How can I partially discharge Bosch battery?

[webcurl]

Perfect, thanks for advise.
I have connected directly 220V 100W bulb to battery terminals and supplied +5vdc to "charger" terminal and BMS is not tripping anymore.
But I need to increase load as my 1 bulb 220V 100W takes ~0.18A only (measured by multimeter) and it will take forever to discharge the battery.
Resistance of bulb + wires ~36Ohms + battery resistance ~98Ohms gives 134Ohms
I=U/R; I=36v/134Ohm=0.26A which is close to multimeter readings.

Thanks again for yours advice.

Out of curiosity, what was the resistance of the 3 x 12v globes?
FYI, on the German pedelec forums, people mentioned their Bosch battery charge cycle count was getting incremented rapidly by playing around with the 5VDC on the CAN line, how accurate this is, i have no idea.

 

[webcurl]

We were fortunate that we knew last fall when our last ride would be, so we didn't charge after it. Saying that, I wonder how many folks actually worry about charge level for seasonal storage? I also wonder if the risk of damage in rigging up a discharge solution is exceeds the (theoretical) gain from partial discharge before storage?

I just go for a short ride, taking 2-5% off the top has got to be better than leaving it at 100%.

 

[Nomad]

that wont work with a mid drive without a throttle. the headlight and computer will turn off after a few minutes of inactivity

If he mean run the motor as in pedal it it would or you could just pull a Danny and just ride up and down your stairs in your house

 

[Alex Baybak]

Out of curiosity, what was the resistance of the 3 x 12v globes?
FYI, on the German pedelec forums, people mentioned their Bosch battery charge cycle count was getting incremented rapidly by playing around with the 5VDC on the CAN line, how accurate this is, i have no idea.

The resistance was 1.8 Ohms only...
Thanks for info. Currently I have connected 5.04vdc from an old cellphone micro USB charger.

As per now I have connected two 220V bulbs, in parallels, they are probably 100W each (not sure because no label anymore, that's only the incandescent bulbs that I have found at my house)
The battery is discharging with 0.48A on multimeter, so I need to add at least two more bulbs to reach ~1A.
So the experiment is confirmed to be working. Need to make it on a rail and to buy more E27 sockets.

That is my battery discharger prototype:

The white bulb filament is not visible, but another bulb is lightning with very low brightness.

 

[Alex Baybak]

Why not use several bulbs in parallel and add a timer? It may take several hours to get the voltage down to storage level. Is there a reason you need to discharge the battery quickly?



View attachment 114290 View attachment 114291

With 6 bulbs, the total draw is 2A which sometimes takes a few hours to get the charge level I want. More bulbs could be added if necessary but I have no need for a faster discharge rate. Simple math tells me how long to activate the timer so I can set and forget it. I have the bulbs mounted on a wood strip which hangs on a wall for use as a portable light source during our frequent power outages.

For convenience, I added this voltmeter to easily check the charge level:

Amazon.com

Yep, now I know and I like to fabricate something like yours rig.
2A for discharge is perfect I think, no need more.
As for now I get 0.48A only, but will add more bulbs in parallel.

I also wonder if the risk of damage in rigging up a discharge solution is exceeds the (theoretical) gain from partial discharge before storage?

Nice question BTW. The risk is persisting for sure.

 

[retiredNH]

I think an easier approach would be (and this is what we essentially did last year) was charge before you ride as you lead up to the end of the season. I doubt that many folks do long rides impromptu where they wouldn't have time to charge first.

 

[webcurl]

Just as the Bosch BMS senses & stores information: cycle count, hi/lo Temp., voltage, power in/out (gas gauge), etc. I would have thought that for the new smart system they would make it even smarter with:
Capacitor based cell balancing.
Thin strips around the cells that could warm the battery in extreme cold conditions & slowly discharge the battery when 100% charged and storing for too long.
Via 2 user options:
1) Allow battery to warm itself in cold conditions - On/Off, option to specify low temp xx degrees.
2) Automatically discharge battery after sitting idle for too long - On/Off, amount xx% to discharge & after xx days of sitting idle.

Entirely possible.

 

[6zfshdb]

I also wonder if the risk of damage in rigging up a discharge solution is exceeds the (theoretical) gain from partial discharge before storage?

This is a very good point. Unless you know what you're doing, playing around with these large capacity lithium batteries can indeed be hazardous. For those who aren't DIY inclined, it may be best to risk battery damage from storing at a high SOC rather than from fooling with the circuitry.

 

[PedalUma]

Rent the bike to some high school kid for an hour. Make $5 and drain the battery.

 

[PedalUma]

The other way is to immerse in seawater. This way is fastest. Li loves water.

 

[fooferdoggie]

The other way is to immerse in seawater. This way is fastest. Li loves water.

primitive pin it with a nail from a pneumatic nail gun.

 

[Stefan Mikes]

Just as the Bosch BMS senses & stores information: cycle count, hi/lo Temp., voltage, power in/out (gas gauge), etc. I would have thought that for the new smart system they would make it even smarter with:
Capacitor based cell balancing.
Thin strips around the cells that could warm the battery in extreme cold conditions & slowly discharge the battery when 100% charged and storing for too long.
Via 2 user options:
1) Allow battery to warm itself in cold conditions - On/Off, option to specify low temp xx degrees.
2) Automatically discharge battery after sitting idle for too long - On/Off, amount xx% to discharge & after xx days of sitting idle.

Entirely possible.

You're worrying for battery heating up in Australia? Li-Ion batteries hate overheating far more than overcooling. People typically bring their charged batteries from home, that is, warm. When you're riding, the battery heats up itself because of the internal resistance. In cases of extreme frost, the battery can be wrapped in a Fahrer-Berlin neoprene cover.

I ride during Polish winters. I carry a spare battery in a pannier and swap batteries after some 2 hours 30 minutes of the ride. I can monitor both the battery and motor temperature. It has never happened the internal battery temperature dropped below 0 C! Even at -14 C outside!

I think it is better to ride more than spend time on unproductive reasoning what Bosch or another manufacturer could do better. They know their trade.

P.S. It is 6:50 am and 0 C outside here. I'm going for a ride.

 

[webcurl]

You're worrying for battery heating up in Australia? Li-Ion batteries hate overheating far more than overcooling. People typically bring their charged batteries from home, that is, warm. When you're riding, the battery heats up itself because of the internal resistance. In cases of extreme frost, the battery can be wrapped in a Fahrer-Berlin neoprene cover.

I ride during Polish winters. I carry a spare battery in a pannier and swap batteries after some 2 hours 30 minutes of the ride. I can monitor both the battery and motor temperature. It has never happened the internal battery temperature dropped below 0 C! Even at -14 C outside!

I think it is better to ride more than spend time on unproductive reasoning what Bosch or another manufacturer could do better. They know their trade.

P.S. It is 6:50 am and 0 C outside here. I'm going for a ride.

I'm not worrying about mine overheating, i have an R&M and it comes with more to begin with, no need to call them range extenders either
It'll be a cool 19 C at 6am here.

I was thinking about people like yourself where you are in that if your battery get's too cold in the pannier or forget to 'care' for the battery before you use it.
It wouldn't take a huge amount of power to "take the edge off" the cold.
I'm an ideas person, i enjoy thinking up ways how things can be improved.
I think you lose a bit of Ah when it's too cold? And i think it's the chemical reaction that warms them up when being used.
Bosch may know their trade, and in many areas they certainly do but in my mind they are a bit slow to progress.
At least i think the foolproof self discharge if sitting around too long idea is a good one, that will happen.
Capacitive cell balancing has been around for a while (years) and makes for more efficient battery capacity with not much more cost.
The micro thin "heating element" strips would form a dual purpose - keep warm when cold (if enabled) & slowly discharge to a certain level if forgotten about when fully charged.

 

[Stefan Mikes]

I was thinking about people like yourself where you are in that if your battery get's too cold in the pannier or forget to 'care' for the battery before you use it.
It wouldn't take a huge amount of power to "take the edge off" the cold.

Some stats for you, based on real life:

Ambient temperature for the ride.

The e-bike was one hour and seven minutes outside.

Battery temperature:
- Min: 9°C (it was when the bike was waiting for me outside the store for 23 minutes, power off)
- Max: 21°C (the initial battery temperature)
- ∅ : 13°C
Battery temperature measurement.

Motor temperature:
- Min: 6°C (the motor got even colder than the battery while outside the store!)
- Max: 38°C (Turbo mode ride, SL 240 W motor)
- ∅ : 26°C
Motor temperature measurement.

If you think it was not any representation of winter riding, I can remember my "Polish Blizzard Ride" on Vado 5.0 very well.

127% means I had to swap batteries on the ride.

Ride metrics...

Winter? I do think so.

It only started snowing when I took that video.


The bottom line:
Why should the industry invent something absolutely unnecessary? I even do not use neoprene battery covers on my e-bikes!

 

[Alex Baybak]

Continuing my challenge as per discharging Bosch Powerpack & Powertube 500Wh batteries.

1. I have connected two 36V 40W incandescent bulbs in series. Such a way I get enough resistance to make BMS not tripping. In such configurations I can suck only ~850-950mA from the battery.
So the discharge from 40V to 30V takes ~14-15 hours, still testing and logging in progress.
I have tried to connect more powerful bulbs in parallel but once the current reaches more then 1A the BMS trips. Already tried different discharge circuit configurations, but result-less. Once current reaches 1+A BMS trips.

2. After discharge to 30V I have charged the battery back by compact Bosch charger 2A until the full charge.
Once the charge is completed I have witnessed that the Battery status LEDs (5 pcs) are powering off, meaning that BMS disconnecting main battery terminals from the charging port while the charger is still plugged. And this is an another issue.
Why, because once I try to discharge back the fully charged battery by connecting my discharging rig - the BMS after 30 seconds of discharge is disconnecting the battery terminals from charging port and is not letting me to discharge the battery. Probably a kind of overcharge protection, and as I use a charging algorithm (suppling 5VDC) to make it discharge, but BMS thinks that somebody is trying to charge more already fully charged battery instead and cuts off the main battery... That is my understanding of the process. So many protections.....

Afterwards I have installed the battery on the bike and made a ride for ~1km to slightly discharge the battery. Only after this, once I have placed the battery back to my workshop and connected my discharge rig - I have been able to discharge it without any BMS tripping.

So the above-mentioned discharging rig is working only when the battery is charged not more then 85-90%

That is it for the moment. Any suggestions are very welcomed.

 

[john peck]

Put yur tongue in the connection til yur muscle spasms stop. (kids, don´t try rhis at home)

 

[webcurl]

I have tried to connect more powerful bulbs in parallel but once the current reaches more then 1A the BMS trips. Already tried different discharge circuit configurations, but result-less. Once current reaches 1+A BMS trips.

You do know 2 x 36VDC Batteries in Parallel effectively = 36VDC but 2 x 36 Ohm resistors in parallel = only 18 Ohms?

Series and parallel circuits - Wikipedia

en.wikipedia.org

 

[fooferdoggie]

the easy way is to pay a kid to ride the bike around in your basement or on a trainer.

 

[rich c]

We were fortunate that we knew last fall when our last ride would be, so we didn't charge after it. Saying that, I wonder how many folks actually worry about charge level for seasonal storage? I also wonder if the risk of damage in rigging up a discharge solution is exceeds the (theoretical) gain from partial discharge before storage?

No such thing as a last ride here. I ride year round as long as there is something cleared off. I won't ride on ice.

 

[Alex Baybak]

You do know 2 x 36VDC Batteries in Parallel effectively = 36VDC but 2 x 36 Ohm resistors in parallel = only 18 Ohms?

Series and parallel circuits - Wikipedia

en.wikipedia.org

Sure, I know. You are meaning that the resistance is low in parallel 36V bulbs connection. And it's correct. But BMS trips not only because low resistance but also due to current more then 1A. I can explain.
I have connected two 36V bulbs in series (I got enough resistance to make BMS not tripping) and additionally in parallel I have connected one 220V 60W bulb to get slightly more amps. Ok, when I connect to Bosch battery and it's voltage let's say is 36V the discharge current is 920mA and not tripping. But if the battery initially is more fully charged, let's say 39~40V once I connect the same as above discharge load the current is already ~1080mA and BMS is tripping. In both cases the resistance is the same, right? But in spite of this BMS is tripping, that's why I have made a decision that there is not only low resistance protection but the amps as well. Correct me if I'm wrong.

I know that it's not required to majority of ebike users, but I have a desire to sort this out. And advises like where to put the tongue are very smart indeed.