Using a battery charger with the cables still connected on '98 E320 - PeachParts Mercedes-Benz Forum

knuckle_buster · #1 03-28-2007, 03:24 PM

Everyone knows (except my brother, apparently) that many MB manuals say to disconnect the battery before using a charger, because damage to electronic components can occur. Does anyone know which components are likely to be damaged on a 1998 E320 4matic? Has anyone actually witnessed such an occurrence?

david s poole · #2 03-28-2007, 03:50 PM

what they are worried about is that commercial chargers can throw as much as 17volts at a battery which can be a problem with the computers that have keep alive power to them when key off.

loubapache · #3 03-28-2007, 03:52 PM

I doubt someone has witnessed one with a good charger.

I use a battery tender type of charger in the winter for all my cars (the newest is 2003). I do it every a couple of weeks to those that are not driven regularily.

This type uses a small current to charge the battery and once the battery is charged, it'll stop charging or uses a even smaller current to maintain the charge.

knuckle_buster · #4 03-28-2007, 04:27 PM

I'm afraid this isn't what I'd call a "state-of-the-art" charger. It has no integrated circuits, only a transformer and a couple of diodes.

I hadn't driven the car in a couple of months because I needed to do some work on the EGR system. When I completed the work, the battery was low, so my brother connected the charger where he had seen me connect jumper cables previously. It was only connected for 10 minutes or so before I saw it.

Everything seemed fine when I first drove it. Then I noticed the A/C wasn't cooling. I did some investigation and noticed that the compressor runs when the car is first started, but after 5 minutes it stops and does not restart. It has plenty of freon. I first suspected one of the temperature sensors: coolant, evaporator, or ambient. But I've initially ruled those out, since turning the car off then restarting makes it work again (for 5 minutes), even if the car is hot. I still need to remove the control unit so that I can verify those resistance values.

I decided to drive it across town, and while doing so, I turned the system off and back on. Then the blower quit working. Once again, turning the car off and restarting made it work again.

My manual says that when replacing the AC control module, "version coding must be carried out," but it doesn't tell me how to do that or even what it means. Maybe I erased it's memory and it needs to be recoded?

Also, does anyone know if the keys needed to remove this unit are the same as the ones used to remove the radio?

Thanks much.

G-Benz · #5 03-28-2007, 04:32 PM

I think the real concern is the "impulse charge" feature contained in most battery chargers...you know, the ability to "jump start" a car by hitting that switch that makes your cockpit courtesy lights illuminate like stadium mercury floods!

mpolli · #6 03-28-2007, 04:39 PM

They are using the old "better safe than sorry". I think the chances of damage are generally low. There would have to be some unusual circumstance to cause damage. Electronic modules in 12V based cars are usually built to withstand 16V continuously (24 hours) and "load dump" transients up to 80V briefly and they can usually withstand reverse voltage briefly. One problem could be hooking up a charger to a battery with loose connections, so that the battery does not load down the charger and the voltage floats up to some high voltage. So then the car is seeing the high voltage but the battery is not. I would say just hook up the charger and put a voltmeter on the clamps and make sure the voltage is below 16V. If it is then you should have no problem.

Mike

TMAllison · #7 03-28-2007, 04:53 PM

Read Steve B's article concerning climate control display before pointing finger at brother....may not be his doing.

http://www.continentalimports.com/ser_ic40142.html

Strife · #8 03-28-2007, 08:43 PM

Inexpensive chargers have really bad ripple, and this may actually be GOOD for a battery but bad for electronics. It's true that most car electronics are designed to survive somewhere over 16 volts but it doesn't do them a world of good. It can exponentially shorten the life of a lamp. It also may trip the OVP and blow a fuse.

The battery acts like a capacitor to smooth out the ripple, except when it's completely dead and shot, like an internal break or a dead cell. Then, the ripple goes through the rest of the car if the battery is not disconnected.

Matt L · #9 03-28-2007, 08:50 PM

The 210 lacks the OVP, so this isn't an issue. I'm not sure if there's much of a chance for damage with a typical consumer 10A charger, but I tend to disconnect my battery before hooking it up. There are electronic parts all over this car.

The last time I charged it, I disconnected the negative lead from the body and connected a jumper cable from the underhood positive connector to the positive lead of the charger, so I could hook up the charger without removing the rear seat.

And, at the risk of becoming a broken record about this, I had to set the clock and enter the radio code but nothing else lost its synchronization.

knuckle_buster · #10 03-28-2007, 10:38 PM

Thanks Terry (and Steve B.). That's the coolest thing I've seen in a long time. I'm going to check it out right now. My father-in-law has a 1995 350 Turbo Diesel (not sure what the chasis number is on that one), and he has replaced TWO evaporators. So I was very nervous about that. I'll be keeping my fingers crossed.

Regardless, I'll be going easy on my brother, since he's 5 inches taller and 100 pounds heavier.

Quote:

Originally Posted by TMAllison

Read Steve B's article concerning climate control display before pointing finger at brother....may not be his doing.

http://www.continentalimports.com/ser_ic40142.html

knuckle_buster · #11 03-28-2007, 11:17 PM

Good grief... I didn't take enough paper to write down all those error codes: in-car temp sensor error, ECT sensor error, freon pressure sensor error, sun sensor error, series interface connection to instrument cluster error.

The actual values are a little confusing. It appears they are a mixture of C and F. The chart on the link page says that refrigerant temp is in F, and the text on that page says that evaporator temp is in C. I'll know more when I do the test again while driving tomorrow.

It appears that pressing both Auto buttons at the same time clears the error codes.

If all those codes come back, it would seem to be the controller.

Matt L · #12 03-28-2007, 11:21 PM

My '96 is all in C. Some are all in F. I don't know if any are mixed, but it wouldn't surprise me very much.

knuckle_buster · #13 03-29-2007, 09:07 AM

Yes... I now think they are all in C. The two that were high were engine coolant and evaporator temp. After driving it this morning, it makes sense that the ECT was 57, which appeared to be F. But 57 C is reasonable for engine coolant a few hours after driving.

It's the evaporator temp sensor that now seems to be the culprit. It's reading 66 (~150 C), which seemed like degrees F.

Fortunately none of the error codes came back.

On a side note, what a cool system (no pun intended). Who would have thought that your air conditioner could tell you your vehicle speed or battery voltage?

david s poole · #14 03-29-2007, 09:33 AM

the evap temp sensor in that car is well known for failing and produces exactly the symptoms you describe.