Hi,

 

Please can anyone recommend a reasonably priced quality charger for a 36v 20ah pack.

In an ideal world I would buy a Grin Technologies Satiator but they are pretty expensive.

 

There seem to be loads of cheap plastic chargers out there that I would not trust.

 

Ideally I am looking for a UK/EU supplier.

 

Thanks in advance,

 

Robert

Hi,

 

Please can anyone recommend a reasonably priced quality charger for a 36v 20ah pack.

In an ideal world I would buy a Grin Technologies Satiator but they are pretty expensive.

 

There seem to be loads of cheap plastic chargers out there that I would not trust.

 

Ideally I am looking for a UK/EU supplier.

 

Thanks in advance,

 

Robert

 

Hi Robert

 

I'm a tad confused by the post if i'm honest ! That grin product is designed for use with amyriad of different batteries and cells

 

It sounds like have just one? So just buy suitable charger

 

 

what's wrong a plastic casing per se? Used by tens of thousands without issue ?

 

Having said that faster chargers do tend to have larger metal cases and fans to remove heat

 

personally up to 2a seems fine in plastic and over that better with a fan

 

Take a look at BMS battery maybe. My 4a , metal case fan charger came from them

 

But fast charging reduces the life expectancy of the battery pack. Something to bear in mind .

 

I've been in this forum for quite a few years and standard plastic chargers are not something that generally goes wrong. It's pretty much everything else [emoji3]

 

 

 

 

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https://bmsbattery.com/search?controller=search&orderby=position&orderway=desc&search_query=Charger&submit_search=

 

 

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Or in UK call Jimmy at bga

 

https://bga-reworking.co.uk/product/king-pan-insat-li-ion-ebike-battery-chargers-29-4v-42-0v-54-6v-84-0v/

 

 

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Our friend Jimmy ( battery rebuilds) at Insat Int. sells a range of chargers. I'm sure he stands by the products he sells.

 

https://www.ebay.co.uk/itm/King-Pan-Insat-Li-ion-Ebike-Battery-Chargers-29-4V-42-0V-54-6V-2A-84V-4A/331705055471?hash=item4d3b2978ef%3Am%3Am75XTR7nazgCxbCBoW-77mA&var=540907825070

Worth stating that myself and wheeliepete are talking about same business (insat /bga reworking) !

 

 

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Sorry Kirstin, missed your post, too busy typing! That Jimmy is everywhere:D

 

https://ebikebatteries.co.uk/product-category/chargers/36v-chargers/

Thank you both,

 

The reason that I am uncomfortable with the plastic case charger that I have is that the case gets up to 75 degrees C. It works perfectly and is really compact and lightweight to carry but I don't have any confidence in any device that appears to be running under that much stress.

 

My thinking is that a metal charger body will conduct heat and could be used as a heat sink. The addition of a fan reduces the stress on the components significantly.

 

Ideally, I'd like to be able to vary the voltage and the charge rate (down as well as up) 20ah allows me to charge to <90% for local trips and being able to charge at the occasional 3A would allow a boost at lunch time when touring.

 

My plastic charger could run for many hours without a problem or it could fail and catch fire or destroy the battery.

 

Maybe I'm over analysing?

 

Best regards,

 

Robert

Those plastic chargers are designed to run hot, but I agree, it is a bit alarming how hot they do get. Some on here has modified them with taller feet an some venalation holes. Adjustable switching power supplies can be used as CCCV chargers and have the functions you want. These Gophert ones have a pretty good reputation.

 

https://www.ebay.co.uk/itm/DC-60V-5A-Precision-Compact-Adjustable-Digital-Switching-Power-Supply-110-220V/311068842937

 

Comes in 3 and 10 amp versions as well.

I modded my Sans Plastic chargers and they run a lot cooler now, I added about a dozen 8 - 10mm holes all over to aid airflow and cooling.

Edited September 22, 20187 yr by Nealh

Those plastic chargers are designed to run hot, but I agree, it is a bit alarming how hot they do get. Some on here has modified them with taller feet an some venalation holes. Adjustable switching power supplies can be used as CCCV chargers and have the functions you want. These Gophert ones have a pretty good reputation.

 

https://www.ebay.co.uk/itm/DC-60V-5A-Precision-Compact-Adjustable-Digital-Switching-Power-Supply-110-220V/311068842937

 

Comes in 3 and 10 amp versions as well.

Thanks, I like the idea as it would also double up as a bench power supply. I haven't got my head around exactly what CCCV means. I am probably being a bit dim! Does it mean fixed voltage and limited current (i.e. 42V limited to <= XA)? If I use a power supply as a charger I assume that the battery will be charged when the current drops to 0A. I notice that my plastic charger is cooler as the battery nears full charge. I assume that this is because the current is tailing off.

 

Assuming that I have got this right (big assumption) I would use a power supply to charge my 36V pack by setting the output to 42V for 100% capacity and the current to the max I want to charge (nominally 2A). If I wanted to charge to 90% capacity I would set the voltage lower (e.g. 40V). Would I be right in thinking that the BMS balances the cells at the end of the charge cycle? If this is right not fully charging could cause balancing issues?

 

Sorry for my limited knowledge.

 

Robert

I modded my Sans Plastic chargers and they run a lot cooler now, I added about a dozen 12mm holes all over to aid airflow and cooling.

Thanks, how did you know where to drill the holes and how did you aviod damaging the internals when you drilled them?

 

Best regards,

 

Robert

4 screws to separate, remove rubber feet bungs to access.

I only drilled the top part with no electronics to prevent damage, two at each end either side of cable entry's for through venting and 6 - 8 on top exposing heat sink and 2 on the side.

You can also driil one the above the voltage regulator port to allow for voltage adjustment if needed.

Yes, balancing happens at the end of the charge cycle so part charging can result in imbalance.

Balancing in the main is about 41.5 - 41.8v depending on the bms software.

If not balance charging good cells should remain in check but also will be down to how well the battery has been welded/connected together.

A full charge every 4 - 6 uses should make sure all is well.

4 screws to separate, remove rubber feet bungs to access.

I only drilled the top part with no electronics to prevent damage, two at each end either side of cable entry's for through venting and 6 - 8 on top exposing heat sink and 2 on the side.

You can also driil one the above the voltage regulator port to allow for voltage adjustment if needed.

Brilliant, now I understand, my charger is welded/glued together which is why I was a bit confused.

 

Thanks

Balancing in the main is about 41.5 - 41.8v depending on the bms software.

If not balance charging good cells should remain in check but also will be down to how well the battery has been welded/connected together.

A full charge every 4 - 6 uses should make sure all is well.

Thanks, I guess the other alternative for local use is to charge fully but not re-charge until the remaining charge is too low for the next journey so I reduce the number of charge cycles and fully charge each time. Or I could do both :-)

I'd say charge it and use it. The number of charging cycles quoted is full cycles, empty to full. Li-ion batteries don't suffer from partial charges, in fact may benefit because initial charge current is slightly lower and at a high for a shorter period. So anything 14 miles and above, I charge (14Ah battery).

Assuming that I have got this right (big assumption) I would use a power supply to charge my 36V pack by setting the output to 42V for 100% capacity and the current to the max I want to charge (nominally 2A). If I wanted to charge to 90% capacity I would set the voltage lower (e.g. 40V). Would I be right in thinking that the BMS balances the cells at the end of the charge cycle? If this is right not fully charging could cause balancing issues?

no, don't do that.

Lithium ion batteries need to be charged at constant current first, then when the battery is 90%+ full, switch over to constant voltage to finish. The BMS rebalances the cell pack when the battery is 99% full.

Typically, Lithium Nickel Cobalt Aluminum Oxide cells need at least 4-6 hours for a full charge. You can charge faster but you will shorten the cell life. LiFePO4 can be fast charged in 2 hours.

If you want to build your own charger for a 36V battery, you need to program your PSU to be a current source between 31V and 40V with preset current to suit your battery chemistry and capacity (2A for 10AH). Then when the voltage reaches 40V, switch over to float voltage , to rise slowly from 40V to 42V in 1 hour.

no, don't do that.

Lithium ion batteries need to be charged at constant current first, then when the battery is 90%+ full, switch over to constant voltage to finish. The BMS rebalances the cell pack when the battery is 99% full.

Typically, Lithium Nickel Cobalt Aluminum Oxide cells need at least 4-6 hours for a full charge. You can charge faster but you will shorten the cell life. LiFePO4 can be fast charged in 2 hours.

If you want to build your own charger for a 36V battery, you need to program your PSU to be a current source between 31V and 40V with preset current to suit your battery chemistry and capacity (2A for 10AH). Then when the voltage reaches 40V, switch over to float voltage , to rise slowly from 40V to 42V in 1 hour.

Thank you,

 

That fits with the research I did this afternoon. I recon I am much better off with a good quality Li-ion charger at 2A than trying to use a power supply. I've read in a few places that the charger needs to be tailored to the battery (i.e. not all Li-Ion cells use the same charge profile) my current charger is 42V, 2A. Will any 42V 2A Li-Ion charger match the battery?

What should determine the size of charger is the parallel configuration of the battery. A battery with 5 or more cells in parallel will have a maximum charge of 800mAmps per cell which any cell likely to be used these days should be perfectly happy with. Otherwise a battery with say 10ahr capacity is likely to be made from Samsung 25R cells in a 4P - 4 parallel cells - arrangement and that handles a 4 amp charge but a 2 amp charger would be better.

 

For your application which must be in excess of 6P a 4 amp charger is going to take at least 5 hours and 10 hours if 2 amps. Assuming the cells are Li-Ion.

 

The exception to this is a non-uniform cell structure in a battery pack. A mixture of different capacities virtually dictates you use a low amperage charger because the battery management system uses very small balancing currents which won’t allow the BMS to balance charge fast enough - it chucks too much current at it.

 

The same applies to packs which use sub-standard cells. When a Chinese pack is offered at a very cheap price that is generally too good to be true.

 

The answer is build your own then you know what you’ve got but if you can’t, buy from a reputable UK supplier.

25R is one of the top cells with a 20a rating, I doubt that many common 10ah batteries would have these inside.

You’re confusing maximum output with rated capacity. The OP describes rated capacity of 20AmpHr

What should determine the size of charger is the parallel configuration of the battery. A battery with 5 or more cells in parallel will have a maximum charge of 800mAmps per cell which any cell likely to be used these days should be perfectly happy with. Otherwise a battery with say 10ahr capacity is likely to be made from Samsung 25R cells in a 4P - 4 parallel cells - arrangement and that handles a 4 amp charge but a 2 amp charger would be better.

 

For your application which must be in excess of 6P a 4 amp charger is going to take at least 5 hours and 10 hours if 2 amps. Assuming the cells are Li-Ion.

 

The exception to this is a non-uniform cell structure in a battery pack. A mixture of different capacities virtually dictates you use a low amperage charger because the battery management system uses very small balancing currents which won’t allow the BMS to balance charge fast enough - it chucks too much current at it.

 

The same applies to packs which use sub-standard cells. When a Chinese pack is offered at a very cheap price that is generally too good to be true.

 

The answer is build your own then you know what you’ve got but if you can’t, buy from a reputable UK supplier.

 

Hi Douglas,

 

I used to be a fairly dab hand with a soldering iron and am reasonably confident in building a charger (though I've not had much experience of surface mount components and multiple layer boards). I am not up to designing one.

 

Where would I start (kit or pcb template to photo etch)?

 

Thanks for your help,

 

Rob

Rob, I’m referring to building your own battery packs not chargers. I’ve used AnnPower (AliExpress) 4 amp chargers for several years without any trouble. I couldn’t build one for the £30-40 they charge for them. Building battery packs is more testing and mechanical engineering (keeping the cells in place) than electronics.