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 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.

[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!

[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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[Amimoto]

I forgot to mention the BMS will calculate the usage, performance (voltage and amperage), capacity of each cell bank (4 in parallel, 23 banks in series) and compensate the gain and offset to BMS, therefor adjustment is not needed during its full service life.
Only after the revive/rescue process need to re calibrate the BMS, however timing is critical with rescue, if you see red Charging LED, please ring up MTO battery ASAP for the successful revive, every additional hour passed the chance of revival diminished.


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[Amimoto]

For those who haven't seen the BMS and the cells inside the Segway battery, here you go.














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[dale@thecoys.net]

Originally Posted by Don Sparlin

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

It's a rather simple Physics problem. However, internal resistance is usually rather constant throughout almost all of battery lifetime, and often has little relationship to battery capacity.

See for instance:
http://batteryuniversity.com/learn/a...nal_resistance

http://lygte-info.dk/info/Internal%2...ance%20UK.html

But please be very careful if you actually try to do this with a Segway battery.