Charging pack to 41V experiment

[WheezyRider]

Can you confirm that with your method of reducing the charging voltage (was it NealH who suggested using a diode inline?), the effective reduction in full charge voltage is from 41.7V to 41V? That would giive about 0.7V difference. Saneagle did not give much details how he charged the pack to 41V so it's difficult to interpret his 3% reduction.

No, I don't use diodes inline to control voltage. I either adjust the voltage adjustment pot inside the charger, or as in most cases with chargers recently, change the resistor on the voltage reference IC to give the output I want. I have discussed this in my other posts, most recently:

5A 36V charger, evaluation and modding

If you have a larger pack (15 Ah or bigger), charging at 2A can take quite a long time. On some occasions this this can be far longer than desirable. So if you need to refill your pack a little quicker, what are the options for doing this in a safe way? 3A chargers are available and I have used...

www.pedelecs.co.uk

I have given more details here:

Tuning cheap 42V charger

A while back I bought a couple of cheap 42V chargers as spares, so I could have one at work, at home etc. I got two for just under £10 each. They are quite a lot smaller than the SANS charger and looked good: However, when I checked the output, I was disappointed to see that it was nearly...

www.pedelecs.co.uk

Mikes eBikes 3A charger

I picked up one of these recently and thought I'd give it a once over. It looked quite compact, came with a fan, already had an XT60 connector and I could do with something that charges a bit faster than my SANS chargers. It uses a PSU PCB company that also makes the PSU boards for the Vruzend...

www.pedelecs.co.uk

It is quite easy to do once you have identified the 431 voltage reference IC for controlling the voltage. Some chargers have two 431 ICs, one for monitoring voltage and another for setting the current. So if you see two, you need to check which one does what. Start with very small differences in resistance and monitor the output.

Only do this if you know what you are doing and have the appropriate expertise. Use a calibrated voltmeter to ensure you get the right result.

 

[Woosh]

It is quite easy to do once you have identified the 431 voltage reference IC for controlling the voltage. Some chargers have two 431 ICs, one for monitoring voltage and another for setting the current. So if you see two, you need to check which one does what. Start with very small differences in resistance and monitor the output.

Thank you for publishing your results.
I can order the chargers with 41V output when I am convinced that they are a better choice for those who want longer life and lower risk for their batteries.

 

[WheezyRider]

Sometimes I put a diode inline with the charger circuit on a battery, but this is only to stop a voltage being present at the charger port when the charger is not plugged in. The junction voltage drop of a diode depends on temperature and current level, so it is not an ideal way of accurately controlling voltage level.

 

[StuartsProjects]

I can order the chargers with 41V output when I am convinced that they are a better choice for those who want longer life and lower risk for their batteries.

And which chargers are those ?

I realise you would not sell them seperatly.

 

[WheezyRider]

Thank you for publishing your results.
I can order the chargers with 41V output when I am convinced that they are a better choice for those who want longer life and lower risk for their batteries.

It would be nice to be able to buy 41V chargers without having to modify them. What would be great is a switchable charger, so most of the time you can charge to 41V and then every now and then you could do a charge at say 41.8V to give extra capacity, or to balance. I would not recommend going as high as 42V, keep it to the minimum needed to get the BMS to initiate balancing. Ideally BMS manufacturers should start balance at a slightly lower voltage, eg, 41.6V.

But, you need very good quality control to ensure voltage output is what it says it is. Most manufacturers these days don't care and supply chargers at 42V plus/minus quite a bit. Some are too low to initiate balance, some are too high and damage cells.

 

[WheezyRider]

Grin have been doing it for years:

Satiator - Grin Products - Product Info

The Satiator is a fast and powerful universal battery charger that can be configured to charge a multitude of different battery types and voltages. It allows for partial charging to increase battery cycle life and has an OLED display screen to show realtime charging statistics. This is one of...

ebikes.ca

Ego use packs they call "56 V". Inside they are 14s, so should be giving 58.8. So it looks like they are only charging to 4 V/cell.

BA5600T 10.0Ah BATTERY - Ego Power+

Depending on the product, on a single charge, you can mow up to 1600sqm, line trim up to 280 minutes, hedge trim up to 300 minutes, saw up to 600 cuts or leaf blow up to 400 minutes. The innovative arc shape combats overheating, and maximise run time so you can keep going for longer.

egopowerplus.co.uk

 

[WheezyRider]

I think it's bad of Ego to advertise the Ah of their packs based on the cell manufacturers Ah rating, when that rating is for when the battery is charged to 4.2 V /cell and not 4 V/cell as seems to be the case in Ego devices. So an Ego 10Ah pack could not give 10Ah in reality if they really have used Samsung 2.5 Ah cells in 4p config, charged only to 4 V/cell.

@Woosh, you might want to bear this in mind when advertising pack capacity if you do charge to lower voltages.

 

[Woosh]

At present, I assume that changing to 41V would cause a reduction in capacity around 7% and up to 10% so it's not very desirable in view that the life expectancy of the 42V charging regime is well beyond the recommended 5 years of use.

 

[Woosh]

And which chargers are those ?

I only use SANS charger. I have 2A, 3A and 4A SANS chargers.

 

[WheezyRider]

I only use SANS charger. I have 2A, 3A and 4A SANS chargers.

Do you have a calibrated DVM to measure the output of the chargers? If so, what sort of range of voltages do you get?

 

[Woosh]

I have an ordinary non-calibrated DVM.

 

[WheezyRider]

I have an ordinary non-calibrated DVM.

I recommend you get a decent DVM that is calibrated. Even a 1% error (often good by Chinese DVM standards) in the 200 V range can make a big difference when measuring 42 V, that's a difference of 0.42 V, so you could be way down at 41.58 V or way up at 42.42 V, the difference between not balancing, or overcooking your cells and you'd be none the wiser.

 

[WheezyRider]

I've been looking at DVMs on RS components. Even the calibrated DVMs only seem to have a best DC accuracy of 0.5%. The desktop models seem better at 0.015%

 

[WheezyRider]

Even with a non calibrated DVM, you can still learn something from it, ie what is the charger to charger output variability like? You might not know the exact output, but you can make relative measurements from one charger to the next and see if there is much variability.

 

[WheezyRider]

I've been looking at DVMs on RS components. Even the calibrated DVMs only seem to have a best DC accuracy of 0.5%. The desktop models seem better at 0.015%

Looks like you need to spend around £500 to get anything decent. I'm lucky, I managed to get a couple of Fluke desktop machines that were being thrown out. May be possible to get something on eBay, but it's advisable to re-check the calibration on second hand kit.

 

[saneagle]

At present, I assume that changing to 41V would cause a reduction in capacity around 7% and up to 10% so it's not very desirable in view that the life expectancy of the 42V charging regime is well beyond the recommended 5 years of use.

It doesn't. How many times do I have to explain it to you. it's impossible. Look at these discharge charts. Here's one I just did for you using a brand new Samsung 30q tested on an Opus BT-C3100 tester at 200mA discharge. It was fully charged to 4.2v, then discharged down to 4.09. After some rest, it settled back to 4.10v. It discharged 98mAh during that time. It has a total capacity of around 2750Ah. I can give you that exact figure another time after fully testing.98/2750 = 3.5%. That's the same value as the last test I did for you.



Below is a test by Lygte-info. The result is the same. The lowest discharge rate curve crosses 4.1v at 0.1Ah - exactly the result I got. 0.1/ 2.8 = 3.5%



You guys are nuts. Every theory you make is based on false assumptions and flawed measurement. What you're saying is physically impossible on multiple accounts. It doesn't even pass any basic plausibility test. Entropy always increases.

 

[StuartsProjects]

I've been looking at DVMs on RS components. Even the calibrated DVMs only seem to have a best DC accuracy of 0.5%. The desktop models seem better at 0.015%

A Fluke 87, like what I have got, has a quoted accuracy of;

±(0.05% + 1)

And last time I checked it at one of those Barclays Eagle Labs it was within that. But that was pre pandemic, so maybe time for another vist to their lab again.

 

[WheezyRider]

It's about mass transfer. Electrodes have a fixed surface area. When discharging, ions have to travel through an electrolyte and then percolate into the pores of the electrode. This takes time. You have to wait at least an hour for a battery to reach equilibrium again to get a true idea of what the open circuit cell voltage is.

Also, what was your charge termination current? This can affect the apparent capacity:

Test of Battery Charge Termination Test

He also did a study of Open Circuit Voltage vs. capacity some time ago, where he let the cell rest before taking power out again, but I can't find it now.

 

[Woosh]

You guys are nuts. Every theory you make is based on false assumptions and flawed measurement. What you're saying is physically impossible on multiple accounts. It doesn't even pass any basic plausibility test. Entropy always increases.

I haven 't got a theory. All I want to know is how much my customers would lose in capacity with a charger set to 41V instead of 42V. If it's 3% or less, it's worthwile, if it's 7% or more, I'll pass.

 

[saneagle]

I haven 't got a theory. All I want to know is how much my customers would lose in capacity with a charger set to 41V instead of 42V. If it's 3% or less, it's worthwile, if it's 7% or more, I'll pass.

It's 3.5%, but you gain nothing by doing it . Don't waste your time.