If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

1978 100/7 reverse ground

Post Reply
User avatar
75R60
Posts: 32
Joined: Mon Jul 25, 2016 11:24 pm
Location: Boston

1978 100/7 reverse ground

Post by 75R60 »

IMG_2284.jpeg
IMG_2284.jpeg (20.88 KiB) Viewed 3570 times
I'm working on a 1978 R100/7. The bike has run great no problems, I'm just going through it making sure it's ready for a cross-country ride. I replaced the battery with a lithium ion PO4, things are looking good with the bike so I decide to hook the battery up real quick just to make sure all the electrics look good as I had the headlight out in order to paint it.

Here's where it all went wrong. The terminals on the lithium battery are opposite visually where they are on most batteries. There's a picture here with the old battery in the background you can see they're reversed. Anyway I just touched the ground to the negative terminal on the battery and I hear this click click pop and smoke comes from the black plastic hood above the starter. Yup I did that. I feel like such an idiot! I'm keeping the language clean here but if there was wallpaper in my garage it would be on the floor now.

Well I pulled off the front cover which is a bear because it's got a oil cooler which has to be removed in order to remove the cover. I removed the diode board and it smells like geraniums as you can imagine....

I'm assuming for starters I need to replace this thing, interestingly two of the rubber supports were broken and I'm about to take this on dirt roads cross the country so maybe it's a good thing I discovered that? I know I'm really searching for a silver lining here but my plan is just to source out this diode board and replace it. I don't think I want to get into going for the super electronics. I've had these bikes a while and I like the old diode boards fine. What are you guys think about replacing just the diode's? Also any thoughts on whether I might have smoked something else?
Attachments
IMG_2283.jpeg
IMG_2283.jpeg (48.16 KiB) Viewed 3570 times
Dang
‘75 R60/6
‘75 R90/6
#therippleride

User avatar
schrader7032
Posts: 9016
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: 1978 100/7 reverse ground

Post by schrader7032 »

My thought would be to put it back together and see what happens with charging. The diode board wouldn't affect the ability to start the bike...you could then monitor the voltage to the battery.

Or you could test the diode board:

https://robfrankham.com/diode-board-test

Beyond that, I'd end up sourcing a replacement with Motorrad Elektrik or try getting a Thunderchild board. I've read about some satisfied customers with the Thunderchield. But Rick at Motorrad Elektrick is a good guy to support.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

User avatar
75R60
Posts: 32
Joined: Mon Jul 25, 2016 11:24 pm
Location: Boston

Re: 1978 100/7 reverse ground

Post by 75R60 »

Good idea thanks Kurt. So I stuck it back in, hook up the battery and the red charging light comes on and stays on. However the lights work and the starter turns over. I found a new $70 diode board on eBay listed by EME. I like those guys too. Don’t know them but I’ve bought a bunch of stuff off of them. Never a hitch.

I used your link to test this diode board and half of them are blown or I should say two of the three terminals for the alternator hook up do not pass power. I’ll get back to it on the weekend
Dang
‘75 R60/6
‘75 R90/6
#therippleride

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: 1978 100/7 reverse ground

Post by srankin »

I have purchased parts from EME as well as Motorrad Electrik, they are great people.

One thing about the aftermarket diode boards is they are much better than the original BMW units, at leas visually they are better built and look more robust.

You mentioned something about the rubber mounts being broken, a common problem with BMW. The recommendation is to replace them with the solid metal mounts. EME sells them. Sorry, I don't have a long explanation as to why it is suggested to go with the solid mounts other than for added grounding and perhaps heat dissipation. I am sure Snowbum in one of his articles gave a good case for it as well as other BMW experts.

Have fun, St.
Owner of a 84, R80RT and 78, R100RS

User avatar
75R60
Posts: 32
Joined: Mon Jul 25, 2016 11:24 pm
Location: Boston

Re: 1978 100/7 reverse ground

Post by 75R60 »

I’m familiar with the warning given by Snowbum. I usually try to reference his guidance before dropping an obvious question on y’all. That said, he provides so much information in his knowledge base, that sometimes I prefer to delve around the peripheral :-). So thank you guys!

I will definitely be replacing those rubber mounting posts with the solid ones, my next question is this. I will be using this bike in somewhat of a adventure mode, I’m doing the the TransAmerican trail in June. This bike will Daly be charging batteries cameras etc. and I’m wondering about the possibility of going with the $300Replacement that EME sells for the extra wattage. I see I have mistaken them for the other suggestion that Schrader made. I’ll have to check that suggestion out as well. At the very least I will be replacing it with the thunderchild as he suggested as it’s not much more money and seemingly a far better option. Any insight on whether you think the EME replacement will meet my charging need? I would be replacing the regulator as well.
Dang
‘75 R60/6
‘75 R90/6
#therippleride

User avatar
schrader7032
Posts: 9016
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: 1978 100/7 reverse ground

Post by schrader7032 »

There is a settable voltage regulator...possibly higher outputs from the usual places. An adjustable regulator could be good for someone making around-town trips, not getting out on the open road for steady RPMs for longer durations. This could be something to consider for your adventure. But it should be adjusted back if you are no longer in that mode as it might over charge the battery.

IMO the R100/7 is not the bike I'd be taking on a trip like that! :shock:
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: 1978 100/7 reverse ground

Post by srankin »

Uh, I may be a trifle confused. I understand the need to change the diode board due to the short out. The only advantage the EME board has over the BMW ones is it is more robust. The diode board changes AC current to DC, it does not have anything to do with voltage or amps.

Now, if you are talking about a different voltage regulator, that is a different animal. and Kurt is right, there are adjustable ones out there.

Just cranking the voltage up by adjusting the voltage regulator only works if the alternator is putting out enough watts or has high enough amperage. You can crank up the voltage on a regulator to its highest setting but if the load on the system is such the drain on the alternator can't keep up, the voltage overall will drop. Does this make sense?

So for example on my RT, I had the stock charging system. With just the normal lights, ignition and factory heated handgrips, the voltage would be at 14 volts. When I added a heated jacket and pants, the voltage dropped because the stock alternator could not keep up with the load added to the system. Installing a 600 Watt alternator increased the output and as such now with all my electrical stuff going, I am charging at the required 14 Volts.

So, it is amps and watts at play to get the voltage, forgive me, I haven't done electronics or electrical theory in a long time so I may not make a lot of sense.

To be honest, your stock charging system should work just fine for charging cameras, phones and the normal loads of lights and such on your bike. Phones and cameras have a very low amperage draw. I would be concerned more if you were going to be wearing full electric clothing, heated grips and a bank of driving or fog lights. The stock system would likely not keep up with all that.

I sure hope I made some kind of sense, I am sure someone will point out my errors and I appreciate it.
Oh I agree with Snowbum's articles, I like the guy but sometimes I get cross eyed reading his stuff. I am lazy so I let Kurt the moderator do all of that stuff, he is good at it.
Cheers. St
Owner of a 84, R80RT and 78, R100RS

User avatar
75R60
Posts: 32
Joined: Mon Jul 25, 2016 11:24 pm
Location: Boston

Re: 1978 100/7 reverse ground

Post by 75R60 »

Thank you for your input! I understand your evaluation of my charging system. I think it’s back to the Thunderchild for me. I’ll use the eBay diode I bought as a back up. Good to know the stock system will keep up with the trickle charge of keeping the electronics happy while I’m driving

I’m excited about bringing this bike cross country. I know it’s not ideal but it will be fun!!
Dang
‘75 R60/6
‘75 R90/6
#therippleride

User avatar
75R60
Posts: 32
Joined: Mon Jul 25, 2016 11:24 pm
Location: Boston

Re: 1978 100/7 reverse ground

Post by 75R60 »

Well I’ve moved on to other things so I thought it would be nice to post a follow up.
I ended up buying the 400 watt charging system with rotor, diode board with standoffs
4BC25266-A34B-4760-BBC9-92778D32B338.jpeg
, rectifier and stator from EME. It was a pretty straightforward install, and on completion the bike started up and charged as expected.
No damage to anything else electrical related as far as I’ve discovered.
Since then I’ve rebuilt the master cylinder and front caliper. The bike leaves on Sunday to do the TAT for the next month.
Thanks again for your insight!

Follow us on Instagram @therippleride
Dang
‘75 R60/6
‘75 R90/6
#therippleride

User avatar
srankin
Posts: 1054
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA
Been thanked: 14 times

Re: 1978 100/7 reverse ground

Post by srankin »

Hey, good news! I think you will be happy with the extra oomph of the new charging system. While the stock system was adequate for most people, it never hurts to upgrade. The kit you installed is as you say easy to install.

One of the great things now a day is some of the upgrades people have designed and marketed to correct BMW's short comings. Upgrades that are easy to install and work well plus, don't cost a fortune.

Enjoy the riding, St.
Owner of a 84, R80RT and 78, R100RS

Post Reply