Need ideas to make simple watthour meter for ePower race

[Herrsprocket]

Hi All,

Tom here, with the ePower Challenge race (e-assist racing) out of Portland Oregon. As some of you already know, we last year hosted a new category of bicycle racing to our venue of HPV and electrathon events, the electric assist bike category. It was very cool and a lot of fun to see what the variety of e-assists could do, and believe me, there are a lot of folks who were very impressed with the performance and viabilty that e-assisting offers. So much so, that a few of the die hard recumbent racers have been inspired to add this bit technology to their steeds and hope to compete with the gang this coming year. Those same racers and several onlookers saw also the benefit of utilizing the assist features to enhance their everyday transportation needs as well. Exactly what I was hoping for ! All in all, the event served a great purpose in educating and exposing more people to the cool world of electric assist cycling and we hope to expand this venue to capture even more interest and awareness to the general public. It's all good stuff!

And as some may recall, there was some shuffling about as to how best govern and depict the guidelines for creating a "fair" playing field for all to compete on. We knew that the best solution was to somehow employ a "metering " device to attach to each vehicle and monitor their watt hour consumption, but that in this first year, it would be impossible to incorpoate such a device on such short notice and no funding to buy/ build them. The first year gave us many valuable lessons to build from and a ton of "live" performances to help us guage our guidelines.

So, what we are looking for help with is developing a very simple meter that measures and displays a watt hour reading. All the races will be predicated on the basis of watt hour useage no matter what distance, power level on board,voltage being used, etc. The meters don't "need" to have volts displayed, amps being drawn, etc. The simpler the better ( read "cost"). One readout of showing the current total watt hours cumulatively having been used should be sufficient , yes? The incorporating of this meter will allow the participant to use whatever system they wish to utilize, and also permits the racer a nice "safety" margin to not overtax the batteries ( via using a larger battery capacity level that won't jeopardize the health of the pack by draining it severely). A diverse combination of voltage, amp hours on board, etc, can all be utilized, as long as the watt hours used per race division are met.

I'm hoping to draw upon the skills and knowledge of this forum to devise an inexpensive product that can either be built with skills available from a bonehead like me, too acquiring some other entity to undertake the construction of this meter. So where to begin? Voltages "may" range from (probably) 24 volts to 72 volts, with the "reset" being done by disconnection from the system ( no reset buttons on the display,, :wink: ). I see that the watts up and doc watsons have certain voltage limits and some racers may want to run the higher voltages, as well as pretty chunky amounts of amps drawn. I may have to limit the battery voltages to 72 (or some such number) simply to keep the construction of the meter reasonable. Seem like a good place to start?

I know that there are a few nice meters out there now that can do the job( the watts up, doc's, and the CA from the super geniuses from ebike.ca, etc), but the extra features and the cost that goes with them are just too much for this fledgling event to handle. Love what they do, just need to have a much less costly solution to address our needs.

Throw me some bones, arrrf!

Tom

 

[Link]

Hmm...Unfortunately, I know of nothing suitable. You might be able to get someone to design something for you, though. Mebbe have a small production of them made if you need a lot.

 

[TylerDurden]

If $30 is do-able, DoctorBass detailed a hack to the Kill A Watt meter:

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=1428&p=24780&#p24780

 

[Herrsprocket]

Hey,

Yeah Link, I have a couple of guys up here in Portland doing a little head scratching now as for doing something cheap and original, but PLEASE, don't let that stop the other multitudes of savvy dudes out there not ponder this thing thru a bit. I just know that a few of you out there, as soon as you read this original post (things began swirling in your minds) thought," jeez, all you need to do is,," OR "seems to me you just need this layout and these components and,,". Bear in mind that with the greater success of events like this, the more folks we get involved, the better the toys get for all of us!

Thanks Tyler for the link guy. I read thru all Doc's posting and I am not quite clear on a few of the changes he made. The theory is that all the DC readings are gained (in series) from the inputs that are normally used in the AC plug ? It probably happens as Doc is sure to know how, but I'm confused as to how it is set up for seeing a voltage "across" the battery and at the same time is measuring an amperage via a shunt in series, with just two leads? I'm probably just not understanding how the meter is set up, and that's ok, I can be schooled. Once I get someone to explain it to me, then I can wrap my head around it better. Bonus too that it does have other readouts on the display if you need them, and the external power source. Doc, does this device automatically read any voltage up to ?? in DC? And does it have a limit on amps being pulled thru it?

Again, this is one possibility and I'll keep looking into this. Any other ideas out there as to how to design/construct a solution?

Thanks much folks,

Tomas

 

[Ben]

You could give an Arduino a shot.

I don't think it would be too hard to do, but it might be too expensive.

I'm pretty sure it can't accept an input greater than 5V or 1A, so you'd have to have some way of scaling voltage and a shunt.

It's a project I've been wanting to try.

 

[TylerDurden]

I read thru all Doc's posting and I am not quite clear on a few of the changes he made. The theory is that all the DC readings are gained (in series) from the inputs that are normally used in the AC plug ? It probably happens as Doc is sure to know how, but I'm confused as to how it is set up for seeing a voltage "across" the battery and at the same time is measuring an amperage via a shunt in series, with just two leads? I'm probably just not understanding how the meter is set up, and that's ok, I can be schooled. Once I get someone to explain it to me, then I can wrap my head around it better. Bonus too that it does have other readouts on the display if you need them, and the external power source. Doc, does this device automatically read any voltage up to ?? in DC? And does it have a limit on amps being pulled thru it?

I may be mistaken about DC, but I'm eager to try it. If it measures watts RMS, it might be measuring Peak-peak and DC might not pose a problem. I know the units are good up to 240V, so most EV voltages are prolly included. (PM Doc, as he may not see this thread.)

I just bought another unit to hack for my car (60V 200A), so I'll report back.

 

[Herrsprocket]

Cool, thanks Tyler. Quick Q (not to side track this thread): what kinda e-car you running,,, 60 V and 200 amp? Now back to the regular broadcast. I will PM the Doc, I figure he would respond if he knew I was asking on this thread, he's super for helping out. Yeah, maybe peak to peak for the AC and as for DC readouts, well, maybe that's what the Doc can shed some light on too. As well as the other tidbits of info, like the component switching, etc.

Someone else mentioned to me the possibility of getting CA's at a nice group buy and then offer them to the contestants to use at the race and then let them keep them. It would be nice if we could keep them, but that is a huge chunk'o dough for us to come up with. MIght be a good way for folks to get a CA for a good price, but then again, we would need to offer that purchase for participants for each year thereon. Also it was suggested that perhaps it should be a requirement for any contestant to have a watt hour meter of some kind of their own. Natch, the issue would be; could they reset the thing during the race, and is it fair to require the racers to purchase one in the first place? It's kind of cool that this thinking gets folks onboard to the idea of having a "fuel meter" as standard equipment. But does everyone want to or need to have them? It's an interesting thought, open for speculating about the future of ebikes and the growing interest in this transportation culture.

I like the idea of getting everyone to make the commitment of having them personally, but as a requirement, I'm not so sure. Sure, it would be cool if anyone shows up with their own and demonstrates that they can't monkey with them during the race, shweet. But I tend to lean towards also offering the "loan" of one of our universal meters (the ePower challenge buys them and keeps them for subsequent years of use) to those that don't have them already onboard. Just my way of thinking. But that again takes the initial purchase and leg work (research) prior to that to make it happen.

Now, these are some pretty good ideas and they may be the answer, but there are a bunch of knowledgable noggins out there who I know who have probably thought, "hmmmm , well maybe if you..." C'mon, cough up that electronic hairball, couldn't hurt!! Remember, it is for the cause, ours.

Tom

 

[Doctorbass]

8)

I smells Kill a Watt here?? :wink:


The kill a watt i s good, but without recalibrating it using the hacked procedure on the web, you will only be able to measure 15A.. higher than that will be displayed like flashing to indicate overcurrent alarm...

And yes, i was surprised to discover that they can show "DC" on the display when you put DC voltage on them.. but you will ned to suply their circuit with an external 5V power source cause at a certain low voltage under 120VAC, the AC capacitive voltage regulator will not work and with DC it will not work without the ext source.

I have the procedure to recalibrate them.. you will need an external load to put 10A at 120V for the 10A calibration..

After discovering the watts'up meter and the astroflight wattmeter for under 70$, i prefer using them... they only not indicate the power factor and reactive power and the kWh counted like the kill a watt do

Doc

 

[swbluto]

Some kind of microcontroller, with onboard ADC and the proper programming, and an LCD read-out is your most cost-effective/easiest-to-implement option(although, you could probably use multiplexed LED numeric displays for something so simple in functionality, FTW!), in conjuction with a voltage-divider for the higher-voltage folks(The finished product is the easiest to implement for low cost: And, you can also show other stats with the onboard LCD, like power, current, voltage, etc.)). The sheer component cost for small volumes, though, is probably going to be at least $15 a board and current detector but probably less than $30 so that cheap mod might be competitive.

 

[TylerDurden]

I would consider specifying a meter-port & bracket a requirement of participation: the port would accept the official meter and connect visibly and exclusively to the power source. Meters would be held by the organizing body and be randomly selected for each run.

?

 

[Herrsprocket]

Thanks guys. SW, so far so interesting, the tech is just a bit beyond what I can do, so as far as progressing or just roughly penciling ideas like this out, it will take some input from dudes like you to push it farther. If you have the time to think it thru farther, great. And if others chime in, perhaps it won't be too much for one dude to chew by himself.

TD, sounds like a good idea. Could just use simple Andersons connections. Looking at something like the Kill a Watt, that would have just the two ( I think) feeding the meter. Wouldn't that be nice. And splicing into or simply making a separate wire lead going to the meter leads would be easy. Not too expensive for the racers to accommodate the req's.

Hey Doc, how about we go off list so I can bother you for more of the details and particularly not to bother the rest of the readers with my primitive questions?

Any more ideas or thoughts, regarding new stuff or addressing these ideas already presented?

Much thanks,

Tom

 

[Herrsprocket]

Hey Doc, I've sent you a PM.

Tom

 

[Herrsprocket]

Hi Doc,

Sent you another PM. Just letting you know if you don't check your PM's too often. Thanks .

Tom

 

[safe]

Three Threads Discussing the Same Thing

Board index » General » E-vents » E BIke 101 Symposium, OHPV meeting, Portland, Oregon

http://endless-sphere.com/forums/viewtopic.php?f=25&t=7346

Board index » Electric Bicycles » E-Bike Technical » Need ideas to make simple watthour meter for ePower race

http://endless-sphere.com/forums/viewtopic.php?f=2&t=6739&hilit=need+ideas+to+make+simple+watt+hour+meters

Board index » Electric Vehicles » Battery Technology » Power Limitation Chip? (for racing)

http://endless-sphere.com/forums/viewtopic.php?f=14&t=4481&p=113534#p113534

We need a way to race while sharing the same wattage limit.

 

[safe]

Example:

Power Limit for 1000 watt class is 1000 watts, so:

Lap 1 voltage - 52 volts - Amps allowed 19.23
Lap 2 voltage - 51 volts - Amps allowed 19.60
Lap 3 voltage - 50 volts - Amps allowed 20.00
Lap 4 voltage - 47 volts - Amps allowed 21.27

...the voltage changes due to "sag", but the racing would be very, very close since the output power would be the same from start to finish. And another bike might be set up like:

Lap 1 voltage - 38 volts - Amps allowed 26.31
Lap 2 voltage - 37 volts - Amps allowed 27.02
Lap 3 voltage - 36 volts - Amps allowed 27.78
Lap 4 voltage - 32 volts - Amps allowed 31.25

...and yet both of these bikes would now race in the same class and they would perform very much the same way as their output power would be a constant.

 

[safe]

This is Important Stuff

I just want to remind the folks reading this that this is a very important circuit to develop. HerrSprocket is the guy that put together the electric bike racing at Portland International Raceway and that's a very impressive venue to display electric bikes. (we should be honored that he comes here to ask a question)

His request mirrors a request I made a while back too, that we could think about ways to develop a circuit that not just measures the wattage that a bike is using, but also restricts the bike based on some pre-configured value of watts.

So if you were to be racing in the 1000 watt class (for instance) then this circuit would guarantee that no matter what your bike setup your power would be precisely limited to 1000 watts... no more, no less... it needs to be precise to be of value.

As I see it the current side can be precisely measured with a Hall Effect Sensor that should be able to deliver accuracies in the 0%-5% range. (at most) The delivered sensor voltage is usually somewhere in a manageable scale of from between 0-5 volts with most of these sensors. (that I know of)

We need to think in terms of "averages" in both the current and the voltage because a PWM controller introduces fluxuations in the battery output that mirrors the pulses. A random sampling could produce error, so an average sampling method (or a capacitor to smooth the result) is required.

The thing I'm less clear about is the voltage side... if you have something like 72 volts how does one accurately "scale" that down to something that is manageable like 0-5 volts?

If both the current and voltage can be sampled using some kind of standardized sensor then all you would really need is a PIC chip to be able to take those scaled values and make a determination about what to do. The throttle is only 0-4 volts, so the PIC chip could do a simple "pulldown" without much trouble.

This is important folks... it deserves some serious thought and discussion...

None of the "usual suspects" like the Watts Up meter or Cycle Analyst have the ability to do more than display wattage. We need the ability to dynamically adjust the current limit based on the present value of the voltage in the battery with the effect being that wattage remains constant as the battery voltage sags.

As the voltage goes down the current limit needs to go up so as to maintain a constant wattage from the start of the race to the end...

 

[safe]

Pictures From the Race at Portland International Raceway

...the future of electric bike racing will involve the use of a "Wattage Restriction" circuit.

You could be a part of history if you contributed here.

Seriously...

Let's get the best minds on this and see what can be done.

Please post that you might be interested in helping in this historic quest... be a part of history!!!

 

[TylerDurden]

None of the "usual suspects" like the Watts Up meter or Cycle Analyst have the ability to do more than display wattage.

From http://www.ebikes.ca/drainbrain.shtml

Furthermore, the Cycle Analyst has the ability to over-ride the user's throttle and regulate the power delivered to the motor, turning an otherwise dumb ebike into an intelligent device with a user programmable speed limit, current limit, and low voltage cutout.

• Speed Limit: This has the utility of providing legal compliance to the speed cap imposed on ebikes in most jurisdictions. When used with a full throttle, it serves as a cruise control on the electric bicycle. It can also be beneficial to riders who want to increase their torque and power by using a higher voltage battery, without simultaneously increasing their top-end speed.
  
  Current Limit: An adjustable amps limit is useful to prevent damage to the batteries from excessive current draw, to increase the range that you'll get on a charge, and to protect the motor controller and motor in setups that draws too many amps.
  
  Voltage Cutout: A low voltage cutout is used to protect a battery pack from being discharged too deeply, which can cause cell reversals in NiMH/NiCad packs, permanent cell damage in Lithium packs, and sulfation in Lead Acid batteries. The programmable low voltage rollback allows you to set an appropriate low voltage point tailored to your pack.

Mods: How many times will safe be warned to not puke on others' threads...

 

[TylerDurden]

So, what we are looking for help with is developing a very simple meter that measures and displays a watt hour reading. All the races will be predicated on the basis of watt hour useage no matter what distance, power level on board,voltage being used, etc. ...
I know that there are a few nice meters out there now that can do the job( the watts up, doc's, and the CA from the super geniuses from ebike.ca, etc), but the extra features and the cost that goes with them are just too much for this fledgling event to handle. Love what they do, just need to have a much less costly solution to address our needs.

 

[safe]

Limits to Cheating

We all know that higher voltage and lower amps produces a more efficient machine than the other way around... but there are limits to this with a fixed wattage limit situation.

If you tried to run at 100 volts that means that your amp limit would be 10 amps and unless you have a specially built motor that works radically differently you will normally experience "current starvation" where the motor just never can get enough current to make use of the higher voltage.

It creates a situation where the racing is very much narrowed and the ability to cheat will be reduced a great deal because actual net wattage is under the constant supervision of this circuit.

The racing becomes more fair and more diverse at the same time!

It's really a win-win and a brilliant idea once people understand it.

 

[safe]

...I know that there are a few nice meters out there now that can do the job.

These can measure but not control based on wattage.

Herrsprocket might have made an error with that posting... no one is perfect... I don't think he even thought it out far enough to consider using the products themselves. (he was just saying he dismissed the idea out of hand based on price)

The fact remains that a true wattage restriction circuit does not exist within Watt's Up or Cycle Analyst.

Besides... think of the cheating potential...

What's to stop someone from resetting all their parameters just before the race? Is someone going to have to go through everyone's software on the starting line? And when the race promoter turns their back?

No, seriously, you need a dedicated circuit with great precision that is a true "wattage restriction" circuit and not just some digital readout.

Note:

I read back through the thread about DoctorBass "hacking" a Watt's Up meter and that looks like it might have potential. No one other than "the Doctor" seems to understand what he did (or whether accuracy can be assured) so that's just sort of out there right now. :|

If there was same way to hardcode the wattage limit into the Watt's Up meter while doing the other "hacking" then it would be usable. The wattage limit needs to be fixed.

 

[TylerDurden]

I don't think he even thought it out far enough to consider using the products themselves.

So safe is saying HairSprocket is stoopid.

M'kay...

 

[recumbent]

Okay "Safe" you made your point clear, thank you 8)

"Tyler D" give "safe" some slack, he's trying to do the right thing here, okay?

Most of us already own a CA meter and it might be easily tweeked to control the wattage, then we can just tape a cap over the button, cheating solved. Although a " wattage restriction" unit would be nice, few of us would want to spend the $30, plus the race entry fee, just for 15 minutes to race in one class.

We already know the winner will undoubtably be a faired recumbent bike with a lithium battery, & a motor turning the chain&gears will win the race.

My bike is designed for pleasure and grocery getting, but if i bolt-on a motor though the gears, I would automaticaly beat almost everyone on the track, so it's still not fair because i can afford it (if i wanted) while someone else may not.
It's still cheating as far as i'm concerned.

Can't we just have classes like 48 volts, 72 volts, and then a faired unlimited class, like Safe and a couple other people.

 

[TylerDurden]

Okay "Safe" you made your point clear, thank you 8) "Tyler D" give "safe" some slack, he's trying to do the right thing here, okay?

Matt must be very astute to know safe's intentions.

If you read the OP, the request is for a watt-hour meter.

 

[safe]

Most of us already own a CA meter and it might be easily tweeked to control the wattage, then we can just tape a cap over the button, cheating solved.

The easiest "tweek" would be to force the voltage low (below the level of the battery) to some preset constant like say 40 volts for a 48 volt bike. Then you would set the current limit to 25 amps to arrive at the 1000 watt result that is desired.

The negative about this is that you aren't getting the full voltage out of the battery. And also, you are still manually entering these values which opens the door to cheating.

Also...

I know that with SLA's there is even a "sag" difference between the front of a straight away and the end. So if you have a preset voltage limit then it has to be low enough to deal with the maximum "sag" you would encounter.

I guess the main points are:

No cheating - It needs to be impossible to mess up the restriction circuit.

Dynamic voltage and amps - Since voltage varies due to "sag" both in the short term and the long (for some battery types more than others) then you need the current limit to adapt to varying voltage. Ideally this circuit needs to work with all batteries of voltages up to about 72 volts or possibly above that level.

Note:

I did email ebikes.ca to see if they believe that the Cycle Analyst could be somehow used as a wattage restrictor and hopefully they will give us a "yes" or "no" or a "yes, if you tweek things this way" as an answer.

The main thing is that no matter if you are at the beginning or the end of the race all the time you are granted a constant wattage delivered to the motor. This will make racing very, very close and level the playing field for differing battery types.

Case in Point

http://endless-sphere.com/forums/viewtopic.php?f=25&t=7057

EV Challenge Midland Western Australia 25 Oct 08

Going to their website:

Scrutineering of non-SLA Batteries

The trial rules for the scrutineering of non-SLA batteries are as follows:

• A technical data sheet for the battery set must be submitted along with the costing sheet – by 12 th September

• Battery sets will be removed from vehicles and weighed separately, as part of scrutineering – maximum weights for non-SLA battery types will be as follows:
Nickel-cadmium – 9.6kg
Nickel-metal-hydride – 7.2kg
Lithium-ion (cobalt) – 2.9kg
Lithium-ion (manganese) – 4.3kg
Lithium-ion (phosphate) – 4.8kg

• The eV Committee reserves the right to retain any battery set for 7 days after the event, to perform discharge testing – the intent being to certify that the battery set fits within the 432W-h rating

...so you can see that everyone is struggling with some way to level out the battery playing field. This seems overly complex to have all these weird rules for different chemistries.