Homebrew, open source, repurposed, hacked, software defined, open hardware

Thursday, 9 June 2011

Fixing the OzRoll roller shutter controllers once and for all

To summarise, OzRoll (TM) make a pretty solid and nice roller shutter, which we wanted in our bushfire prone and cold location.

The roller shutter controller which comes with the roller shutters uses an ATMega to monitor for key presses, raise and lower the roller shutter, decide when the roller shutter has finished moving, and, decide when and for how long the NiMH battery pack needs charging.

Unfortunately, the NiMH battery packs seem to die fairly easily, and we had four or so dead on arrival, as the roller shutters were installed some time before the house was ready to move into. Googling revealed multiple sources of replacement packs for about AUD$80. Ouch.

An early enquiry made to the installer revealed that OzRoll, the local manufacturer, had said that after 6 months or so, the batteries were out of warranty, so tough luck.

Disassembly of some of the roller shutters was undertaken to exclude mechanical causes for excessive motor current requirements.

The front panel was removed by drilling out four rivets. No dead rodents or invertebrates of note, even after lowering!

The roller shutter axle was easily dismounted from the motor and opposite spindle.

The physical build was very good. I couldn't fault the engineering. The motor was nice and solid looking, and the power cable inlet appeared to be fairly well sealed.

Continuous power to the nominally 12V DC motor was met with continuous rotation.

Testing found that the instantaneous turn on current when initiating movement - with the roller shutter disconnected from the motor! - was as much as 4 amps. So, even a partly cactus 1500mAH battery pack was going to struggle.

The roller shutter motor, it turns out, has no start or stop switches, and the controller's ATMega was smart enough to be able rely on a sudden increase in current from the power supply to determine if the roller shutter has finished moving.

I suspect the flashing red LED (D8) on the roller shutter controllers saying they needed charging kicked in at some point and gradually drained the batteries in the roller shutter controllers until they were dead.

There is a position on the circuit board for a small on off switch has been bridged with a very puny wire link in all the controllers - who knows, this simple switch may have saved four or five NiMH battery packs from dying, and who knows how many others in other customers' roller shutters that are now in land fill.

I made a subsequent call to the manufacturer, leaving a message asking about replacement battery packs, but was never called back.

Unfortunately, the charging algorithm in the controller seems a bit broken, and allows ongoing charging with about 160mA for a predefined period. It does not seem to turn off when a certain voltage is reached in the battery pack, or care about the battery pack temperature. This would probably explain why the battery packs get so darned hot with charging. I would have thought with such a capable microcontroller, they could have done a bit better with the charging algorithm

I was reluctant to spend another AUD $400 to get battery packs which would eventually die in service as a result of slightly brain dead charging and excessive current demands.

Anyway, a few minutes with a soldering iron, some cable, a solder lug and a DC barrel connector and you'll be able to run the the controller off an external SLA battery. If you cut the circuit board track going to the LED (D8) which flashes when the controller wants to charge battery, you won't be annoyed by the ATMega's complaining about its inability to initiate a charging routine.

I was surprised by how puny the wire link was where the switch was supposed to go - it had to handle up to 4 amps at times. Most of the time the current required was between 1 and 1.5 Amps, well within the rating of a 2.5mm DC barrel connector I intended to standardise on.

First of all, after disassembling with a Torx screwdriver, and removing the battery pack, the original charging socket is removed to make way for the new power lead, and the wire link is removed form the empty switch position to allow make a beefier terminal to be put in for the positive of the new power lead.
After desoldering these, a bigger wire link is put in where the small wire link was, and the original charger plug opening is widened enough for the new power cable.

Then, cut the track to D8, the red LED that flashes whenever power is disconnected from the ATMega, and whenever the ATMega decides a charging session is in order. This is superfluous when an external power supply is used, and is an unnecessary annoyance. 

Having cut the track to D8, you can then prepare a negative terminal for the power cable. The positive terminal using a bigger wire link was a no-brainer, but there was no big fat nice place to solder the negative lead. Luckily, the back of the board is a ground plane, and a mounting screw in the middle of it was perfect for holding a negative terminal to the ground plane. Lacking a suitable tab, a second hand 13mm = 1/2inch copper pipe clamp was soft annealed in the fireplace, hammered flat, and trimmed to suit a patch of ground plane which had the solder mask scraped away.

After this, the power lead can be soldered to the +ve and -ve terminals.

And then put it together.

The unit can then have a DC barrel connector attached, paying careful attention that you make the positive lead (white stripe in the above picture) go to the centre of the DC barrel connector, which is the usual convention.

I will have the DC barrel connectors plug into a blank wall plate to the left, with DC barrel sockets. These barrel sockets will be wired to a compact 12V 3.3Ah SLA battery (only AUD$20 from Altronics!) which will be located further down the wall, in the wall cavity, with a standard wall plate covering the battery enclosure.

It is very important to have an inline fuseholder with a fuse, close to the battery, as shown above, to avoid exploding batteries and/or fused wires in the event of  accidental shorts. Lead acid batteries can explode too, if hydrogen leaks and finds a spark, but hey, other battery chemistries can explode too.

With the battery being terminated in a DC barrel connector on the wall plate, it can be charged with an SLA fixed voltage and current limited charger plugged in on an occasional basis, or, additional wiring can be run to the same wall plate to bring a charging circuit to the battery from a central location, which can be turned on as required, or fat DC cabling can be run to the controllers from a central location.

As a bonus, there's 12 volts on tap in the wall whenever you need it (within reason given the 3.3Ah capacity) for a radio transceiver perhaps...

As mentioned above, in a bushfire prone area, reliable roller shutters are important and mains power cannot be relied on in emergencies. Having a dedicated battery for each controller was an important consideration for us, and the mod described above even allows a separate power supply to be used with the controllers in case of emergency.

Cable, solder tag, and battery, about AUD$25. Even after adding a wallplate or two, some cable and a fuse and fuseholder, it sure beats a soon to be dead AUD$80 battery for each controller.

I'm sure the engineers were capable of making a more robust controller, but I can't help wondering if they had to contend with marketing who wanted a nice compact sleek unit, and went with 12x1.2Vx1500mAh AA NiMHs as a result.

I hope this helps similarly afflicted consumers out there, but it's not my fault if you void your warranty, kill your controller or hook up a high current power supply the wrong way around and melt something or burn the house down.


  1. Thats great ... I hope the company that makes those, sees this and feels like real idiots

  2. Thankyou!
    I have a few of these and replaced the batteries myself but was disappointed when after a few months the batteries failed.
    Instead of hooking up the batteries, do you think I can connect these to an appropriate voltage source powered by mains? The devices in question are old laptop chargers.

  3. @ Stefcio

    I found after experimentation that the controller with this mod will accept from about 12V DC to about 19V DC (but definitely not more than 19V - it refuses to work), when playing with the benchtop lab power supply.

    Initial surge currents were typically up to about 3 Amps, but one of the motors, strangely enough, on a smaller shutter, needed about 4 Amps briefly to get moving.

    So, a mains powered power supply capable of providing 12V-19V DC loafing along at 1-2 or so Amps but able to supply up to 4 amps briefly should work fine.

    It would pay to put a beefy diode (better than 4 Amps rated) in for reverse polarity protection, if the wires could get accidentally reversed with your sundry power packs, or if the power pack will deliver a touch over 19V.

    The shutter controller will try to initiate shutter movement briefly, but if the power supply is unable to provide the current required, the shutter controller will think the shutter has reached the limit of its travel and stop supplying juice to the motor - so you'll figure out pretty quickly if your intended power pack is up to the task.

    Incidentally, Wife Acceptance Factor (WAF) was increased by purchasing some white sheathed twinflex cabling....

  4. Anyone contemplating this mod should also check my earlier page with the initial teardown and analysis for additional background info.


  5. Most interesting: I have ten OzRoll shutters and have replaced about three batteries, with another four dying now. I have been contemplating dispensing with the in-unit batteries and connecting all (as they die) to a 12v golf buggy battery in my garage.

    Thanks for the info on the current: I wanted to put a fuse in series but didn't know what current to allow for. Obviously 40A (assuming all ten shutters were started at the same time) would be a bit OTT! Possibly a 5A fuse might do? What do you think?

    1. Only the initial surge current is going to be about 4 amps per shutter, after that it tapers off to 1.5 to 2.5 amps or thereabouts until the shutter is closed. A bit less for lowering, a bit more for lifting.

      I'd be surprised if you get them all moving at exactly the same time such that they draw more than 20 or 25 Amps in total.

      Maybe put a 30 amp fuse at the main battery itself, and then perhaps also 7.5 Amp fuses for each of the branches to each controller.

      I used 7.5Amp fuses for each individual controller, based on the fact that surge currents were typically not much more than 4.5Amps.

      I seem to be able to go for weeks on ~ 4 AHr SLAs before needing to recharge.

      Don't go crazy on the gauge of the power feed wires going to the controllers. If all the wiring between the controller and battery is too fat, and the battery is too big, there won't be enough voltage drop as current increases as the shutter hits its limits for the controller to know it has to stop. This is why I ended up using fairly fine alarm cable for the cable going into the controller.

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  7. I've had a bit of a study of the battery charging on these and it may not be as brain dead as you thought. It only charges the batteries hard if you have disconnected the battery - probably because it loses the charge counting - but this only happens once in the life of the product - or if the batteries are dead flat - in which case they need a full charge anyway. So I think the overheating you saw probably because the battery was disconnected at some time. Then there is actually an NTC on the PCB - just looks like a black SMT resistor and it tripped out if it got really hot - but the batteries need to be against the PCB for this to work - which it is when it is packaged up. The rest of the time it replaces what was used plus a little more - it seems to know it's steady current draw and calculates the charge used in the current sense when operating a motor - then it replaces this in 160mA spurts. So everything I observed gels with your observations if you had the cells out when assessing it and had disconnected the cells at any time - just this not normal operation in real life.
    Sux about the actual battery life obtained though given how much trouble they went to on the charge side.

  8. Is it possible to provide a bit more detail on how to remove the roller shutter axle?

  9. Can you please let me know how did you dismount the axle?

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