Ping batteries and regenerative charging

[greglocke]

Hiya all

Has anyone had any experience with running the new version 2.5 ping batteries with regenerative? Pings notes say to add a reverse current blocking diode in line with the power wires, and connect these wires together with the charging wires so any regen currents gets sent via the BMS. I would have thought there was no chance of overcharging the batteries or them needing balancing when doing regenerative braking. My ping is a 48 volt 15Ah and it states max charge current of 5A, but I see other 15Ah pings.. both 24 and 48 volt having 8A max.. and the lifetime specs say recharging current less than 1C (15A). Braking from 50kph (nine continents 2806 hub motor) would maybe throw out 10A, but only for a second or so.

I am loathe to add in a diode as the total power loss over time from this would be as much as regenerative adds (I have a long brakeless commute in the country, but some town stuff too where reducing the load on my brake pads would be beneficial)

anyone got any experience or views on this?
this is pings notes here with a picture. The regen notes are on page 6.
http://www.pingbattery.com/usrguide/Wiring%20Guide%20V2.5.pdf

cheeers! Greg
New Zealand
Ping 48v 15Ah, Nine Continents 2806 in 700c wheel. 25A controller.

 

[thewmatusmoloki]

Gday Greg,
I ran regen braking on my golden motor setup (48/20 ping v2.5) with a 20amp controller, without a diode or any problems, for about a year. (before upgrading)
I didn't have any way to measure the regen amps, but it couldn't have been much. You might want to be careful with a more powerful controller though.

One thing I want to say about regen is, If you've had it, you get used to it.
When it was gone I kept gently squeezing the brake lever and was surprised when nothing happened :lol:

To me it was a bit like ABS on a car. If I was traveling at speed down a hill in the wet, I knew I could slow down safely without the wheel locking up (takes a little time for your braking habits to change though)

I just recently got regen back through upgrading to a programmable controller (for the headway, still no diode)... I love it, not for any returned power (negligable), just for the "electric" braking.

 

[Kiwi]

Hi,

I have been using Ping batts with regen. No issues so far, and have not included a diode.
However, seeing this post and info creates concern that I should be.

What are we gaining by running it through the BMS?

 

[greglocke]

yeah, thanks guys. My thoughts too. I would think given the wee amount of time that the current is exceding 5A is real small and even then the battery looks like it should cope with 10A anyway fine. Other LiFePos quote more charging rates of 3C possible. Is there something different about Pings? My gut feeling is it is just maybe a precaution in case cruising down the himalayas or something. But I'm still into getting a bit more opinion or experience before just letting the controller dump straight into the battery. That writing in red by Ping looks quite ominous.

I just check nine continents site and they have the graph below...
http://www.ebikes.ca/store/images/Regen_Amps_2010.jpg

im running 48 volt, and my 700c wheel with 622 x 40 tyres means at 50kph it is doing 380 revs. So that's 8A max for a couple of seconds.

I'm heading towards just doing it.

 

[dogman dan]

That diagram makes a lot of sense to me. I have to wonder if any of that regen power even makes it into the battery if it is not done that way.

 

[thewmatusmoloki]

Greg, I would be careful about this, your 700c wheel + 25amp controller means that a whole lot of regen force is there quite suddenly, back through the bms.
If it was me I'd just do it and see what happens, but I've always been the "guinnea pig " type.

You might want to reconsider getting the diode option , perhaps.
There may be no current alternative solution at this stage , it seems.

 

[greglocke]

Hmm.. yes. I am thinking I don't know enough about the internals of the BMS to assume it should be OK without a diode so I think I will indeed follow Pings diagram. If I could just plug it in without the diode and see what happened then it would be interesting, but if it isn't charging right I probably won't know, and it would probably mean just the battery lifespan is reduced, and again, how would I know that has happened without a parrallel universe where the same me is running a correctly modified system??

oh for a parrallel universe for ebike science projects 8)

 

[HTB_Terry]

The main problem with using regen on a lithium pack without additional protection is that the BMS will not protect the cells from over-voltage. You might be thinking that the BMS has OV protection so the cells will be safe...NO! What do you think happens when the BMS detects an OV condition? It turns off the *charger* mosfet, not the discharge mosfets. So when you are zooming down the hill generating 60V+ into a 36V pack, you will cook the cells, because you are pumping current into the output, which is not turned off in an OV condition. The purpose of Ping's circuit is to re-direct the regen current into the charger input which is protected by the BMS. You can also use a relay to switch the controller from the discharge path to the charger input if you don't want the power loss from the diode. Using the BMS to protect the cells from regen is dicey at best. An external voltage and current regulator circuit would be alot safer. Some regen controllers are supposed to regulate these but I doubt they are accurate.

 

[Kiwi]

I emailed ping.

This from him.

Thanks for your information.

I cannot open the web link now. Internet connection to the US sometimes is not so good.

Please help me explain to them about the BMS and regen controller.

I think they should have the diagram of the diode for regen controllers in our guide. Attach it here anyway.

The reason why we add the diode is that there’s no over-charge protection on the discharge wires, while regen power is usually going through the discharge wires. So, if a battery pack is right fully charged, and you ride the bike downhill for a period of time, the regen power will over-charge some cells. However, the diode can direct the regen power to the charge wires.

Regarding the 5amps maximum regen current, it’s based on the condition that you put the diode in the circuit and it’s actually limited by the charging MOSFET on the BMS. If charging current is higher than 5amps, the charging MOSFET will be very hot. But it can still withstand less than 10amps charging current for a short period of time.

So, you can see that the diode is not a must if you understand why we add it.

If you turn off the regen function when the battery pack is fully charged. Then when 10% or 20% power is used or there’s no long downhill way in front of you, you can turn on the regen function. If there’s a switch for regen function on the handle bar, it will be very easy to do that.

Why we didn’t put it in the guide is that we want to be conservative. Because not every customer would like to read all the words. Do you think we should explain it in the guide?

Best regards,

Ping

 

[greglocke]

Thanks for doing that Kiwi.. that explains everything, looks like it would be fine for me to just connect without the diode now. I live in a fairly flat place so it is only usual braking for traffic lights and corners that takes place. I may disconnect the cutout wire from the front brake handle so when fully charged I just use the front brakes for a bit (while letting go of the throttle manually which I do anyway). Then after a few ks use the rear brake as well which has the cutout and thus will enable to regenerative braking.

Excellent!. I'd though of a relay as well but it was all getting to be too many wires and things to go wrong. I like this simple answer the best. Time to get out the screwdrivers and enable the regen!

Greg

 

[thewmatusmoloki]

Yeah, thanks Terry & Kiwi for turning this thread into something that we can all learn from.
Nice.

 

[yopappamon]

Very interesting regen discussion. I was considering disabling my regen, but I thought I would get some data first.

I turned on my cell logs for the ride home from work. 6.5 miles, I start out going through a parking lot, a short stretch of sidewalk, then an approach to the Metro train station, walk across the train platform, then down the wheelchair ramp to go under the tracks. The ramp is a couple hundred feet long, goes down 12-15 feet in elevation. This is the first place that the regen will kick in for any length of time.

Full ride graph


I've labeled the graph A to F for what happening as follows:
A -Walking across the full length of the train platform
B - riding down the ramp, regen on full, no regular brakes until the bottom
C - riding under the tracks
D - riding up first half of ramp up
E - turning around to go up send half of ramp
F - second half of ramp up

I kept the batteries on the charger and bms all day, then disconnected after I started the cell logs. 36v pack 20ah, LiFePo4 thundersky's. 9c rear hub.

First highlighted area


I can see I do have one weak cell. I was wondering how high the voltage would spike on regen, but it looks like it's not that bad if you aren't going down a long hill.

 

[greglocke]

looks good, cool. I see the right hand axis is the individual cell voltage, but what is the left hand one?
I still haven't had a test yet of my setup with the regen activated yet, (NZ wet winter time) but will post a results update when done.
Greg

 

[yopappamon]

The right axis is individual cell voltage.

 

[greglocke]

Hiya all. I just thought I'd give a bit of a follow up to the regen on the ping battery. I activated the regen on the 25A infineon controller that came with the nine continents kit and just left the controller wired direct to the power output of the battery. i.e. no diode, and no connection to the BMS wires. So the power from the controller is being dumped directly into the battery with no management or safety other than that provided by the controller.

Well all seems to be good. Using regen braking from 50kph starts off dumping around 9 amps into the battery (my battery is 48volt, 15Ah ping) The braking effect is really quite light (total weight of bike and me is 125kg,(275 lb), 10 x 6 nine cont in 700c wheel) taking around 30 seconds to come to a stop from 50kph using regen alone. The retardation is quicker to start with.. (more natural drag, as well as higher power being generated) but there would still be 7 or 8 seconds when the regen current is greater than 5amps. So I think if I had done as in the manual and wired via the BMS I may have indeed damaged it from braking at these speeds. The output from this controller at these speeds is just a bit too high.

The only thing seems to be to don't regen brake down a steep hill straight after charging the battery. Really.. so long as the first ride is on the flat it will always have used up more power than it can try to put back into the battery when braking afterwards.. else we would have a perpetual motion machine and could all get incredibly rich!

Cycling round town seems to be giving an extra 6% or so in range according to the cycle analyst.. which is certainly worthwhile.

thanks again all, if I come across any problems or new info I will post details.
Greg

 

[auraslip]

I'm glad I just found this!
The diode ping sent me with my battery seems to have died.
On the controller side of the diode it reads 29 volts. On the battery side the pack reads 59 volts. The diode looks very poorly made. Big blobs of cold solder.
I'm going to take it off. Maybe I'll get some speed boost from not having it!
Anyone have an idea of the resistance and power loss of having a diode?

 

[Rifle]

Also very glad to have found this. Surprised there wasn't an "expert" answer to this question, though it does seem we have a pretty good answer to the question now. Being that the only one we know to wire it properly ended up almost melting his charging MOSFET, I'll probably have the front brake be normal and the back one be for ebraking too. Still wish there was a better solution. With all the extra weight on the bike I think down some long steep hills I get going significantly faster than 30mph (50kmh) and wonder if it might get up to unacceptable ranges for the current. Probably shouldn't allow myself to get going that fast in the first place . Maybe I'll also add a switch on the handle bar to the one ebrake so I can turn it off on occasion.

 

[Kiwi]

I get 7-8amps going back in to my 72v pack slowing from 60km/h to about 40.

Before I had regen and disks, my rims got so hot one day on a down hill that I melted the inner tube and got a flat.

 

[el_walto]

The 48V Ebikes.ca infinion controllers will Cut out Regen at 57 Volts so it is safe to connect them directly to the discharge wires if your pack is somewhat in balance.

 

[auraslip]

My bike seems a little faster with out the diode.

Also the BMS mosfets barley get warm now. Before they got hot enough to melt the solder holding them to the board.

 

[dnmun]

ping is trying to prevent you from overcharging the pack. the BMS will block the flow of current if one of the cells climbs above 3.9V.

if you can keep regen turned off when the pack is fully charged, that risk is reduced when the regen currents are still relatively low.

the diode is just like a light bulb and will always be hot if current is flowing through it.