Jump Starting with car Battery?

jconway607 · Nov 10, 2019

My 96 R1100RT seems to always have a battery leak down problem. A few days off the charger and it barely cranks. A few weeks ago it get really low and it would hardly start, but did. Then, of course, the ABS lights showed a default. Normally after riding a few miles I can cancel them by restarting, but not this time. I had the Odyssey 680 battery supposedly load tested and it passed. 12.8 or so volts. It's about three years old. Took the starter off and had it tested, and it met the specs. Just put it back together and tried it, and again, pretty slow cranking, and the ABS lights flashing. I'm beginning to wonder if the battery is the problem after all. I thought I might try jumping it with my car battery to see if it cranks better, and if it then doesn't have an ABS problem, before I go buy another battery. If I do get another battery it will be back to a regular lead acid, which I believe GSaddict says is better for these models. Any thoughts on if I will burn up the electrical system on the bike with the larger car battery?

pglaves · Nov 10, 2019

Provided you connect the cables correctly and are using a 12 volt battery jump starting with a car battery will not harm the bike. The amount of current that will flow will depend on the draw of the bike's components and not on the capacity of the battery.

Omega Man · Nov 10, 2019

I have jumped a bike with a car- no problem.

https://forums.bmwmoa.org/showthread.php?52968-My-battery-died-yesterday

I have found when a battery is left in the system, it’s difficult to get to the root of the problem. A way to get closer to the problem, with the battery in-line, is to measure the available voltage while cranking the engine.
If there is a severe draw-down, the battery is suspect.
If the battery was removed from the system and run off the car......and ran fine, it would be another way to test the starting.
OM

RadioFlyer · Nov 10, 2019

As Paul says the bike will pull the amount of current it needs from the car battery and not more BUT you should not boost from a car battery in a running vehicle. This is because the regulator in the bike (a crude shunt type in many cases) may attempt to regulate down the boosting vehicle's charging voltage. A shunt regulator will handle the full current output of the bike's alternator but not necessarily that of the boosting vehicle.

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flhfxd · Nov 11, 2019

No problem to boost from a car but MAKE SURE the car isn't running.

Omega Man · Nov 11, 2019

Never had trouble jumping with running or not running :dunno

I would try to avoid the start cycle of the donor vehicle during the attempted jump. Once the donor vehicle is running, unless there is some problem with the donor vehicle, it’s stable.
I have found that a “jump” is no problem with a stable power source.
OM

gsaddict · Nov 12, 2019

RadioFlyer said:
As Paul says the bike will pull the amount of current it needs from the car battery and not more BUT you should not boost from a car battery in a running vehicle. This is because the regulator in the bike (a crude shunt type in many cases) may attempt to regulate down the boosting vehicle's charging voltage. A shunt regulator will handle the full current output of the bike's alternator but not necessarily that of the boosting vehicle.

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Oilheads & Hexheads do not have shunt type regulators. You can safely jump with an external source.

Waterheads on the other hand, do. It would not be wise to jump from a running vehicle, especially if revving high.

k1200lt00 · Nov 12, 2019

I will make sure the car is no running other wise you have a good chance of burning out the ECM. I seen it happen more the once. You are better of giving the battery a full charge as with a low battery you are putting more strain on the electrial system.

RadioFlyer · Nov 12, 2019

GSAddict said:
Oilheads & Hexheads do not have shunt type regulators. You can safely jump with an external source.

Waterheads on the other hand, do. It would not be wise to jump from a running vehicle, especially if revving high.

The F bikes also have shunt regulators. I don't know about the S or K bikes.

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gsaddict · Nov 12, 2019

RadioFlyer said:
The F bikes also have shunt regulators. I don't know about the S or K bikes.

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I was responding to a boxer thread.

RadioFlyer · Nov 13, 2019

GSAddict said:
I was responding to a boxer thread.

I was just trying to demonstrate thar the earlier boxers are the exception. Shunt type regulators are very common on bikes.

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pglaves · Nov 13, 2019

RadioFlyer said:
I was just trying to demonstrate thar the earlier boxers are the exception. Shunt type regulators are very common on bikes.

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Of course, because they're cheaper.

jconway607 · Nov 13, 2019

I'm still assembling the wires needed to jump start the bike from a car battery. But before I did that I wanted to check the voltage draw from the Odyssey battery alone. This is it:

1) Battery voltage reading after being on charger= 13.3 v
2) With the key switch turned on (headlights, dash lights) =11.8 v
3) Cranking the engine= 8.2 v
4) With engine started and running= 14.1 v

Admittedly, this is when the temperature is a 22 degrees. But as I stated before, this was causing problems at somewhat higher temperatures also. I would guess that 8.2 volts is well below what it takes to trigger the abs fault light. Anyone know what that threshold is? So, a) even though the starter read an 80 amp, and roughly10 volt draw off the bike, on it it seems to be pulling a lot more, so maybe it is actually broken. Or, b) like my 1972 Ferguson backhoe with no glow plugs, these bikes shouldn't be started and run below about 50 degrees. Any thoughts?

Omega Man · Nov 13, 2019

I would say it’s time for a new battery.
OM

gsaddict · Nov 13, 2019

jconway607 said:
I'm still assembling the wires needed to jump start the bike from a car battery. But before I did that I wanted to check the voltage draw from the Odyssey battery alone. This is it:

1) Battery voltage reading after being on charger= 13.3 v
2) With the key switch turned on (headlights, dash lights) =11.8 v
3) Cranking the engine= 8.2 v
4) With engine started and running= 14.1 v

Admittedly, this is when the temperature is a 22 degrees. But as I stated before, this was causing problems at somewhat higher temperatures also. I would guess that 8.2 volts is well below what it takes to trigger the abs fault light. Anyone know what that threshold is? So, a) even though the starter read an 80 amp, and roughly10 volt draw off the bike, on it it seems to be pulling a lot more, so maybe it is actually broken. Or, b) like my 1972 Ferguson backhoe with no glow plugs, these bikes shouldn't be started and run below about 50 degrees. Any thoughts?

A properly charged Odyssey in good condition will crank at over 11v.
The motronic does function correctly at 8.2v

jconway607 · Nov 14, 2019

GSAddict said:
A properly charged Odyssey in good condition will crank at over 11v.
The motronic does function correctly at 8.2v

Thanks GS. Good to know the volts can go that low and the abs not default. I think I will wait until it gets into the higher 30s to try the battery jump part of this test. I didn't mention it earlier, but after the bike is run for a few miles, it starts instantly. No slow cranking.

Even before I had this current problem, I noticed that as the temperature dropped, say 60 to 50 degrees, the bike had to be kept on the charger sooner. Are BMW twins just generally difficult to start in colder weather? Two large cylinders and pretty small batteries?

gsaddict · Nov 14, 2019

jconway607 said:
Thanks GS. Good to know the volts can go that low and the abs not default. I think I will wait until it gets into the higher 30s to try the battery jump part of this test. I didn't mention it earlier, but after the bike is run for a few miles, it starts instantly. No slow cranking.

Even before I had this current problem, I noticed that as the temperature dropped, say 60 to 50 degrees, the bike had to be kept on the charger sooner. Are BMW twins just generally difficult to start in colder weather? Two large cylinders and pretty small batteries?

In the 40's and lower, Oilheads don't like starting. The 20w50 oil is too thick.
Switching to a lighter oil like 10w40 will help with winter riding,

jconway607 · Nov 14, 2019

GSAddict said:
In the 40's and lower, Oilheads don't like starting. The 20w50 oil is too thick.
Switching to a lighter oil like 10w40 will help with winter riding,

Again, good to know. And also what I suspected. The 10w40 oil would probably definitely help. I guess I can't blame the bike. Thick oil is hard to move when cold. I'm going to make a note to myself: 45 degrees or so is the cut off for starting it. I usually never try to start it during cold weather anyway, but the thought of having to wait till spring to diagnose/ fix the abs problem is irritating. Well, that's life.
I wonder if the K bikes and vertical twins don't have this weather problem? Seems like my Pacific Coast V 45 did not.

BC1100S · Nov 14, 2019

jconway607 said:
Again, good to know. And also what I suspected. The 10w40 oil would probably definitely help. I guess I can't blame the bike. Thick oil is hard to move when cold. I'm going to make a note to myself: 45 degrees or so is the cut off for starting it. I usually never try to start it during cold weather anyway, but the thought of having to wait till spring to diagnose/ fix the abs problem is irritating. Well, that's life.
I wonder if the K bikes and vertical twins don't have this weather problem? Seems like my Pacific Coast V 45 did not.

K bikes have more cylinders and are therefore working to compress fewer cc's per revolution. i.e. 1200cc 4-cylinder = 300cc per cylinder versus 1200cc 2-cylinder = 600cc per cylinder.

Anecdotally, I've had to start my R bike in 30F while running 20W-50 and, while it turned over more slowly, it did start right up. I'l hazard a guess that the slower turnover was a result of a chilly battery. I'd think that it would have to be dang cold for the viscosity of the oil to make a difference when starting the bike. About a hundred years ago I was in -15F weather with a British sports car that had 20W-50 oil in it. It started.

gsaddict · Nov 14, 2019

jconway607 said:
Again, good to know. And also what I suspected. The 10w40 oil would probably definitely help. I guess I can't blame the bike. Thick oil is hard to move when cold. I'm going to make a note to myself: 45 degrees or so is the cut off for starting it. I usually never try to start it during cold weather anyway, but the thought of having to wait till spring to diagnose/ fix the abs problem is irritating. Well, that's life.
I wonder if the K bikes and vertical twins don't have this weather problem? Seems like my Pacific Coast V 45 did not.

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