Some thoughts on Segway Batteries

[Isidore]

As I've mentioned in another thread, I'm having problems with one i2 battery that ends it's charge cycle with a red light. I took the batteries off yesterday to check which production series they are (AE) and I also intended to check the battery voltages with a voltmeter to see what differences I could find between units and between the two cell packs in each unit.

If you look at the terminals in the connector of a Segway battery, you have a bunch of small pins which I assume are to do with powering the internal charger in the battery and probably monitoring the battery state, and in the middle, you have four larger terminals which are the ones that actually feed power to the Segway. This is where things go slightly wrong in my description. In an old NiMH battery you have four 'power' terminals (each battery is actually marked as 2 cells at 36 volts) and on the connector on the base of the Segway (gen 1 or gen 2) you have corresponding connectors going into the power circuit. BUT, my i2 batteries actually only have two pins of the four with copper connectors. Across these you see about 79 volts. What is going on? The base seems to be wired to have each battery pack connected to it as two separate batteries, but the batteries are actually wired internally as one large 79 volt cell. I'm clearly missing something. Also, is this the reason why an i2 cannot use the early lithium batteries from a gen 1, the change in battery wiring?

Can anyone shed light on what the changes were and why they were done?

[bystander]

As I've mentioned in another thread, I'm having problems with one i2 battery that ends it's charge cycle with a red light. I took the batteries off yesterday to check which production series they are (AE) and I also intended to check the battery voltages with a voltmeter to see what differences I could find between units and between the two cell packs in each unit.

If you look at the terminals in the connector of a Segway battery, you have a bunch of small pins which I assume are to do with powering the internal charger in the battery and probably monitoring the battery state, and in the middle, you have four larger terminals which are the ones that actually feed power to the Segway. This is where things go slightly wrong in my description. In an old NiMH battery you have four 'power' terminals (each battery is actually marked as 2 cells at 36 volts) and on the connector on the base of the Segway (gen 1 or gen 2) you have corresponding connectors going into the power circuit. BUT, my i2 batteries actually only have two pins of the four with copper connectors. Across these you see about 79 volts. What is going on? The base seems to be wired to have each battery pack connected to it as two separate batteries, but the batteries are actually wired internally as one large 79 volt cell. I'm clearly missing something. Also, is this the reason why an i2 cannot use the early lithium batteries from a gen 1, the change in battery wiring?

Can anyone shed light on what the changes were and why they were done?A voltmeter is a very basic tool to use on the Saphions. A very basic tool. It can only tell you the open circuit voltage. It won't tell you the current capacity, it won't tell you the nominal voltage during charge and discharge, and it won't tell you the internal resistance. It also doesn't give a good idea of internal pack temperature during use.

Comparing a good pack with a bad back with only a voltmeter may not tell you anything meaningful. Results can be inconclusive due to not being able to tell what's really going on during the charging and discharging process.

Unfortunately the tools that would tell you such things are rather expensive. The PT has built-in instruments to measure all that stuff, but since it isn't "open-source", there isn't a practical way to interrogate the PT on what it knows.

79 volts is a typical open-circuit voltage to measure on the Saphion packs, the nominal voltage being 73.6 v. Each of the two control unit (CU) boards inside the PT use 72 volts nominal, (or so). Each NiMH pack has two 36 v nominal sub-packs that become wired in series when connected to the bottom of the PT, for a total of 72 v nominal for each CU board. When the NiMH packs are off the PT, a voltmeter will confirm the existence of two 36 v nominal packs. The actual voltage read on NiMH will vary with how well it's charged and temperature. I recall reading reports of 34 to 39 volts or so, measured open-circuit with a voltmeter.

A consumer's least expensive way to check the batteries capacity is to monitor the charging progress after a full discharge. This can be done by keeping an eye on it, or setting up the camcorder or webcam trained on the charge progress LEDs (and a clock in the same frame) and reviewing it later.

The normal sequence is when the batteries advance through the charging process at the same pace as each other, and take about 8 -10 hours to finish charging.

If you observe one or both batteries significantly more or less time to complete, then something is definitely wrong.

Another way for a consumer to inexpensively measure the capacity of the Saphion packs is to get one of those "kill-a-watt" meters and measure how much total energy accumulates in the pack when charging after a full discharge. A new set of Saphion packs will "eat" over 1000 watt-hours of energy, as the capacity is over 800 kwh (200 or so wh for the charger). It's hard to tell the exact amount due to charging efficiency and various variable conditions. The best thing to do is to compare against a baseline made with a new set of packs, or at least a baseline with a set of packs that aren't showing troubles.

My pair of Saphions, now two years old, "eat" less than 1000 wh on a full charge when I measure them on the "kill-a-watt" meter. They also get less range than when they were new, but no dramatic losses yet.

Here's a link to the "kill-a-watt" page:

http://www.p3international.com/products/special/P4400/P4400-CE.html

This seems to be the equivalent for use in the UK:

http://www.maplin.co.uk/Module.aspx?ModuleNo=38343

Lastly, the reason that gen2s can't use early gen1 Saphions is due to internal firmware differences in the charging controller on the PCB inside the packs. The wiring is 100% compatible. We've been told that the firmware can be re-programmed to be compatible, but such things only seem to be accomplished at HQ, this kind of re-programming is not offered at dealers.

[Isidore]

Thanks bystander, I appreciate your comments. I am aware that without measuring the voltage under load I am not measuring very much- it was just a first step reading to look for any gross failure. A watt meter is a good idea and will try to get one from maplins- they have a shop very close to me. I think you have indirectly answered my main question on this which was why only two power terminals instead of 4. I assume that the series connection now occurs in the battery rather than in the platform. I had sort of assumed that as part of the system redundancy that each of the controller boards was fed from half of each battery but what you describe makes more sense. Having put the batteries back in a different position from the one before, the red light has also switched location so time for a talk with the UK importer.....

[polo_pro]

Lastly, the reason that gen2s can't use early gen1 Saphions is due to internal firmware differences in the charging controller on the PCB inside the packs. The wiring is 100% compatible. We've been told that the firmware can be re-programmed to be compatible, but such things only seem to be accomplished at HQ, this kind of re-programming is not offered at dealers.

My understanding was that at least one person had gotten this upgraded for their old Li-Ions by sending the batteries to Segway INC in NH. So it's possible...I didn't hear how much he was charged though for this service. When this happened, I'm not too sure. I know it was after the i2 release, but I don't remember if it was just before (or just after) Segfest 2006.

If there is a future Segfeset (or big glider get together with hundreds of people at the same place as a bunch of Segway INC employees), it'd be a GREAT opportunity for Segway INC to offer battery upgrades. I know it'd potentially eat into future battery sales, but customers would have some assurance that Segway INC was trying to preserve their investment in batteries.

From another perspective, as handlebars break and Gen 1 owners have to face the fact they have to sell their segway for parts (rather than pay what will soon be $1000 for new handlebars), being able to salvage/liquidate their batteries as they move up to an i2 will soften the blow. Think of it as Segway INC doing their part to increase your "trade in value". Perhaps sales of off board chargers (OBC) will go up?

[bystander]

Thanks bystander, I appreciate your comments. I am aware that without measuring the voltage under load I am not measuring very much- it was just a first step reading to look for any gross failure. A watt meter is a good idea and will try to get one from maplins- they have a shop very close to me. I think you have indirectly answered my main question on this which was why only two power terminals instead of 4. I assume that the series connection now occurs in the battery rather than in the platform. I had sort of assumed that as part of the system redundancy that each of the controller boards was fed from half of each battery but what you describe makes more sense. Having put the batteries back in a different position from the one before, the red light has also switched location so time for a talk with the UK importer.....One NiMH battery pack of a total of 60 NiMH cells, wired in series. This can be easily split into two equal parts. It might have been designed that way for more flexible charging solutions early on, but was never fully utilized. The "charger" in the CSB and the off-board charger (they're not really chargers, just power supplies) use current-limited 100v power to accomplish charging. By halving the battery, a 50 v charger could be used. But in practice, such a charging system hasn't been made public.

It's also possible that the "split" pack design may have been done initially for safety or certification reasons, back in the early stages of the design process, and got left in. The packs connect directly to the CU boards, for minimal electrical losses, so pack design is somewhat tied to CU board design.

One Saphion pack has 92 Saphion cells. This number, 96, is easily split in to two equal parts, but the Saphion pack does not have the 96 cells wired in series. The nominal voltage of a single Saphion cell is 3.2 v. 73.6, (the nominal voltage of the Saphion pack), divided by 3.2 equals exactly 23. This means there are 4 cells wired in parallel at each step, with a total of 23 steps in series. 4 x 23 = 92. 23 does not evenly divide into two equal integer parts, so it's configuration is as a single 73.6 v device, rather than being split up into two parts.

Each CU board is exclusively connected to a single pack, but the power applied to the motors is shared from both boards. This is accomplished by having two sets of windings in each motor, one set being driven by each CU board. The motors are three phase, so there are a total of 12 windings. Coincidentally, there are 12 power FETs altogether, six on each CU board.

[bystander]

If there is a future Segfeset (or big glider get together with hundreds of people at the same place as a bunch of Segway INC employees), it'd be a GREAT opportunity for Segway INC to offer battery upgrades. I know it'd potentially eat into future battery sales, but customers would have some assurance that Segway INC was trying to preserve their investment in batteries.
I agree with you on the "assurance" angle.

An inquiry was made before Segfest 2006 as to whether Segway, Inc. could offer the Saphion firmware upgrade at the fest. But with all the other things going on (recent PT recall at that time), they were not able to.

[polo_pro]

It's also possible that the "split" pack design may have been done initially for safety or certification reasons, back in the early stages of the design process, and got left in. The packs connect directly to the CU boards, for minimal electrical losses, so pack design is somewhat tied to CU board design.

<math snipped>

Each CU board is exclusively connected to a single pack, but the power applied to the motors is shared from both boards. This is accomplished by having two sets of windings in each motor, one set being driven by each CU board. The motors are three phase, so there are a total of 12 windings. Coincidentally, there are 12 power FETs altogether, six on each CU board.

Is it possible the fault tolerant design intend to use the "good half" of a battery if one half shorted out? In situations where both batteries are almost drained, this might be the difference between keeping both wheels moving or not.

Effectively splitting each battery into half could give you 4 different power sources, right? That's about as good as it gets when it comes to fault tolerant designs!

[bystander]

Is it possible the fault tolerant design intend to use the "good half" of a battery if one half shorted out? In situations where both batteries are almost drained, this might be the difference between keeping both wheels moving or not.

Effectively splitting each battery into half could give you 4 different power sources, right? That's about as good as it gets when it comes to fault tolerant designs!The halves would have to be combined in parallel instead of series for something like what you suggest to work.

This is not as efficient, because there are more losses in a 36 v motor circuit than a 72 v motor circuit, plus losses occur when adding switching (either mechanical or electronic) to combine the batteries in parallel, if you still want to be able to disconnect a "faulty" one.

Also, the four batteries separately would have less current on their own, so the PT would probably fall over if just operated on one.

So I would have to say that you have come up with a more faulty design than a more fault tolerant design, sorry.

[Mr_Laurenzano]

My offboard charger is smoldering...more more more. :D

[Isidore]

One NiMH battery pack of a total of 60 NiMH cells, wired in series. This can be easily split into two equal parts. It might have been designed that way for more flexible charging solutions early on, but was never fully utilized. The "charger" in the CSB and the off-board charger (they're not really chargers, just power supplies) use current-limited 100v power to accomplish charging. By halving the battery, a 50 v charger could be used. But in practice, such a charging system hasn't been made public.

It's also possible that the "split" pack design may have been done initially for safety or certification reasons, back in the early stages of the design process, and got left in. The packs connect directly to the CU boards, for minimal electrical losses, so pack design is somewhat tied to CU board design.

One Saphion pack has 92 Saphion cells. This number, 96, is easily split in to two equal parts, but the Saphion pack does not have the 96 cells wired in series. The nominal voltage of a single Saphion cell is 3.2 v. 73.6, (the nominal voltage of the Saphion pack), divided by 3.2 equals exactly 23. This means there are 4 cells wired in parallel at each step, with a total of 23 steps in series. 4 x 23 = 92. 23 does not evenly divide into two equal integer parts, so it's configuration is as a single 73.6 v device, rather than being split up into two parts.

Each CU board is exclusively connected to a single pack, but the power applied to the motors is shared from both boards. This is accomplished by having two sets of windings in each motor, one set being driven by each CU board. The motors are three phase, so there are a total of 12 windings. Coincidentally, there are 12 power FETs altogether, six on each CU board.

Very interesting. If each stage of the pack has 4 cells in in parallel, what would give me a red light at the end of charging and the other symptoms I am seeing, poor performance and a definite fall off in range. I don't imagine that I have more than one or possibly two substandard cells and if there are 4 cells in parallel this will give some voltage drop and increase in internal resistance but I would imagine it to be quite small. I suppose if the bad cell is effectively shorting out one stage that would probably do it. Just don't know enough about complex cell packs to work it out.

[bystander]

Very interesting. If each stage of the pack has 4 cells in in parallel, what would give me a red light at the end of charging and the other symptoms I am seeing, poor performance and a definite fall off in range. I don't imagine that I have more than one or possibly two substandard cells and if there are 4 cells in parallel this will give some voltage drop and increase in internal resistance but I would imagine it to be quite small. I suppose if the bad cell is effectively shorting out one stage that would probably do it. Just don't know enough about complex cell packs to work it out.Pretty much all speculation is moot, as the packs are sealed and not intended for anyone to replace any cells, whether it be the end user or the manufacturer. You could have one bad stage, or a dozen bad stages, you may never know for sure.

The red LED indication is that the internal processor in the pack has determined that there is a charging malfunction.

There may have been only one bad cell or stage, or no bad cells at all, and malfunctioning charging circuitry damaged a cell or cells over time.

If you're getting a typical open circuit voltage across the pack, there may not be any shorted cells. The internal diagnostic in the pack may be indicating an error for any number of reasons, such as excessive current in one or more stages, or internal overheating during charging. Maybe the internal cell balancers indicate that one or more of the stages cannot be balanced within the expected limits for safe operations.

[NovaScotian]

Interesting topic. My i2 is almost a year old, and my front LED battery charging indicator turns solid red soon after the charge cord is plugged in. The first time this happened my i2 was about 1 week old. I removed both batteries and reinstalled them. All was good for about 4 months. When it happened again the front LED was solid red. I removed both batteries and re-installed rotating front to back and back to front; thinking if it were to happen again, the back LED should become solid red next time. Last month, the front LED again was solid red. Regardless of my battery position, only the front LED glows solid red, which leads me to believe it is not an indication of the battery’s performance, but rather some controller circuit board inside the i2.

Since the batteries can either be removed and reinstalled to their original position or rotated, either method seems to correct my front red LED problem. My theory is; the i2 circuitry can lockup and require a reboot, just like any computer. By temporarily removing the power source, you force a hard reboot on the i2.

[SEGsby]

I would talk to your dealer and see if you can't get that repaired before warrenty expires.

SEGsby

Interesting topic. My i2 is almost a year old, and my front LED battery charging indicator turns solid red soon after the charge cord is plugged in. The first time this happened my i2 was about 1 week old. I removed both batteries and reinstalled them. All was good for about 4 months. When it happened again the front LED was solid red. I removed both batteries and re-installed rotating front to back and back to front; thinking if it were to happen again, the back LED should become solid red next time. Last month, the front LED again was solid red. Regardless of my battery position, only the front LED glows solid red, which leads me to believe it is not an indication of the battery’s performance, but rather some controller circuit board inside the i2.

Since the batteries can either be removed and reinstalled to their original position or rotated, either method seems to correct my front red LED problem. My theory is; the i2 circuitry can lockup and require a reboot, just like any computer. By temporarily removing the power source, you force a hard reboot on the i2.

[bystander]

Interesting topic. My i2 is almost a year old, and my front LED battery charging indicator turns solid red soon after the charge cord is plugged in. The first time this happened my i2 was about 1 week old. I removed both batteries and reinstalled them. All was good for about 4 months. When it happened again the front LED was solid red. I removed both batteries and re-installed rotating front to back and back to front; thinking if it were to happen again, the back LED should become solid red next time. Last month, the front LED again was solid red. Regardless of my battery position, only the front LED glows solid red, which leads me to believe it is not an indication of the battery’s performance, but rather some controller circuit board inside the i2.

Since the batteries can either be removed and reinstalled to their original position or rotated, either method seems to correct my front red LED problem. My theory is; the i2 circuitry can lockup and require a reboot, just like any computer. By temporarily removing the power source, you force a hard reboot on the i2.You seem to be on the right track. The red LED indicator indicates a problem with the overall charging system, whether it be a pack or the power supply inside the i2.

In your case, the position of the red LED indicator does not move when you swap packs, implicating a fault of some kind in the powerbase. As SEGsby notes, you may want to have that looked at, as some posters have indicated that it's possible for a faulty powerbase to eventually damage the batteries over time.

[NovaScotian]

Thanks SEGsby and bystander. I just spoke with Segway Tech-Support again on this issue. They have opened a waranty service order for me, since my warranty will expire in 2 days! They seem to think the problem is likely within the charge circuitry of the power base. I also mention my Wheel Wobble and my fix by rotation of the wheel by one lug. They noted that as well on the service order, saying that only masks the problem, not correcting it. So double bonus in warranty repairs!

Thanks again.

[bystander]

Thanks SEGsby and bystander. I just spoke with Segway Tech-Support again on this issue. They have opened a waranty service order for me, since my warranty will expire in 2 days! They seem to think the problem is likely within the charge circuitry of the power base. I also mention my Wheel Wobble and my fix by rotation of the wheel by one lug. They noted that as well on the service order, saying that only masks the problem, not correcting it. So double bonus in warranty repairs!

Thanks again.You're welcome. Glad to be of help.

Er, if you've got a minute and haven't shipped that i2 yet...

Could you remove a wheel and measure the thickness of the flange on the gearbox that holds the 3 bolts for the wheel?

And then when you get it back, do the same and see if the replacement is slightly thicker?

Just curious here, don't go to any extra trouble on my account.

[Isidore]

I would really also like to know if the flange thickness changed. I had a replacement base as a result of a serious wheel wobble in January. I had a loss of traction fall in which the seg did not cartwheel or hit anything and I ended up with a huge eccentricity on one wheel. Took a lot of dial gauge readings ( and posted them in a thread at that time) I am curious if they increased the material thickness of the flange or perhaps changed the heat treatment to reduce the ease of plastic deformation of the steel plate. Forgot to measure the 'before' thickness before sending the platform back to Italy...