for the near term goal of the RRC build.
So I will pack up the parts, the manual, and a good portion of my pride ... and put it in my wall of shame (storage for items that need repair) to await a time when it becomes the highest priority task.