Intermittent dead short while starting

This is more a question than a suggestions or fix. I know just about enough to get into trouble re newer battery tech. Here is the question, can the newer battery and its internal protection circuit cut off not only on level of output but also on level of input? I would think, do not know, if one removed the input to the battery from the reg/rec and see which way the issue is coming from? Or is this not a good idea?

i'm at work so i can't rabbit hole this too much but this webpage has some info.

www.ltw-bms.com/news/news352.html

I would never, or would I, ask or expect anyone to go a rabbit hole. So on that point go back to work. Just indicating my lack  regarding the newer battery tech. Thank you for the link, it did indicate it works both ways. Something I did not know, or at least do not remember from what I have read.

You guys are great. Tons and tons of good info and things to check out. I haven’t had a lot of time to work on the thing working afternoons and trying to spend all morning with the kids. 

I believe my next steps are going to be calling the starter and alternator repair shop to have my starter motor checked out and trying to find an AGM battery that fits the space I have available. I’d like to also do the ground and resistance test as well. 

I’ve come to this place many times when looking for answers or help and you guys always have a wealth of knowledge. I appreciate that a lot.

Well, went and bought an AGM battery this morning after testing the starter for positive line resistance and it going down to 0V after a second of cranking. Installed the new battery and it fired right up. Put the original reg/rec back on and idled it for a few minutes 4 or 5 times. Didn’t have any issues. 

Not saying I’m in the clear, but the BMS system was certainly not helping my issues. 

84_GPz750 wrote:

Well, went and bought an AGM battery this morning after testing the starter for positive line resistance and it going down to 0V after a second of cranking. Installed the new battery and it fired right up. Put the original reg/rec back on and idled it for a few minutes 4 or 5 times. Didn’t have any issues. 

Not saying I’m in the clear, but the BMS system was certainly not helping my issues. 

Just out of interest what did the voltage "drop down from ?" - I would expect it to be no more than 0.5v from the get-go and cranking should have no effect !!!

With one lead on the positive battery terminal and the other on the positive lug of the starter I showed 13.2V, full battery voltage. I attributed that to the fact that with the starter solenoid “open”, that lug on the starter is essentially ground. Am I way off? 

84_GPz750 wrote:

With one lead on the positive battery terminal and the other on the positive lug of the starter I showed 13.2V, full battery voltage. I attributed that to the fact that with the starter solenoid “open”, that lug on the starter is essentially ground. Am I way off? 

No you are correct, thanks for clarifying

Well, back again. Was measuring voltage across the battery terminals while cranking the bike over. After it started up, the voltage kept climbing and I shut it down when I looked over and saw 18V. This is after I swapped the stock reg/rec back on. Only running around 30 seconds.

This morning, I checked over the ground wire from the reg/rec harness and found no issues. I de-pinned the brown/white voltage sense wire going into the reg/rec but didn’t have a replacement male spade to fit the plug. Without the sense wire, it also climbed to over 15V.

I swapped the LiPo compatible reg/rec back on that I had on it with the lithium batteries and it charged to 13.4V and never went higher at idle.

My guesses are bad original reg/rec or not dumping excessive voltage to ground like it should. I’d have to lean toward the bad part since the other reg/rec is not overcharging the battery but didn’t want to throw more money away without having a second opinion. Thanks

Yeah, it sounds like your old regulator was having issues.
I would think the new reg/rec should be fine with the agm battery.
You may get a small battery voltage display for your dash to see if the reg rec is charging properly when you are riding.
Battery tender makes a small display that may work.

Yes
Disconnected brown sense wire will do that

Thanks @JR I figured as much. I only had it disconnected during one of my tests. Bought a used stock reg/rec for $24 that'll be here this weekend.