Hotrod up and running... now time to mod!

[lazarus2405]

So, I've finished my first build. It's a 26" faux-Schwinn S-25 full suspension MTB with a 5304 in rear, a modded controller from Bob Mcree (4110 FETs, ~70A limit - I need to measure it, might be lower - and busses reinforced with brass bars), powered by a 84V 6Ah E-Moli pack (21s2p, 15C, LiMn, 6x Milwaukee 28V packs), and a CycleAnalyst plug-in unit. I'll be posting a build thread with pictures after Easter, when I can get back to school. Until then, I will be plotting my next projects.

So, I completed my first mod. I added a toggle to the CA case and wired it to the throttle override. On for legal/sidewalk riding. Off for E-motorbike. I also modded a power strip with Andersons for 84VDC outlets. It happily drives my various electronics' chargers (so far tested things as big as my laptop down to my mp3 player). Another easy mod done. Now it's time for more.

I'll try fechter's low-throttle response mod with a trim pot (as shown here: http://endless-sphere.com/forums/viewtopic.php?f=2&t=764&st=0&sk=t&sd=a&start=56 ) to make things a little easier. That should be a pretty simple one, too. On to real mods.

Charging:

Right now, I charge my batts using three stock Milwaukee chargers. I've left the packs completely intact for charging through their stock BMS (bypassed the BMS for discharging) and simply slide the packs onto the chargers when I get home. I live in university dorms, so I lock my bike in my bike locker and carry my battery bag to my room to charge . It takes ~50min to charge a pack from 90% DoD to full, so I have my full pack of 6 charged in about 2 hours. However, I can't opportunity charge! It's almost as if that alone makes me fail at ebiking.

So, I'd like to shrink down my charging setup to fit in my bag, so that I can leave everything connected and only have to disconnect the controller and plug into an AC outlet to charge. So, each charger has three leads: +28vdc, Gnd, and temp (won't charge if the thermistor is tripped). The BMS does all the thinking, while the charger just is a dc power supply with a red and green light. I'd like to break down the three supplies and make a harness for charging, and store it all in my bag.

So, what problems might I have to overcome? Each charger would be feeding two packs in parallel, while the packs would be connected in 3s2p? Does that circuit diagram out? Will such a setup damage anything? If so, alternatives or workarounds?

Braking and Regen

I need better brakes on the bike, and I have a big honking motor Perhaps there's a connection...

The regenerative braking literature here is really a mess. From what I can tell, I have two options:
fechter's regenerative braking using a cheap brushed controller, as seen here: http://endless-sphere.com/forums/viewtopic.php?f=2&t=583&st=0&sk=t&sd=a

or a non-regenerative resistor coil design, as seen here: http://endless-sphere.com/forums/viewtopic.php?f=2&t=583&st=0&sk=t&sd=a&start=49

Well, I'd much rather do the former, but it's a bit more difficult. In the diagram B and M are battery and motor, respectively?

Looks like I'll take the two bridge rectifier route. The wiring looks clear enough. As for a controller, can you recommend any? Brushless, cheap as possible, able to handle 87V-77V (hot off the charger and LVC respectively), and enough amps? (In retrospect, that sounds like a very difficult request for a brushed controller. What would an alternative be?) As for how many amps is "enough", I can't find the spec pages for my batteries. Perhaps someone out there can help? Since the charger fills 3ah in 1 hour, I'd guess at the very minimum I could pump 6A into them. I don't like the sound of that, though, so a max charging rate spec would be nice. For the throttle, would it be too difficult to use a slide pot and connect it to the bike's brake lever?

Come to think of it, I'd learn more doing both. Simply take a lot of wire to use as a resistor, and a button. Can anyone recommend some good numbers for a 5404? What sort of resistance should I shoot for (as in, in Ohms), and about how much of what wire would this require? ~20' of 18AWG?

More power

Yep, I know. Such is the nature of the hobby, I suppose. I'd like to know what to start thinking about after I expand my battery pack. So, my options as I see them.

I'll get a bit more power from just expanding to 9Ah, since with 6Ah I'm getting a pretty noticeable sag at >50A. Something like 5 to 15V of sag. 50% more capacity should cut that down a bit, right?

After that, I'd want to run more amps. How high can I increase the current limit before things get hairy? 80A? Remember, these are 4110s with reinforced bus bars. I know that the FETs are rated for 180A, and I also know that because it's 3-phase, they'll be able to deliver something in the ballpark of half that. What have some of you been able to run 4110s at?

After that, I'd have to use more voltage to get more power. Since the caps and fets are rated for 100V, and since there's a 10V bootstrap, should I expect failure somewhere between 90V and 100V? Or do they have some headroom? If it was possible, I could easily add another 5 cells (labeled as "18V" packs) for a hot-off-the-charger of 108V and nominal of 104V. Is something like that dancing with death, or doable?

Then, I'd need to upgrade to 150V for more power. What would I have to replace to run at, say, 112V, 140V? Just the FETs and main capacitors? And doing so would generate a lot more heat, somewhere around 5x, I know, but I understand it is manageable. How viable is this route?

So, thanks for any help... I know it's one thread that could easily be three, but I weighed that against polluting the forum, and I'd like to keep it in one conversation. Cheers.

 

[fechter]

Lowell has run 4110s at a bit over 100v input without blowing them up, so apparently there is some headroom. With limiting set at 100 amps on the battery side, you could easily have up to something like 300 amps on the motor phases. The 4110's seem to handle this OK as well.

To go to a higher voltage, yes, just the main caps and FETs you have to worry about if it's an older Crystalyte controller. With other models, you may need to worry about the voltage regulator. The problem with going over 100v is the best FETs available have something like 4 times higher on resistance than the 4110's.

The regen controller thing has never been tested. I'm working on a slightly different version of it that doesn't need a bridge rectifier. If you want to be the guinea pig... you could try it.
The resistor approach is super easy and fairly bullet proof. 20 feet of 18ga. would be a good starting point. A 5304 will need a longer wire than a 5303.

 

[lazarus2405]

Mkay, so exactly what does Lowell run, and how, and on what? Information is sketchy through the search tool. As far as I can tell, he runs a 5303 in a 26" and... a 116V booster pack drawing a lot of amps for his 60mph commutes, with some sort of small aero faring. All on a 4110 controller? How far does he really push it?

I'd love to be the guinea pig for a new design, as long as you can tell me exactly what parts and how to wire it. I'll try the approach with or without the bridge, again, as long as you can tell me what I need. Especially with the brushed controller.

What sort of voltage and current goes through the resistor wire. It seems a shame to use it to just heat my bike frame... perhaps some sort of brake light could be powered off it :lol:

And does my plan for charging wiring work out?

 

[fechter]

I don't have much experience with the Milwaukee chargers, so I don't know if your proposed setup will work. Charging 3 series will be fine as long as the chargers are isolated (I don't know if they are). I have no idea how their BMS works, so don't know if parallel will be a problem.

The "new and improved" regen setup avoids using the bridge by using a brushed controller that has 6 FETs (it's what I had lying around). Something with 3 FETs would work too.

The FETs are normally all in parallel in a brushed controller, so I separated the drains and kept the sources connected to ground. Other than that, it is the same as the bridge rectifier setup. The advantage is there is no bridge, which would not perform well under switching conditions, so the amount of power actually recovered to the batteries would be more. A bridge rectifier would need a large heat sink, which would be eliminated by going direclty to the FETs.

Here's the general layout:

 

[lazarus2405]

Charging 3 series will be fine as long as the chargers are isolated (I don't know if they are).

What does this mean, and how can I determine if they are or not?

So for the braking regen adapter redux, if I understand you correctly, the only bits I would need are a brushed controller, its throttle, and my toolbox?

I'd like to build it, but I can't seem to find a suitable controller on the cheap. To charge 84V of batteries, I would need a brushed controller capable of normally running on a 72V (or so) bike, right? The best I can find (on the cheap) are 48V units. Suggestions?

 

[lazarus2405]

Well, I tried my hand at diagramming my circuit. I'm not a fan of this software so far. What do you use to make your nice neat drawings?



So, how does it look?

 

[fechter]

That looks like it should work.
Chargers that are not isolated have a connection from the ground pin on the AC plug to one of the outputs. If the chargers only have a 2 prong AC plug, then you don't need to worry about it. If they have 3 prong AC plugs, measure from the ground pin to both of the output wires (ohms) and see if there is a low resistance to either of them. If so, there will be a short circuit when you put them in series. If this is the case, you need to break the ground connection on all but one of the chargers.

I use Express PCB's schematic drawing program (free). Google Express PCB and you will find it.

Not sure about a 72v brushed controller. Many 48v units can be modified without too much work, but it would be nice to find one that you don't need to change the FETs in.

 

[lazarus2405]

Nope, they are 2-prong plugs. So I should be opportunity charging in no time. A current limit of something like 100A should be fine with 4110s. I'll try that after I expand my battery. And I'm all set to build the coil resistor brake. All that's left,then, is the regen.

Basically, all I'd have to do is take a cheap brushed controller and upgrade the FETs. Then do some fancy wiring, and I'd have regenerative braking of variable power on a second throttle. No other hardware required; it'd all be done inside the second controller.

So, let's see if I understand this. The brushed controller has a bunch of parallel mosfets used to PWM the battery current into various DC voltages dependent upon the throttle signal and then the PWM gate driver. In normal operation, all the gates are connected in parallel to the driver, all the sources are connected to the battery, and all the drains are connected to the motor. The throttle governs how the MOSFETS modulate the voltage to the motor, thus controlling the motor's speed.

Erm, wait... these controllers do the controlling on the negative side of the circuit... I may have mixed up the sources and drains? Please correct as needed.

In our modification, we're running things backwards. We're disconnecting the drains of three of the FETs from the controller and connecting our motor phase wires to that. The source is connected to ground, which is the controller's battery negative. Then those three FETs are used to rectify the 3-phase AC into high-voltage DC, drawing more or less current based on the PWM signal based on the throttle. Then what? What are the actual batteries connected to? B+ to the controller's M+, and B- to B-? What connects to M-?

Perhaps you could draw a complete new diagram with the FETs connected and showing how everything connects.

 

[fitek]

Sounds like you've got a cool ride going. I'd like to hear how well the Milwaukee packs work out for you. It seems most people are hot on the DeWalts. Also looking forward to seeing how the regen works out, as I don't feel like being the guinea pig

 

[fechter]

I think you got it pretty much right. Inside the brushed controller, the M+ and B+ wires are connected. The FET drains go to the motor, and the sorces are grounded.

The general configuration looks like this: The B+ and B- wires go to the battery. Very little current will go through these, so the wires don't need to be big. The motor (-) buss is chopped into 3 parts and phase wires attached to each part.



When the FETs turn on, they all turn on at the same time because the gates are still tied together. This shorts out the motor windings. When the FETs open, the collapsing magnetic field will circulate current back through the body diodes in the main controller. The freewheel diodes in the braking controller won't be doing anything, so they can be removed. The PWM duty cycle of the braking controller will determine the amount of braking.

When the braking controller is off, all the FETs are open, so there is no drain on the main controller.


Here's my test unit before
View attachment 3

I then cut the motor- buss into 3 segments with a dremel tool:



Then I added wires to each of the 3 segments to bring out to the phases:


Now I just need to extend the wires and put everything back together so I can test it.

 

[lazarus2405]

Replacing the FETs in something like that looks dead easy. I was expecting something with gobs of solder, like on the clyte brushless controllers.

So all that looks pretty good, but I still don't follow just where the current runs back from the wheel to the batteries. You say very little current will run through he battery wires. I'd expect, then, that some 30amps of braking current would run somewhere else.

When the FETs open, the collapsing magnetic field will circulate current back through the body diodes in the main controller.

Is this the relevant bit? When the FETs short the motor, the current will run through the phase wires into the primary controller? And this will be high enough voltage to charge a pack that's ~3x the motor's back EMF?

And, the next question, will CA be able to read that as regen current if the regen current is flowing to the batteries through the main controller?

 

[fechter]

I think you got it. When the regen controller shorts out the windings, current flows through it. When the PWM opens the switches, there's nowhere for the voltage to go execpt through the body diodes in the main controller, back into the batteries. If the CA is in series with the batteries, it will read the regen current. Even at very low speeds, you will get regen back into the batteries. The regen current will be passing from the motor back through the main controller (even though it's off).

 

[lazarus2405]

Well, let me know how your testing goes. If it works out, I'll see if I can get the parts, and I will start a build thread for it.

About how many amps will the regen controller need to be able to handle? And will its current limit still be able to be used to keep the batteries from being charged at too high a rate?

 

[fechter]

That's a good question.
My brushed controller has a current limiting circuit that works by measuring the voltage drop across the FET (no shunt). I'm hoping that the limiter circuit will still work otherwise I might have to make a separate limiter just for regen. I'm thinking I want to limit the regen to 20 or 30 amps. In my case, the limiting factor is probably the drive belt. If it goes too high, the teeth will start skipping over the cog.

With no limiter, you would be able to practically lock the motor if you turned the regen up to 100%. This could break something mechanical. The current in the braking FETs could exceed their rating. I'm also planning to limit the duty cycle (throttle) on the regen. This can be done by adding a trimmer pot, making the upper limit adjustable. This might take the place of limiting if you set the max low enough. An actual limiter would be better.

It would be a good idea if there was a high voltage cutout that throttled back the regen if the battery voltage exceeds a preset value. I doubt this would kick in very often, but if you were fully charged at the top of a hill, you would not be able to absorb the charge and would have to rely on friction brakes. If you also added a large wire resistor, you could dump excess charge in the event the batteries are full. This would take yet another circuit.

 

[lazarus2405]

It would be a good idea if there was a high voltage cutout that throttled back the regen if the battery voltage exceeds a preset value. I doubt this would kick in very often, but if you were fully charged at the top of a hill, you would not be able to absorb the charge and would have to rely on friction brakes. If you also added a large wire resistor, you could dump excess charge in the event the batteries are full. This would take yet another circuit.

You have an interesting mindset. For you, a circuit to do something you can do yourself is easier. For someone inexperienced in circuit-building, I'd rather be mindful of my battery voltage and use the wire resistor brake we discussed in such a situation, than build another circuit to do it for me. For someone with more experience with the matter, constructing yet another circuit seems to be the easier route. Just an interesting point of view. Perhaps later, I'll be so inclined.

Any testing of the regen controller yet? Let me know how it goes. Also, is there any chance you (or really anyone on these boards) could sell me one suitable for the project? Looks like I could replace the FETs no problem, but I can't seem to find a used junky unit to start with.

 

[lazarus2405]

How about one of these: http://www.evparts.com/prod-CT5310.htm

I can't find any disassembly pictures of it, but it looks like it might do.

Please keep me updated of any tests. :-D

 

[fechter]

Not sure what's inside one of those. One of the YK-?? things from TNC scooters might work too. There are pics of the guts around here somewhre.

Actually, we should move this disscussion over to:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=583

 

[lazarus2405]

Mkay, I'm posting a summary of what's been discussed here re: regenerative braking over on that thread. Further discussion there.