5A 36V charger, evaluation and modding

[WheezyRider]

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 one for some time, but I wanted something around 5A, so I can recharge in just a few hours. For a 15 Ah pack, with 6p banks this is still less than 1 A per cell and this is less than the charging rate of many USB banks.

Before charging any battery with an eBay charger or one from similar sites, it's always advisable to check it inside and out to make sure it is safe and fit for purpose. I do not recommend doing this is you do not know what you are doing. This information is provided for general interest, but it should only be acted upon by forum members with suitable expertise. Charging batteries is dangerous. Opening mains appliances is dangerous. Modifying will invalidate warranty and if you do it wrong you could burn your house down etc, etc...you get the idea.

I found this one on eBay and it looked interesting:



It came with some basic info:



So the spec for the voltage was 42 +/- 0.3 V. When measured, the output voltage was 42.1 V and the current was 4.7 A. It weighed in at 355 g. The cable retainer on the output was quite a sloppy fit for the case and it rattled around a bit. So to the insides...





It was held together with a couple of anti tamper screws, but a suitably sized flat balded screw driver got them out. It came apart quite easily after that...



Soldering was not too bad, no dry joints and not too much spatter, although there were a few blobs that could come loose in use:





I wasn't happy with the output being over 42V and as I only charge my packs to 41V I wanted to modify the output of the unit. In this case, the 431 IC voltage reference that controls the output voltage was a TO92 rather than a surface mount:



Then it was a case of finding the voltage divider chain. This had me stumped for a while, as I assumed blue would mean negative and brown positive, but I eventually read the text on the board and found this wasn't the case! There was also a big blocking diode between the output and ground. But eventually I traced it out.






I desoldered the 11k resistor and added a 300 Ohm resistor to the chain. The voltage increased to 42.493 V. So after a bit of trial and error, I replaced the 11k resistor with a 10k and a 100 Ohm to give 41.087 V. I left it at that because I've often found that if you are using a Watt meter, the shunt inside it drops the voltage by about 50 mV.

I wasn't happy with the output cable, it was too thin for my liking, considering it will be taking 5A. I found some thicker cable, with nice red and black coloured wires. I bored the holes in the PCB slightly larger to take the thicker wire. I put an XT60 connector on the end. I also had a spare cable retainer knocking about from another project that was a nice snug fit for the case and this was attached to the cable with some superglue:

 

[WheezyRider]

So then I re-assembled the case and put the screws back in:




I connected it to the pack and it charged fine. The charger got warm to the touch, but not as hot as my old 2A SANS charger. The green light came on when the current reached approx 240 mA, but the voltage was still not at 41V. It did eventually drop down to a negligible amount. During charge it was satisfying to see the Watt hours going in so quickly, a few miles range added in a matter of minutes.

 

[StuartsProjects]

I do like chargers with a fan .............

 

[cyclebuddy]

The question should be whether your BMS can take 5A. Two of my batteries for one of my e-bikes the manufacturer says can take a maximum of 4A, but they don't recommend it nor do they make/supply a 4A charger.

I do like chargers with a fan .............

I don't. Power supplies designed with a fan use small heatsinks because the design relies on that fan to cool. Fan is most often very cheap/noisy with poor bearings and most likely to fail long before the other components do. Failed fan = rapid overheat and instant failure. PS's without fans have decently sized heatsinks to dissipate that heat naturally, although some kind of venting usually helps convection cooling rather than a sealed enclosure.

 

[WheezyRider]

The question should be whether your BMS can take 5A. Two of my batteries for one of my e-bikes the manufacturer says can take a maximum of 4A, but they don't recommend it nor do they make/supply a 4A charger.

I don't. Power supplies designed with a fan use small heatsinks because the design relies on that fan to cool. Fan is most often very cheap/noisy with poor bearings and most likely to fail long before the other components do. Failed fan = rapid overheat and instant failure. PS's without fans have decently sized heatsinks to dissipate that heat naturally, although some kind of venting usually helps convection cooling rather than a sealed enclosure.

What size is the battery pack? It sounds like it must be a small one if the BMS can only handle 4 A charging? The BMS I have on my packs are all 25 A charging, 50A discharging and my smallest pack is 15 Ah. As I said, 5A charging is for bigger packs. One of my packs is a 15.6Ah Silverfish. It is a borderline case as the charging circuit contains a 5 A fuse. This is probably just about ok if the charger is outputting 4.7A, but I'd rather not risk it. I intend to use this 5A charger on packs I have built myself, or ones where I have replaced the BMS.

 

[cyclebuddy]

My packs are 11Ah, but they make larger ones too and don't recommend above 4Ah (My guess because charge connectors, wiring etc over sustained charge times will heat/melt in extreme cases). A 5A fuse typically takes 10A to blow. It'll sustain 7/8A for quite a long time.

 

[WheezyRider]

My packs are 11Ah, but they make larger ones too and don't recommend above 4Ah (My guess because charge connectors, wiring etc over sustained charge times will heat/melt in extreme cases). A 5A fuse typically takes 10A to blow. It'll sustain 7/8A for quite a long time.

Yes, it's a bit small, 4 A sounds about right. Plus if you have 5.5 mm barrel type connectors, they are not usually rated for more than about 3 A.

There is a 20A fuse in the output of the Silverfish, but I frequently draw up to about 28 A from it and it doesn't blow. Seems to need more than 30A for it to go.

 

[Woosh]

a fast charger is an attractive proposition but should we warn potential takers that fast charging accelerates the ageing of your battery?

 

[WheezyRider]

a fast charger is an attractive proposition but should we warn potential takers that fast charging accelerates the ageing of your battery?

True, but as I said, with a large battery (15Ah min), the current per cell is still quite modest. For a 6p pack, it's still less than 1 Amp per cell, which is less than the charge current of many USB banks and the typical 1 A used by https://lygte-info.dk in his tests.

 

[WheezyRider]

True, but as I said, with a large battery (15Ah min), the current per cell is still quite modest. For a 6p pack, it's still less than 1 Amp per cell, which is less than the charge current of many USB banks and the typical 1 A used by https://lygte-info.dk in his tests.

The other thing is you wouldn't need to use the 5 A charger for every charge. If you are not in a hurry you can always go back to using a 2 A charger. It's mainly on those days when you know you are going to need a quick turn around that it is very useful to have.

 

[guerney]

If you have a larger pack (15 Ah or bigger), charging at 2A can take quite a long time.

I don't mind the 10 hours it takes for my 19.1Ah battery to charge at 2A, if it's safer.

Soldering was not too bad, no dry joints and not too much spatter, although there were a few blobs that could come loose in use:

I'm find the sight of those blobs quite alarming, and am suddenly quite tempted to open my charger for a looksie.

 

[WheezyRider]

Most of the time 2A is fine, but I do find occasions where I need to get home and then be off out again fairly soon after and 2A is not enough to put a decent amount of juice back into the pack in time.

If your charger is from Bafang and under warranty, I'd leave it. If it is a generic charger and you can get it apart easily, I think it's a good idea. There have been many cases where I've opened up chargers and found issues like dry joints, solder spatter etc. A friend of mine will often open up PSUs and fit a fan and add holes to them if they are not already fitted.

 

[peterjd]

I am interested in the pros and cons of fast charging in relation to the Bosch fast charger I had to buy to replace a failed original charger for the 36V lawnmower batteries which I also sometimes use for my adapted Swytch mk1 bike when I don't want the weight of the Yose 10.x battery on the rack. There are no warnings that I have seen from Bosch that the fast charge using the new charger is detrimental to battery life. Peter

 

[WheezyRider]

I am interested in the pros and cons of fast charging in relation to the Bosch fast charger I had to buy to replace a failed original charger for the 36V lawnmower batteries which I also sometimes use for my adapted Swytch mk1 bike when I don't want the weight of the Yose 10.x battery on the rack. There are no warnings that I have seen from Bosch that the fast charge using the new charger is detrimental to battery life. Peter

Not sure on the size of your particular Bosch battery, if it is 4 Ah or 6Ah, there will be more than one cell in parallel, so the charging current will be split between more than one cell and I don't know what the current rating of your charger is. Generally it's a good idea not to charge 18650 cells at much more than about 1 A per cell to ensure a long life. Higher currents generate more heat and also the electrode has to change dimensions considerably between charge and discharge, so rapid charging puts physical strain on the battery internals. Bosch probably don't want to advertise that rapid charging may cause shorter cycle life. They want to advertise the convenience of having a tool ready as soon as possible, not that the no. of cycles may go down from 500 to 300. For most tool users, 300 cycles represents years of use. My battery power drill I only have to recharge once a month, so for me, 300 cycles is about forever But if you are in the trade, using tools all the time you'd have to recharge every day, then it's a balance of how quickly do you want your tool to be ready to go, verses battery lifetime.

Very interested to see how you have adapted the Bosch battery to your bike and there are several others here interested in the same, can you post photos?

 

[peterjd]

The fast Bosch charger (GAL 3680 CV) is labelled 8A DC and the original (AL 3640 CV) is labelled 4A DC. The original batteries are labelled 10INR18 /65-2 36V 2.6Ah 93.6Wh and an Exmate compatible which I bought 36V / 5000mAh. They all appear to have charged correctly each charger.

Regarding their use on my modified Swytch bike I can't at this moment lay my hands on the plug adaptor (having been away for a week with my more suitable Decathlon electric on the Rebellion Way circuit of Norfolk) but it consists of two chunky banana plugs (red and black) with one 'blade' removed from each and the other 'blade' filed down to push tightly into the sprung slots of the battery. I am very careful when fitting to observe correct polarity. I'll post some pictures when I lay my hands on it again. Thanks Peter

 

[WheezyRider]

The fast Bosch charger (GAL 3680 CV) is labelled 8A DC and the original (AL 3640 CV) is labelled 4A DC. The original batteries are labelled 10INR18 /65-2 36V 2.6Ah 93.6Wh and an Exmate compatible which I bought 36V / 5000mAh. They all appear to have charged correctly each charger.

Regarding their use on my modified Swytch bike I can't at this moment lay my hands on the plug adaptor (having been away for a week with my more suitable Decathlon electric on the Rebellion Way circuit of Norfolk) but it consists of two chunky banana plugs (red and black) with one 'blade' removed from each and the other 'blade' filed down to push tightly into the sprung slots of the battery. I am very careful when fitting to observe correct polarity. I'll post some pictures when I lay my hands on it again. Thanks Peter

Thanks for the info, looking forward to seeing the pics

8 A, wow, that is a lot for a small battery. 2.6 Ah is probably two parallel strings of 10x 1.3 Ah cells, meaning 4 amps per string. In this video @StuartsProjects posted yesterday, it looks like they are Samsung 1300 cells. Their max charging spec is 4 A, so that is right on the limit (see data sheet link below video):

https://baterie18650.pl/wp-content/uploads/2020/04/13Q.pdf

It is an interesting video as there is no apparent balancing system and no over or under voltage protection at the individual cell level, yet they are driving it at 4 Amps charge...

Well, when the cells fail you can always recell it with decent 3.5 Ah cells and make it a respectable 7 Ah pack.

On the bike, what sort of range do you get with 2.6 Ah?

 

[peterjd]

Here are some quick pics. Its all a bit 'Heath-Robinson', I know, but it does work. I don't know the range but it has kept assisting on, for what amounts to hills around here (S leicestershire), on ~15mile U3A rides. For short shopping trips I usually just slip the attached battery into a pannier. The battery holder is for the Yose 10.x Ah battery which is good for the round trip to Leicester of ~ 30 miles coming back via Wistow Rural Centre. Peter

 

[StuartsProjects]

Many thanks for posting that.

Whilst you need some protusions\slots to keep the battery in place, if its mounted vertical, you could imagine making up a block of nylon or similar which had the holes to take that type of blade terminal.

Or just some type of blade terminal that you could secure to a backplate.

Interesting.

 

[WheezyRider]

Many thanks for posting that.

Whilst you need some protusions\slots to keep the battery in place, if its mounted vertical, you could imagine making up a block of nylon or similar which had the holes to take that type of blade terminal.

Or just some type of blade terminal that you could secure to a backplate.

Interesting.

Maybe we need to start a new thread for "Bosch tool battery powered bikes", seems like it has legs, or should I say wheels?

 

[WheezyRider]

Here are some quick pics. Its all a bit 'Heath-Robinson', I know, but it does work. I don't know the range but it has kept assisting on, for what amounts to hills around here (S leicestershire), on ~15mile U3A rides. For short shopping trips I usually just slip the attached battery into a pannier. The battery holder is for the Yose 10.x Ah battery which is good for the round trip to Leicester of ~ 30 miles coming back via Wistow Rural Centre. PeterView attachment 53100View attachment 53101View attachment 53102View attachment 53103View attachment 53104View attachment 53105View attachment 53106

I love that. 3 options in one on a bike you've probably owned for years? Nice.