Running a MoDic 3 Without Batteries?

[E36Ron]

Does anyone know a way of operating the original MoDiC 3 with the Orange Head on mains power, independent of the state of the two NiMH batteries?

The battery system on this device is insane.

It never seems to have occurred to the designers, Kontron Elektronik, that anybody would want to just IGNORE the batteries and simply run it off AC power (or maybe that's the way BMW, being BMW, designed it).

Here's the (various) problems:

1. If you run the MoDiC plugged in on its charger base, the SCO Unix files that undergird DIS on this device TEST THE BATTERIES before allowing DIS to load. If they find the batteries are either depleted, or require a "maintenance service" (designed to "refresh" the batteries by cycling them endlessly overnight -- or maybe even over several days -- to "prolong their life"), they will not let the program load.

A way around this is to ensure that both the internal battery and the main battery are fully charged, then take the MoDiC OFF the charging station so it HAS to load from the batteries, and then it will load, irrespective of "maintenance cycle" status (maybe after one or two tries).


2. Fine. Then you think, OK, having bypassed that test, I'll put it back on the charging station so that the internal battery charges continuously (that's the only way you charge the internal battery), and presumably power also goes to the MoDiC itself, and get on my merry way, running diagnostics, etc on my 1990s era cars.

But no. After about an hour, it alerts you that the main battery is depleted, and needs to be urgently replaced with a fully charged one. But I'm PLUGGED IN, for Pete's sake! Can't you leave me alone? As it is, I have to wait forever for you to do your thing at 9600 baud. I don't want to have to think about batteries!


3. OK, another workaround. The MoDiC kit includes a DC-to-DC power pack. You plug this into the car's cigarette lighter, and the instructions say "MoDiC and charger are fully operational." (This was designed to allow you to drive the car [with an assistant] using the MoDiC's [non-functional] wireless connection to the orange head under the hood, and observe stuff while the car is operating on the road. Great idea, but if it lets me operate the MoDiC all day without worrying about the batteries, I'll take it.)


4. But no. (Does this begin to sound familiar?) With the DC-to-DC power pack connected, the MoDiC runs fine, even with the main battery unplugged. So far, so good. But now it starts to alert me -- every two minutes -- that it is about to shut down due to "overheating of the backup battery." I keep dismissing this dialog (by clicking OK, which is all you can do), and the device keeps right on operating. It's a hot day, I must be right on the edge of overheating, but not past it.

I find I can get rid of this dialog by unplugging the DC-to-DC power pack, so the backup battery is not being continuously charged. But then I'm back to using the device on its batteries. This will be OK for maybe 45 minutes if I periodically check the battery status, and plug back in the DC-to-DC pack in sufficient time.

Oh, and by the way, if you thought that because I can unplug the main battery while using the DC-to-DC pack, I could also just unplug the backup battery, or let it go flat, you'd be WRONG. As soon as the backup battery reports dead, the whole unit shuts down.


So there you have it. The entire system depends ultimately on the availability and condition of the backup battery.

Who in their right mind would design a system like this?

Well, irrespective, I'm looking for a more elegant way around it. Any ideas?

Regards,

-- E36Ron


1996 328Ci/A
1990 850i
1997 850Ci

[David Mc]

Why not just replace the original NiMh batteries? There is obviously a problem with them - evident from the fact that you get the battery overheating warning when on DC power - indicating that the thermistor is detecting abnormally high resistance in the internal cells. Alternatively, take the unit to an electronics repair store and tell them that you want it modified to run on DC power, they will remove the internal cells and if necessary, modify the DC power jack accordingly.

[E36Ron]

Hi David:

This is a 1999 Pentium computer running SCO Unix scripts to load the DIS BMW diagnostic graphical touch-interface interactive software. The internal circuitry details are not generally available. The problem is in the software, so, without modifying the software, I would think any hardware change would have to mimic the expected behavior of the batteries at full charge in order not to trigger software action to shut down, etc.

I think I have a better chance finding readers of this forum who have actually tinkered with this software, than I would have of finding an electronics repair store that could successfully take this on at the purely hardware level.

I actually don't mind that it runs on batteries. All I want is that it also run without protest on mains-derived DC power, just like any laptop has always been able to do.

PS: the batteries were new 5 years ago, and have only been cycled perhaps a 15-20 times for the various times the MoDiC has been used. Does the kind of internal resistance you believe is taking place here depend upon number of cycles of use, or elapsed time? And if cycles, shouldn't it take a lot more than 20 before failure?

Can the internal resistance be reduced by "conditioning," as the MoDiC is designed to do? Or once it builds up, it's done?

The problem is only with the internal backup battery (readily accessible for replacement, at about $90 a pop). It seems I've had to condition it overnight or for several days every time I use it, even if it's fully charged. All this battery management is a real burden, unnecessary in my opinion even before the days of lithium-ion batteries, if there was just a simple way to plug it in and use it on mains power.

Regards,

-- Ron

[David Mc]

Ron, from the symptoms you describe the replacement batteries sound like the root of the problem. The problem with tinkering with the voltage settings in the software is that the current settings have been established to prevent failure of the program, so altering them may wind up with a catastrophic software failure. You are correct in your assumption that any hardware modification would need to present a voltage consistent with fully charged internal batteries (so it would need to be a fully regulated source). From the sound of it, the DC to DC adapter is designed to continuously top up the internal battery charge, thereby using the batteries as a means of regulating the power supply, rather than acting as an independent power source. Once the internal batteries develop high resistance (due to age or deterioration), they generate heat and attempt to draw additional charging current, which is the reason that the software failsafe becomes active. A hardware mod would in my opinion be far safer than a software mod and should not require any advanced electronic knowledge of other internal circuitry not related to the power supply. From experience there are lots of vendors selling "replacement " batteries that are of vastly inferior quality so it is very easy to be stuck with dodgy batteries, even for experienced techs.