amberwolf wrote: ↑Jan 11 2018 1:17pmHow efficient is the motor at a particular speed/voltage? (see the manufacturer for the curve chart, or experiment with it on the http://ebikes.ca/simulator if yours is listed there)
That will tell you that if you run it at a particular speed, then you'll get about that voltage out at about that efficiency, depending on the load you put on it (because in general a motor will work as a generator with about the same efficiency).
I can't change the efficiency of the gas motor; only seek (through gearing appropriately) to run it at its most efficient rpm.amberwolf wrote: ↑Jan 11 2018 1:17pmThis efficiency is only part of the equation--you also have the low efficiency of the ICE to start with (though it'll be better than otherwise since it'll be running mostly at one speed, so you can just set it up to run at the speed it's best at, and gear it down or up to drive the motor/generator).
I must admit I thought that a suitable, regen capable controller would take care of rectification and current limiting; and a BMS would prevent overvolting. If that is not the case, it makes me wonder what is to stop regen from wrecking your batteries on a long descent?amberwolf wrote: ↑Jan 11 2018 1:17pmThen you have the converter you use to rectify the 3phase motor output to a pair of DC output wires, and regulate that charge to your battery.
You could use the existing ebike controller if it has a regen function, but then you will need to run the motor at a speed that generates the right charging voltage to start with (the controller doesn't regulate this). That might change the efficiency you're after.
It also doesn't limit current like a charger does, so if the current flow is higher than your battery can take, you'd want a circuit (even if that's you) that monitors the current and controls the generator speed to keep current within battery limits. Might as well have it monitor voltage too, so it can control speed by that to prevent overvoltage.
YOu could just use a set of diodes as a 3phase rectifier, then take that rough DC and put capacitors on it and run it right to the battery, but again you'll probably want something to monitor current/voltage and control motor speed. You'd need something to disconnect the phase wires from the controller and connect them to the rectifier.
Alternately you can use the motor to generate 115VAC using two phase wires, and use that to run your regular battery charger, as long as it will handle whatever waveform the motor puts out at the frequency it spins at (which will probably be a lot higher than the charger's input was designed for). Keep in mind the motor may spin roughly with a load on only two of the three phases (you'd have to test that). This would also need something to disconnect phase wires from controller and connnect to the charger.
I thought about that also; but I really liked the idea of using a 300g RC gas motor (+2kg of gas) to drive the existing hub motor for recharging.amberwolf wrote: ↑Jan 11 2018 1:17pmYou could use a little RC outrunner instead of the existing DD hub as the generator. Might complicate the voltage/current output conversion, as to get the same power output it'd have to spin a lot faster, so either a lot higher voltage or needs a kV that gets you the same voltage.
It depends on the equipment you have and how it's setup.Buk___ wrote: ↑Jan 11 2018 10:21pmI must admit I thought that a suitable, regen capable controller would take care of rectification and current limiting; and a BMS would prevent overvolting. If that is not the case, it makes me wonder what is to stop regen from wrecking your batteries on a long descent?
Oh, I totally understand, just tossing out the idea.I've no interest in having an RC motor howling whilst I'm riding This was purely a idea for extending range. Find a shop and buy some sarnies, ride somewhere away from people where the noise won't upset anyone, stick the bike on its stand and set the recharge going whilst I eat.
Basically, my controller has a configuration for regen. A single number 1-5 where 1 is high energy recovery/weak breaking; and 5 is low energy recover/high breaking, so my assumption is that if I drive the wheel at an appropriate speed and apply the "EABS brake", the controller will take care of everything else. At least to the point where battery is fully charged, when I just stop.amberwolf wrote: ↑Jan 12 2018 2:14amIt depends on the equipment you have and how it's setup.Buk___ wrote: ↑Jan 11 2018 10:21pmI must admit I thought that a suitable, regen capable controller would take care of rectification and current limiting; and a BMS would prevent overvolting. If that is not the case, it makes me wonder what is to stop regen from wrecking your batteries on a long descent?
If you have "EABS" it is usually a different braking mode than regen.Buk___ wrote: ↑Jan 12 2018 10:46amBasically, my controller has a configuration for regen. A single number 1-5 where 1 is high energy recovery/weak breaking; and 5 is low energy recover/high breaking, so my assumption is that if I drive the wheel at an appropriate speed and apply the "EABS brake", the controller will take care of everything else. At least to the point where battery is fully charged, when I just stop.
The answer to that depends on the specific motor--it's most efficient speed as a *motor* is the same as it's most efficient speed as a generator, for the same voltage and battery current (assuming the same phase current, which it might not be, even with the same controller).The purpose of the OP was to try and find out what would likely constitute "an appropriate speed" to drive the motor for best generation.
I guess I'll have to start a new thread and choose my wording more carefully in order to get an answer to that
Thanks. That is extremely informative. It clarifies much of the fuzziness in my understanding of regen. (I've also taken the liberty of passing it on to here where I think it may also help.amberwolf wrote: ↑Jan 12 2018 1:45pmIf you have "EABS" it is usually a different braking mode than regen.Buk___ wrote: ↑Jan 12 2018 10:46amBasically, my controller has a configuration for regen. A single number 1-5 where 1 is high energy recovery/weak breaking; and 5 is low energy recover/high breaking, so my assumption is that if I drive the wheel at an appropriate speed and apply the "EABS brake", the controller will take care of everything else. At least to the point where battery is fully charged, when I just stop.
Regen itself has at least two ways it works:
--simple way is the faster the motor spins the higher the voltage, but unless the motor is spinning fast enough to get a voltage higher than the battery's present voltage, no current flows and no braking happens.
--complex and more common way is the controller repeatedly "shorts" the motor windings to create pulses of much higher voltage to be able to cause current flow even at motor speeds which would not otherwise be able to do it, so it can brake down to much lower speeds. Some are better at this than others, and some are more efficient at it (the less efficient ones make the motor and controller hotter from the waste heat than the more efficient ones).
EABS is usually not regen, it actually takes power *from* the battery to actively attempt to stop the wheel by applying reverse rotation pulses to it. It's much more powerful braking, and can be done down to zero speed, but it doesnt' get any power back from the wheel (it actually uses it up).
I have EABS on the left wheel of the trike, and regen on the right, and when both are engaged at teh same time for braking, I see a net zero current on the CA with teh controllers I have now. I used to have a regen controller that was very weak regen, and I saw a net negative current, becuase the regen current into the battery was a lot less than the EABS current out of the battery.
I will have to buy a wattmeter -- I was intending to anyway -- but now I will look for a "bidirectional" one also.amberwolf wrote: ↑Jan 12 2018 1:45pmSo if your controller has modes to choose between regen or EABS, or a braking mode where it uses a combination of the techniques (which sounds more likely) in different amounts or in different parts of the speed curve, you'd have to test to see which one works best for your plan. Based on the info so far, I expect the lowest number mode would be the closest to plain regen, and get you the most back, and the highest number mode would get you the least back (or more likely actively use up power).
If you have a bidirectional wattmeter or current meter on the bike (like a Cycle Analyst) you can see whether it's that kind of EABS, or regen, and how much current your system will create at a certain speed and battery voltage. (if you have any kind of motor, even a second bike (ebike or not), you can use it to drive the motor wheel offground at a specific speed to test things with. A second bike you could put on a trainer stand so you can sit on that bike and pedal it if it's not an ebike, and setup your ebike so the motor wheel is friction-driven by the second bike.
Okay. This is where I get confused about regen.amberwolf wrote: ↑Jan 12 2018 1:45pmThe answer to that depends on the specific motor--it's most efficient speed as a *motor* is the same as it's most efficient speed as a generator, for the same voltage and battery current (assuming the same phase current, which it might not be, even with the same controller).
I don't want to say too much because I suspect that my previous comments in this area caused me to suffer a 1 week ban over christmas. Suffice it to say, I don't get on with that simulator.amberwolf wrote: ↑Jan 12 2018 1:45pmI think I already posted it, but if your motor is listed in the http://ebikes.ca/simulator then you can setup a controller and battery similar to yours, and use the simulator to get motor curves, then those same ones would apply as a generator. (given the same conditions)
According to it's specs, that one will require a separate power supply to run the meter itself (it doesnt' run off the power it's measuring). All the cheap ones I've seen don't measure bidirectionally, and/or they don't have their own built in power supply to run off the measured power. There might be some that do both, and they might've been posted around the forum, if you look around for "watt meter" or "wattmeter" posts. (sorry I don't know exactly what else to look for)
The phase wire power is "AC" not DC so a wattmeter won't measure it like you want to. You can measure instantaneous current with a regular ammeter on AC but it also wont' be completley accurate (it's expecting a sinewave, which it won't get, and the current is not constant becuase the phases switch during rotation).And I may buy 2 if I can work out how to insert one into the phase wires. Do you just monitor any pair of the 3 and assume the other two phases to be the same?
Without any controller/charger to limit it, then aside from wire and connection resistance, only the resistance of the cells (Ri) limits it, and that changes with SoC (state of charge). The higher the supplied (open-circuit) voltage vs teh pack voltage, then the higher the current will be, based on that resistance.Okay. This is where I get confused about regen.
When you drive (control) the motor, you essentially supply a voltage, which implies a required speed, and the motor draws as much current as it can until it succeeds in matching that speed (BEMF==inputV), and then the current drops off to just that required to prevent the speed from falling.
When running as a generator (without active interference from a controller), it will produce whatever voltage is commensurate with its current speed, and if that voltage (rectified) is connected to the battery, and if the battery voltage is lower, then a current will flow.
But what current? And what (if anything) limits it?
Yes, depending on the cell resistance.Looking at it another way, if I drive the motor (wheel) at a given speed, and measure the OCV from the rectified output, it should be commensurate with the motor's kV; but as the circuit is open with no load, the effort required to spin the wheel will be negligible. Basically, just enough to overcome friction and cogging forces.
But once I put a load across it and current starts to flow, the force required to maintain the same rpm will increase commensurate with that load.
And (I think answering my own question; but please tell me if I'm wrong ), unless the controller does something to limit the current -- or I do something -- then the battery will draw as much current as the generator is capable of outputting so long as the gas motor can maintain the speed (voltage) above where the battery currently [sic] is.
OK, well, it's the only tool I know of that would show you what you're after. You could try contacting Grin support and see if they can help you out with it, if you're having problems with it. (or just trouble understanding it). I'm terrible at explaining it, so I can't really help with that part.I don't want to say too much because I suspect that my previous comments in this area caused me to suffer a 1 week ban over christmas. Suffice it to say, I don't get on with that simulator.
Thanks AW; much food for thought there.
You can test this to verify, but since the current has to pass thru the meter shunt unchanged to get to the motor and do it's work (or back from the motor to the controller to charge the battery), you can't use the rectifier because it diverts the current and alters it; it doesn't let it do the work it needs to in the form it started as.
Well, the CA does total up the Ah, Wh, A, min volts, etc. and remember these things even when power is lost. It also has a serial output to send the moment-by-moment readings to anything that reads and logs serial data (laptop, arduino, PIC, etc), then you can do whatever you want with that data later.Of course what I really want is a unit that will not only measure, but also log and accumulate. Pretty much what the CA does I suppose; and I might be tempted if I didn't have to shell out again to purchase the logging ability.
It would; might be a bit of work to get it all working glitch-free.At this point I'm more tempted by the idea of connecting a precision shunt to a 16bit ADC and Raspberry PI. That'd give me all the logging I would ever need and the ability to attach different sensors to the ADC for measuring other stuff also.
An oscilloscope could show you the phase waveforms (a 3+ channel would be best so you can monitor all three at once, but a 2-channel lets you monitor two phases which is the same as what most of the phase-current-sensing controllers would do anyway), which would probably be more useful than current measurements, just because you can instantly visually see what's happening. (though I cant' at the moment remember how you'd set it up to always trigger the display sync so you could easily see which way current was flowing, based on the positive / negative voltages shown).The idea of instrumenting the phase wires was to allow me to try and work out exactly what the mysterious C13 setting on my controller is actually doing. Is it just as casainho thinks, just a limit to the number of amps the controller will feed back to the battery; or as I guess -- based on your description above -- also a way of telling the controller to feed some reverse current to the motor to increase the braking affect.
My original (probably woolly) thinking was "work out what speed and power is needed to spin the wheel to generate a 1C charging current" and then find a small RC gas motor, attach a suitably sized mandrel, and fix it to a rotating rack stand with a big spring. Set in motion and eat lunch. Simple
I hadn't considered the complication of the black box that is the controller.
Basically what current limiting does is sense the current via a shunt, and then it begins lowering the voltage as current gets too high, so that the voltage difference between the charger output and the battery are low enough at the resistance the battery is at at that moment, that the current drops to the level the limiter is set at. It increases voltage if the current drops too low, up to whatever the max voltage the system is limited to (so you don't overcharge either).The alternative is that I get a 3-phase rectifier chip, some caps (and maybe a coil?) and some kind of current limiting circuit and bypass the controller; probably feeding the power back to the battery via the charging connection.
But since I know just enough about electronics to be dangerous; have no idea what that "current limiting circuit" would entail; and have never worked with high current DC; I'll save my rainy day notions for another rainy day
I think I may have found my meter.amberwolf wrote: ↑Jan 14 2018 7:51pmRberger just posted this
https://endless-sphere.com/forums/viewt ... =2&t=92367
for raspberry pi logging software for the CA (and the phaserunner but that doesn't apply to your project).
Indeed. I've found a 5v-50v input - 1.2-36V output buck converter for £2.38. There's probably cheaper, but I'm going to build a 48V pack and I'd like to attach a second base unit for that; and over 30V input are rarer.amberwolf wrote: ↑Jan 15 2018 9:36pmThe only issue I see with that one is that it still appears to require a separate 12v external power supply to run the base unit itself, independent from the power it's measuring.
The good news is it's easy to get 12vdc output DC-DC units, with various ranges of input (which would hook up to your battery just like the controller does), to provide that power.
Indeed. I intend to attach the display unit to the same bracket as my current display, so I can take a supply from that.amberwolf wrote: ↑Jan 15 2018 9:36pmThe display unit needs a power supply as well; it says 10-30VDC, so it can probably run off the same 12Vdc as the above. It also seems to say that it will instead run off 5VDC via the USB port, but AFAICT it is saying that's only if you're not using the USB for data (plugging into USB power adapter, like a USB charger).
Given your insight to detecting EABS manually above, I'm no longer thinking about measuring the phase wires. That combined with being able to measure and accumulate regen current at the battery means I should be able to work out what's going on with the C13 setting without looking at the phase wires.
Basically, when there are separate connectors, the LVC only shuts off the discharge. HVC only shuts off the charge.Buk___ wrote: ↑Jan 15 2018 11:25pmThe only complication I see at this point is that my pack uses different set of wires for charging than discharging, which means I will need to break out a plug at both ends of the pack and swap the meter end to end each cycle. I know many BMSs have separate charge/discharge connections, and I think I read somewhere that they offer different forms of protection, but I can't remember where or what they were?
WIth separate C/D connectors, then the regen/charging and running the bike/discharging would only be thru a pack-protected input if you swapped the controller's battery connection between those two each time you wanted to do each one.My pack is in a hardcase and I'd have to take off both ends each time to switch the shunt unit around
It has B- C- and P- only. (If you scroll down this page, it has some hi res images and a connection diagram for my exact model of bms.)
Okay. There are XT60s on both end of the battery (internally) but a round center pin & shield plug for charging (and a rear light and LED meter) at one end; and a 4-blade slide connector (to be replaced by an XT60) and lock/switch at the other end.
That kind of switch probably isn't rare or expensive, but it will be getting on the large side. I have a 3P3T (used as 3PDT-center-off) 30A on SB Cruiser's headlight, and it's something more than 1.5 cubic inches, not including the toggle that sticks out. A 4P would probably be the same in two dimensions, and maybe 2" (or a bit more) in the width.Buk___ wrote: ↑Jan 16 2018 4:59amAs the +ve is common to both ends, I could save switching one wire, but only by sacrificing easy, unplug and go, removal of the shunt/buck module.
I think I would need a quadpole-double or triple throw, 30A capable switch, and I'm guessing without having looked that they are as rare a rocking horse do-do and probably twice the price of a CA3
I did find some 4pole double throw on-off-on switches on amazon US, but they don't ship over here and I found nothing similar on amazon UK. I try AliEx and Ebay Uk next.amberwolf wrote: ↑Jan 16 2018 2:19pmThat kind of switch probably isn't rare or expensiveBuk___ wrote: ↑Jan 16 2018 4:59amAs the +ve is common to both ends, I could save switching one wire, but only by sacrificing easy, unplug and go, removal of the shunt/buck module.
I think I would need a quadpole-double or triple throw, 30A capable switch, and I'm guessing without having looked that they are as rare a rocking horse do-do and probably twice the price of a CA3
That's kind what I was trying to describe a few posts ago. And whilst I have 10 XT60 sets, and I found some alu clamp block to convert them to panel mount; they are bitches to pull apart and I wonder how long they would last constantly being undone/redone.amberwolf wrote: ↑Jan 16 2018 2:19pmAlternately, you could mount the internal battery connectors to a hole in the side of the case so they are exposed to the outside, and build two "blocks" of connectors with jumper wires between different pins, and use one block for charging, the other for discharging. Leave the blocks off entirely for complete disconnection (also makes a decent security key, since without the discharge block in place, the battery is not connected to anything and can't run the bike). I don't know how easy it would be with the connectors you have now, but there are various panel-mount connectors that would make that easy (including some of the Andersons); they may make panel-mount versions of your connectors if you look around.
I found a 4-pole on-off-on switch in the UK at a very low price.
Since you're not switching under load, it wouldn't matter. The DC rating is basically a gap size to ensure that any arc occurring during switching under load gets extinguished. As long as no (significant) current is flowing when you switch, there's no arc.
Yeah, they are big for their current capacity, because all their contact area is on the flat surface, where the XTs it's the whole tubular surface.That's kind what I was trying to describe a few posts ago. And whilst I have 10 XT60 sets, and I found some alu clamp block to convert them to panel mount; they are bitches to pull apart and I wonder how long they would last constantly being undone/redone.
Andersons are great, but damn they are big. And I'd need 8 sets and I've being trying for discrete
You mean basically just doing the job of the switch manually? Yeah, it's simplest to wire, though a bit more complex to do each time.All in all, I think I'm coming around to your earlier suggestion for simply swapping the shunt end to end. It'd mean cutting the plug off the charger and replacing it with an XT60 (NP) and breaking out the XT60 on the charging end of the hardcase bypassing the pin&sheild connector, which is a bit more work.
You're welcome.Thanks a bunch for all your help!
That's a double-pole, so you'd have to gang two of them to siwtch at the same time to get 4 poles, if you really need to switch all teh shunt's wires for your purposes.
It'd probalby work fine for the voltage.Its rated 12VDC @ 20A which definitely wouldn't be enough if it was switched with the current flowing, but if it was only switched after disconnecting from the controller, and before connecting to the charger, and vice versa, would you risk it for 36VDC @25A?
Damn! Musta misread it, or posted the wrong link. This one should work if only switched when no flow.
Cool. I thought that was the case.amberwolf wrote: ↑Jan 17 2018 2:22amIt'd probalby work fine for the voltage.Its rated 12VDC @ 20A which definitely wouldn't be enough if it was switched with the current flowing, but if it was only switched after disconnecting from the controller, and before connecting to the charger, and vice versa, would you risk it for 36VDC @25A?
It'll get warmer than normal when the higher current is flowing, but would probably work fine since you won't be using that much current all the time, just at max load on the motor (which will probably only happen during acceleration from a stop).
Great. Means I can get away with something smaller (&cheaper).
The xt60s in my pack have a sort of clip-on extension on the back. They look pretty flimsy, but actually do make them much easier to pull apart. I found some on AliEx
I didn't realise that. Useful to know if I ever need something that robust.amberwolf wrote: ↑Jan 17 2018 2:08amAndersons have one sometimes big disadvantage: the wire and contact must "float" inside the shell. If they don't (like with really thick wire gauges, or stiff wires bent tightly), the contacts can't self-align correctly, and end up with high contact resistance, which heats them and melts the shells.
Yes, manual; but I haven't given up on an external switch with everything else hidden yet
I was only contracting at KLM for just over a year; I was working as a software engineer specializing in CNC Database software by then. We were setting up a database of CNC designs for small, non-critical parts (seat mounts and similar) that a warehouseman could select and direct to a bank of 4 small 5-axis CNC routers. KLM were trialling it to reduce the amount of stock parts they need to warehouse for their fleet. The in-the-green visit was reward for working a very long weekend -- 60+ hours -- straight through to dig them out of the crap. And very interesting to me as a, by then, ex-mecheng.amberwolf wrote: ↑Jan 17 2018 2:08amBTW, I noticed your post in the other thread about being in the airline industry. I used to do final test/troubleshooting on some of the avionics/displays for Honeywell CFSG back in the late 80s/early 90s, till their layoffs. Once, we had the "funeral procession" as we called it, come thru with a cart full of stuff out of a crashed plane to be analyzed where it was built, in an area near where I worked in the plant. What I learned (second hand) about it got me interested in failure analysis, which I learned more about while still there. SInce then I've followed the various shows about crashes and analysis of what might have caused them, and learned even more. (though I am probably not even a layman in my level of knowledge so far).