How to spot a weak battery?

[Don Sparlin]

Just purchased a used 5 year old x2, golf version. Suspecious of weak batteries.

Having charged for over 12 hours, I rode down the hill and back up again. Slow going up, but made it. On the charger, then down the hill (slowing due to full charge) and off for 2 miles of flat nature trail (side walk) Back up the same hill as on the previous day: Slow, slower, then "soft" (no stabilizing feedback) and dumped in the gutter of the street. At 77 yrs, it take a while (5 minutes) to get upright. The InfoKey showed full charge, but the loss of stabilization says weak battery. Next step is to fully discharge and recharge since I don't feel that the battery info column is showing me anything useful: It has never gone down even one bar!

Riding in my cow pasture yard with lots of clumps and divots, I went slowly due to the roughness, then got one wheel stuck in a depression, big spin and down again. My golf course is a cow pasture with nice greens: I hear that some golf courses have smooth grass!

Looking for any suggestions for battery check for high internal resistance: You would have the 75 volt terminal voltage with low load, but be unable to deliver large current on demand.

Don Sparlin
Experimental Physics Professor Emeritus

[Bob.Kerns]

Originally Posted by Don Sparlin

Just purchased a used 5 year old x2, golf version. Suspecious of weak batteries.

Having charged for over 12 hours, I rode down the hill and back up again. Slow going up, but made it. On the charger, then down the hill (slowing due to full charge) and off for 2 miles of flat nature trail (side walk) Back up the same hill as on the previous day: Slow, slower, then "soft" (no stabilizing feedback) and dumped in the gutter of the street. At 77 yrs, it take a while (5 minutes) to get upright. The InfoKey showed full charge, but the loss of stabilization says weak battery. Next step is to fully discharge and recharge since I don't feel that the battery info column is showing me anything useful: It has never gone down even one bar!

Riding in my cow pasture yard with lots of clumps and divots, I went slowly due to the roughness, then got one wheel stuck in a depression, big spin and down again. My golf course is a cow pasture with nice greens: I hear that some golf courses have smooth grass!

Looking for any suggestions for battery check for high internal resistance: You would have the 75 volt terminal voltage with low load, but be unable to deliver large current on demand.

Don Sparlin
Experimental Physics Professor Emeritus

The Segway monitors the condition of the battery. It's hard for us outsiders to judge the details, but certainly low voltage under load is one of the conditions that will trigger an alert, and eventually an emergency shutdown. But it will also refuse to start up when it detects that a battery is out of spec. Modern large batteries come with integrated Battery Management Systems that monitor state and control charging, so undetected cell failures are unlikely.

The safety features should avoid you being dumped due to the hypothesized cause, if you don't ignore them. Make certain you know about the stick shake warning, and have tried out the emergency shutdown sequence; details are in the manual (which is available online if you don't have a physical copy).

That still leaves unanswered, how do you tell if your battery has high internal resistance. Without access to a dummy load, I don't have a good answer. Reduced peak torque output -- that is, the Segway decides it needs to slow down sooner than otherwise, will give you a clue, but you have to be familiar with normal behavior to make the comparison, and it's still rather subjective.

MTOBATTERY can test your battery for you, but that will involve time and money.

If you can find someone to temporarily swap batteries with, you can tell if the problem is related to the battery. Combine that with difficulty climbing hills, and high internal resistance would be a logical inference.

I really wish the Segway exposed more operational data; it would help people like you or me better understand their operational characteristics, as well as diagnose problems. A graph of voltage as you climb your hill would tell you what was going on with the battery as a system. Detailed data from the BMS would be even better -- voltage across each cell...

[dgbint]

Originally Posted by Don Sparlin

Looking for any suggestions for battery ......

Hi Professor.

Easy solution.

1
Charge it up, say overnight.

2
Turn it on to get smiley face, lean it against a wall ( inside and safe where nobody can touch it ) and leave it running with nobody aboard.

3
The battery bars will go down with time, until it is flat and turns off.
If time is less than 12 hours, your batteries are weak.
If time is in the range 12-24 hours, then batteries are OK.
If time exceeds 24 hours, your batteries are excellent.

Good Luck
Michael

[Amimoto]

We have the tool and software to test battery under load or re-genitive recharge - simulating climb or going down hill (MTO will have the same system) unfortunately we are too far away.

[Bob.Kerns]

Originally Posted by Amimoto

We have the tool and software to test battery under load or re-genitive recharge - simulating climb or going down hill (MTO will have the same system) unfortunately we are too far away.

Thank you very much for posting these screenshots. It gives me a lot of context about the level of detail available. I had some concerns that the BMS on the Segway might be too old to make this info available.

I wish I had such a toy!

[jgbackes]

Originally Posted by Amimoto

We have the tool and software to test battery under load or re-genitive recharge - simulating climb or going down hill (MTO will have the same system) unfortunately we are too far away.

Does this work thought the stock Segway BMS?

I sure wish someone that likes working on this stuff would move to Silicon Valley!!! Hint Hint!!!

jeff

[Amimoto]

Originally Posted by jgbackes

Does this work thought the stock Segway BMS?

Yes it does work with all versions of stock Segway Valence BMS (AC-AH),
the example picture provided is version AF.

Also a male to female extention connector with data and power output bypass to plug into our off board fast charger so we can monitor the individual cell performance during fast charging cycle.

Thank you Bob for a simple battery and motor physics overview, you have explain it so beautifully and absolutely correct in a very easy to understand fashion.

[KSagal]

I love your 'T' connector.

I have often thought of a connector of that sort to allow two batteries (actually 4) to be in parallel, and therefore doubling the range of the segway...

I first thought of this long ago with NiMH batteries, but the concept remains valid, in that you glide with one set in the normal place, and the partner set in a bag on the segway.

I believe the extra range will more than compensate for the extra weight.

I thought that since the management of the battery itself is internal, then segway might not need much if any modifications...

Maybe even this setup could be made to work with 4 NiMH batteries instead of two LiIons, allowing for a greater range, or even an alternative to LiIons on 2nd gen machines...

[Bob.Kerns]

Originally Posted by dgbint

Hi Professor.

Easy solution.

1
Charge it up, say overnight.

2
Turn it on to get smiley face, lean it against a wall ( inside and safe where nobody can touch it ) and leave it running with nobody aboard.

3
The battery bars will go down with time, until it is flat and turns off.
If time is less than 12 hours, your batteries are weak.
If time is in the range 12-24 hours, then batteries are OK.
If time exceeds 24 hours, your batteries are excellent.

Good Luck
Michael

That's a good test of total capacity, but doesn't really address the specific case he was asking about.

Still, while they're not the same thing, internal resistance and capacity do correlate. It's a better point of reference than anything I can suggest. A good result here would certainly suggest a different issue.

[Amimoto]

Back in 2005, this Energy solution and battery management system is way ahead of its time, and it still is.
BMS's Boot loader and board firmware can be upgraded over time, individual battery cell's gain and offset can also be fine tuned to compensate the aging, it is a very advance system.
The few problems we all known of is the lack of over discharge protection circuit and the length of time battery switch to sleep (idle) mode, well, the problem is there since day one and 9 years passed..........


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