Battery Meters

This is the second in a series of technical articles covering some of e-bikes complexities in quite full detail so that all aspects of the subject can be appreciated.

It's impossible to accurately measure what electric current there is stored in a battery since they are chemical devices, the electricity existing in a different form as a change of chemical state.

Therefore, what these battery meters on our bikes do is use the fact that a battery voltage declines very slightly as it discharges. They check the voltage coming from the battery and register it's level on the LED lights. This isn't very accurate but gives a rough idea of the state of charge when a bike is standing still.

The problem comes when riding though. If the throttle is opened and the motor runs, it draws current and the voltage coming from the battery drops due to the increased load drain, and the LED lights reflect this drop in voltage. On a steep hill when the motor is working very hard, the drain of current is greatest, the voltage drop is also greatest, so the red or lowest light can come on.

The only way to measure the battery content on these meters when riding is if you shut the throttle and stop pedalling for a moment and then look at the meter, though it's still not precise then.

Some owners use the battery meter as an economy meter while riding, trying with careful throttle use to avoid the lights dropping and so get better range, but it's fiddly doing this. If this type of usage is intended, it's better to buy one of the rather expensive (£50 to £100) consumption meters like the "DrainBrain" (now known as the CycleAnalyst) or "WattsUp". These measure the current being used while riding and can assess what the battery had in it once all the current is used. It's then possible to predict with some accuracy in future the remaining content in a battery, and this type of meter is also very easy to use to monitor consumption as you ride, and thus keep it low to get the best range.

There's no economic case for using these though, since the minute saving in charge current which could be achieved by careful riding with one could mean it would take around 10 to 24 years to recover the cost of the consumption meter, so they have the status of executive toy for most users, good fun but of limited practical use. Bicycle testers and reviewers find them invaluable of course.

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Edited November 14, 201015 yr by flecc

This is the second in a series of technical articles covering some of e-bikes complexities in quite full detail so that all aspects of the subject can be appreciated.

 

It's impossible to accurately measure what electric current there is stored in a battery since they are chemical devices, the electricity existing in a different form as a change of chemical state.

 

Therefore, what these battery meters on our bikes do is use the fact that a battery voltage declines very slightly as it discharges. They check the voltage coming from the battery and register it's level on the LED lights. This isn't very accurate but gives a rough idea of the state of charge when a bike is standing still.

 

The problem comes when riding though. If the throttle is opened and the motor runs, it draws current and the voltage coming from the battery drops due to the increased load drain, and the LED lights reflect this drop in voltage. On a steep hill when the motor is working very hard, the drain of current is greatest, the voltage drop is also greatest, so the red or lowest light can come on.

 

The only way to measure the battery content on these meters when riding is if you shut the throttle and stop pedalling for a moment and then look at the meter.

 

Some owners use the battery meter as an economy meter while riding, trying with careful throttle use to avoid the lights dropping and so get better range, but it's fiddly doing this. If this type of usage is intended, it's better to buy one of the rather expensive (£50 to £100) consumption meters like the "DrainBrain" or "WattsUp". These measure the current being used while riding and can assess what the battery had in it once all the current is used. It's then possible to predict with some accuracy in future the remaining content in a battery, and this type of meter is also very easy to use to monitor consumption as you ride, and thus keep it low to get the best range.

 

There's no economic case for using these though, since the minute saving in charge current which could be achieved by careful riding with one could mean it would take around 10 to 24 years to recover the cost of the consumption meter, so they have the status of executive toy for most users, good fun but of limited practical use. Bicycle testers and reviewers find them invaluable of course.

.

I appreciate that the yellow light comes on when under pressure on a steep hill but yesterday it remained on after I have ceased to use the throttle and did not revert to green until I had switched off and the on again? Am I still draining the current? I ride a eZee Sprint.

That's correct Jill, the yellow indicating the amount left in the battery when you had the throttle off, the proper meter function, not influenced by the motor. In other words, you didn't have much charge left in it, the exact distance left depending on territory etc.

Li-ion batteries do have some degree of chemical recovery though, and in switching off and on, you'd helped that to happen. If you'd been in a situation where you could have parked at that moment, some while later it would probably have returned to green for longer due to the very slight recovery of charge.

This happens because this type find it difficult to get the charge out quickly enough when the demand is high, and a chemical blockage occurs and builds up. When the battery is rested, the blockage disperses and allows a better flow of current, returning the meter to green for a little while longer.

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Edited October 31, 200718 yr by flecc

Power consumption 'meter'

I am working on a new meter that measures voltage (a simple static guide), Amp/hours consumed since recharge (aka coulomb-counting) and has an audible feedback on the actual current being consumed.

Coulomb-counting is a good measure, but you need to calbrate it as the battery tails off over charge cycles. That can be done dynamically by storing how many Amp/hours came out between maximum voltage (when freshly charged) and when the controller cuts out (usually 30V or 20V depending on battery nominal voltage)

The 'proper' way to measure charge state is to measure its impedance - how its terminal voltage changes with load, and so the intuitive way is to ride trying to keep out of the Amber!

The audible feedback (akin to the ticking of a freewheel) is intended to help the rider manage the power without looking away from the road! The voltage measurement gives some idea of charge state without actually sucking power (SLA, NiMh and LiIon all exhibit falling voltage with charge.

I remember my Father had a vacuum gauge on the inlet manifold of his Hillman car and drove to achieve least depression - I had a Jag. with an 'econometer' that did just the same, but why would you want that on a 3.2S!!!

I am a reformed character now....

I have an old Panasonic battery that I have not used for over a year.It is almost 5 years old.I stopped using it for my lafree because it was not lasting very many miles.

I have 2 more recent batteries which I have been using frequently for my 22 miles round commute.

For interest sake I recharged the old battery from scratch,to see if there was any life left in it.To my amazement it now travels over 50% more than it used to do.What is the explanation?

Julian Langer

That's very unusual Julian. It's more usual for an NiMh battery to refuse to accept a charge if it's been left months without a charge and the cell voltages have dropped to very low levels. However, that's not an absolute.

I think what might have happened in your case is that the hydrate has recovered and normalised without losing all it's hydrogen content, that enabling a recharge.

NiMh are actually a form of fuel cell, but a closed circuit one. The fundamental principle of their working is that charging hydrolyses water, turning it into free oxygen and hydrogen which combines with rare earths, forming the hydrate.

When connected to a load, the hydrogen is released from the hydrate and recombines with the free oxygen, releasing the stored electrical energy. Your rested and revitalised hydrate has given you more range, but it might be a bit early to celebrate it since the gain might be very short lived, returning to the short range you had before, or even less.

.

I am working on a new meter that measures voltage (a simple static guide), Amp/hours consumed since recharge (aka coulomb-counting) and has an audible feedback on the actual current being consumed.

 

Coulomb-counting is a good measure, but you need to calbrate it as the battery tails off over charge cycles. That can be done dynamically by storing how many Amp/hours came out between maximum voltage (when freshly charged) and when the controller cuts out (usually 30V or 20V depending on battery nominal voltage)

 

The 'proper' way to measure charge state is to measure its impedance - how its terminal voltage changes with load, and so the intuitive way is to ride trying to keep out of the Amber!

 

The audible feedback (akin to the ticking of a freewheel) is intended to help the rider manage the power without looking away from the road! The voltage measurement gives some idea of charge state without actually sucking power (SLA, NiMh and LiIon all exhibit falling voltage with charge.

 

I remember my Father had a vacuum gauge on the inlet manifold of his Hillman car and drove to achieve least depression - I had a Jag. with an 'econometer' that did just the same, but why would you want that on a 3.2S!!!

 

I am a reformed character now....

Hi

how did the meter pan out..I would love one for my Aguattu in ageeky way,

BUT would like one for my electric outboard moter on a folding mirror dingy. I have done some really stupid things with boats and bikes, but now Lady J often accompanies me in the boat, I don't take any risks..the motor draws from 10 to 25 amps from 2 55ah gels, depending on speed (controlable) but wind conditions, uncontrollable over maybe a day out on the lake, sea..see the problem

Thanks in advance Oldosc

This is the second in a series of technical articles covering some of e-bikes complexities in quite full detail so that all aspects of the subject can be appreciated.

 

It's impossible to accurately measure what electric current there is stored in a battery since they are chemical devices, the electricity existing in a different form as a change of chemical state.

 

Therefore, what these battery meters on our bikes do is use the fact that a battery voltage declines very slightly as it discharges. They check the voltage coming from the battery and register it's level on the LED lights. This isn't very accurate but gives a rough idea of the state of charge when a bike is standing still.

 

The problem comes when riding though. If the throttle is opened and the motor runs, it draws current and the voltage coming from the battery drops due to the increased load drain, and the LED lights reflect this drop in voltage. On a steep hill when the motor is working very hard, the drain of current is greatest, the voltage drop is also greatest, so the red or lowest light can come on.

 

The only way to measure the battery content on these meters when riding is if you shut the throttle and stop pedalling for a moment and then look at the meter.

 

Some owners use the battery meter as an economy meter while riding, trying with careful throttle use to avoid the lights dropping and so get better range, but it's fiddly doing this. If this type of usage is intended, it's better to buy one of the rather expensive (£50 to £100) consumption meters like the "DrainBrain" (now known as the CycleAnalyst) or "WattsUp". These measure the current being used while riding and can assess what the battery had in it once all the current is used. It's then possible to predict with some accuracy in future the remaining content in a battery, and this type of meter is also very easy to use to monitor consumption as you ride, and thus keep it low to get the best range.

 

There's no economic case for using these though, since the minute saving in charge current which could be achieved by careful riding with one could mean it would take around 10 to 24 years to recover the cost of the consumption meter, so they have the status of executive toy for most users, good fun but of limited practical use. Bicycle testers and reviewers find them invaluable of course.

.

Disagree with your last point here. The electricity saved would seem to be the least of the economic advantages. Extended range, extended battery life (especially on kits or home builts) and not running out 5 miles from home would all help.

It's a bit like a car without a fuel gauge. Sure you can get a good idea for range, but...

Disagree with your last point here. The electricity saved would seem to be the least of the economic advantages. Extended range, extended battery life (especially on kits or home builts) and not running out 5 miles from home would all help.

 

It's a bit like a car without a fuel gauge. Sure you can get a good idea for range, but...

Extended range is arguably an economic point if one wants to ride in that manner all the time, constantly monitoring, but many would consider it a miserable way to an e-bike.

Actually these meters are even less useful now that lithium batteries are so universally used. Since most user's journeys are well within the range of their bikes and recharging every trip is desirable with these batteries, the only possible gain for them is in the current saving, which as said is too small to bother with. Extended battery life is very questionable with lithium batteries where all current types on commercial bikes have their life determined by age as much as anything else, and usage is only at the top end of the charge range for many, the cells never discharging fully.

I'm think most e-bike users would find the information interesting at the outset and then get bored with it and just carry on as before.

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Edited May 18, 200916 yr by flecc

hmm.

If one buys a bike with a large battery capable of high C rates (higher than the motor draws) and the normal riding pattern is considerably less than the whole range, I'd agree with you. It seems that this would be the case with many of the bikes available in Britain.

Still over on endless sphere, most there are far more positive on Cycle Analysts and the like. I think this is due to the higher percentage of conversion kits being used, long ranges at higher speeds and the potential for the common Crystalyte motors to draw far more current at stalls than a lot of batteries will gracefully put out.

I'm probably going to get a Cycle Analyst myself, when I eventually get back to NZ and need to buy an ebike (right now I'm pushbike only, motorbike in the past.)

We're solely limited by power here (300W) not by requirement to pedal, speed or anything else. I can get a Nicd/NiMH conversion kit with a cycle analyst for roughly $1600NZ, and a good second hand steel bike for it for a few hundred, while a Wisper or Ezee will cost $3000. Of course the Wisper has the better battery and style. But the conversion kit will have more power. I could also get the NA Ezee kit which is a bit more powerful than the Ezee bikes available in NZ (Europe models).

If I go such a route then I will probably need the CA to:

a) limit current to the 300W legal maximum.

b) make sure that I'm not using my system inefficiently and all the parts are playing nice. i.e I'm not draining a 2c battery at 5c going up a hill.

c) keep track of cycle and battery life (done automatically)

d) brag online about my Wh/km statistics

e) Act as a backup to the low voltage cutout on the controller or BMS. For the Nicads or NiMh there is no BMS and then the Low voltage feature becomes important.

They also have data logging functions, regen calculators and other stuff I won't need.

As you said they are great for testers and reviewers. To this I'd add that they're great for hobbyists, long range riders* and for managing conversion kits or DIY bikes. If you buy a well put together bike with well matched components, and you ride it well within it's capabilities, then you're absolutely correct. There isn't a strong economic case.

*The inventor of the Cycle analyst rode an ebike coast to coast across Canada last year. I don't think one could do this easily without a proper way of measuring range.

I fully agree with all this, and as you say, it must have been very useful on Justin's coast to coast ride.

I basically write for this forum which is very much a mainstream consumer forum, while Endless Sphere is very performance biased with thirsty beasts like the Crystalyte motor and other kits being commonly used. I can only remember two members here buying Crystalytes, one for off road racing and the other got rid of his in favour of a less powerful more refined motor.

So the two forums are very different and complementary, a bit like Performance Car and What Car magazines.

I didn't know NZ had a 300 watt limit, rather more liberal than Australia's 200 watt, and it's good that you'll only have that one regulation to worry about. Here we know that we are going lose the throttle only facility in due course and will subsequently be confined to the 15 mph/250 Watt/pedelec only systems.

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I'd get a crystalyte if I could trust the build quality. Problem with being in such a small market as NZ is that no products are designed for us. Doubly so for already niche products like ebikes.

That's true. I suppose one of the nearest to suitability for power on the high side with a decent battery and NZ support is Wisper with agent Anthony at Electric Bikes NZ, Domain Road, Whakatane.

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That's true. I suppose one of the nearest to suitability for power on the high side with a decent battery and NZ support is Wisper with agent Anthony at Electric Bikes NZ, Domain Road, Whakatane.

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Yes Electric bikes NZ seems to be a very good shop. He doesn't have quite what I'm looking for yet though. The Elation kit seems good, but I don't really want a chain drive. It's good for extreme speeds, and off road hill climbing but I'm not planning to do that. $3000 for a Wisper 905se, or $2000 for the 905eco is pretty good but I can get a kit for less. The main reason why I'm not really considering the Wisper is the certain knowledge that I'd be replacing the battery in 2 or 3 years. One of the things I have in mind is that I need to convince my wife that these things are dirt cheap- so she'll get one herself. If they had a LiFePO4 battery, I'd pull the trigger on them.

Here's another kit I'm considering. No Cycle Analyst or meter on them, but thinking about what you've said with 36v15Ah of LiFePO4, I may not need it.

High Tech Bikes

Just need to find a 300w sticker to put on it now!

/derail.

Edited May 21, 200916 yr by OneWayTraffic

That's quite a motor, very much like the Crystalytes. It really needs steel forks though, and preferably an anti-torque plate to make sure it doesn't spin in the dropouts and come out of the forks.

It would be fun though.

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i find my watts up meter very usefull for fault diagnosis. if my bike brakes down during a ride, as it often does because its DIY, then i want some thing to tell me whats going wrong. sometimes the watts up meter will give me the clue i need to fix it there and then.

also its invaluable to make sure your not thrashing your expensive batteries. i spent £600 on batteries. i'm happy spending £30 to know i'm not miss treating them.

Metering is by the same method for all battery types BBB, measuring the fractional decline in the voltage as the battery empties. The voltage decline characteristic varies a little with each battery type, so one from a lithium batteried bike would not be a good match for a bike with lead acid batteries.

However, since they are all fairly inaccurate some interchangeability is possible, the readings not necessarily being linear though.

I don't know of any truly generic meters for any battery kind, each bike manufacturer fits their bikes with one to suit, often run off the controller.

.

Thanks for the reply, but I wondered about a bench type battery tester.

Do some suppliers use these.

I can only remember two members here buying Crystalytes, one for off road racing and the other got rid of his in favour of a less powerful more refined motor.

There's now Herb's recent Brompton DIY job

http://www.pedelecs.co.uk/forum/electric-bicycles/5031-brompton-crystalite-209-motor-3.html#post65179

Thanks for the reply, but I wondered about a bench type battery tester.

Do some suppliers use these.

I don't know offhand if any suppliers use them. The trouble with sealed lead acid types is that only a voltage or capacity drain test is really possible, testing of individual cells and electrolyte specific gravity isn't possible. A multimeter can check the voltage and the performance on the bike is an adequate capacity drain test so any other kind of bench meter seems to have no point

For the fullest information you could use an expensive Cycle Analyst or Watts-Up meter of the kind referred to within this thread, but I'm not sure what you want to achieve here?

.

 

I can only remember two members here buying Crystalytes, one for off road racing and the other got rid of his in favour of a less powerful more refined motor.

There's now Herb's recent Brompton DIY job

 

http://www.pedelecs.co.uk/forum/electric-bicycles/5031-brompton-crystalite-209-motor-3.html#post65179

Not back in May 2009 when I posted that though!

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For the fullest information you could use an expensive Cycle Analyst or Watts-Up meter of the kind referred to within this thread,

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Quite a few alternatives to the Watts-Up in this thread:

http://www.pedelecs.co.uk/forum/electric-bicycles/4821-watts-up-vs-turnigy-power-meter-analyser.html?highlight=watt+meter#post60953

...although personally I find that the Cycle Analyst is an essential tool to monitor the energy consumption patterns of my e-bike.

++ Dan