Charger recommendation

[RogerA]

I'm after recommendations for a decent 42V charger.

My current one seems to have started charging to 42.1V, which I imagine is bad for the battery.

I'm sure it's the charger and not my meter since the battery has recently started showing 42.1V on the display when fully charged (it used to show 42.0), plus the charger reads 42.1V on my multimeter when I test it, whereas the charger for my wife's bike reads 42.0V on the same multimeter.

I know there are a lot of cheap chargers on Ebay, but I'd rather pay a bit more for something that is known to be safe and reliable. If the output current is adjustable to allow me to charge a bit faster occasionally if I'm in a hurry then that would be great, but if not, then a 2A current is what I need.

 

[Cisco-man]

I can’t think that 42.1v is an issue. A 0.2% variance on a standard multimeter (or anything else electrical) is nothing to worry about. Others might disagree though…

 

[AntonyC]

+1. A better way to cater for being in a hurry is to leave the battery charged to around 60% so that there's less to top up when it's needed, a basic socket timer is useful for that. A substantially higher charge current may not be good for the cells and it's less effective at higher State of Charge.

 

[RogerA]

Maybe 42.1V isn't an issue, but if the charger is increasing its output voltage then I'd rather replace it now than hope it doesn't get worse and overstress the battery.

I don't intend faster charging all the time, but would like the possibility of charging at 3A, which is the stated max charge rate of the battery if I need.
I don't charge the battery when I'm not there, which is what I assume you use a timer for, but if I've ridden 50 miles on one day and am going to use it again the following day, then it would be handy to be able to give it a faster charge than usual.

I'm not really after reasons to not buy a charger though. I want to buy one, and would like recommendations of a safe and reliable one.

 

[Cisco-man]

The thing is, the best chargers are now made in China, and the worst chargers are made there too. You don’t necessarily have a mainsteam manufacturer’s name to make the choice by, and the price is absolutely no indicator of quality either. Tread carefully!

 

[guerney]

I'm sure it's the charger and not my meter since the battery has recently started showing 42.1V on the display when fully charged (it used to show 42.0), plus the charger reads 42.1V on my multimeter when I test it, whereas the charger for my wife's bike reads 42.0V on the same multimeter.

My DPC-18 display is all over the place measuring battery voltage. It used to display higher voltage than my reasonably accurate...

https://www.pedelecs.co.uk/forum/threads/checking-multimeter-calibration-at-home.45965/

...Neoteck DM4000 PRO and ANENG 8008 multimeters, but now it displays a lower voltage. I'm wondering if it's to do with colder weather. Right now the display is showing 36.3V, but the ANENG 8008 says my battery's voltage measures 36.45V. Usually there's a bigger difference.

 

[thelarkbox]

If your confident in your Mrs's charger why not just borrow that when not in use? if a different connector is used a few quid spent on ebay/amazon/ali-express connectors and 20 minutes with a soldering iron and shrink fit tube is a lot cheaper than a charger.

the basic 'tool' to shave off a known voltage from a dc supply is the Voltage Divider and didnt you know there is an online calculator to work out the resistors required linky#2

drop the 42.1v to something like 41.5v with a couple of resistors and check the source isnt creeping up every week or so and rest easy perhaps ?

 

[saneagle]

I'm after recommendations for a decent 42V charger.

My current one seems to have started charging to 42.1V, which I imagine is bad for the battery.

I'm sure it's the charger and not my meter since the battery has recently started showing 42.1V on the display when fully charged (it used to show 42.0), plus the charger reads 42.1V on my multimeter when I test it, whereas the charger for my wife's bike reads 42.0V on the same multimeter.

I know there are a lot of cheap chargers on Ebay, but I'd rather pay a bit more for something that is known to be safe and reliable. If the output current is adjustable to allow me to charge a bit faster occasionally if I'm in a hurry then that would be great, but if not, then a 2A current is what I need.

42.1v doesn't matter. It will drop soon after you take it off the charger because the balancing system will drain any high cells.

 

[Cisco-man]

I don’t think that there is a charger out there that’ll give you 42v smack on the nose every time. You might buy something “worse” than you currently have. What charger and battery arrangement do you currently have?

 

[AntonyC]

At the price point for 3A chargers selectable current is unlikely but you should find one with a voltage trimmer to cover future drift. The shopping (and price) advice is so true that oddly it's best to view a charger as a short life consumer good: make the best of it and replace when it fails.

For your normal rate charger all the comments above apply, although a Schottky diode would drop the voltage better (because as the charge current tails off towards zero so does a resistor's dropping effect). A timer lets you charge from 1/5 battery leds to 3/5 once you know how long a full charge takes.

It's certainly good to nip issues in the bud but all we know is that your wife's charger is the right side of 42.05 and yours isn't -- there may be very little in it. Your meter accuracy is probably worse than 0.5% aka 0.2V, with age, cold and an acceptable price tag the charger and BMS are probably no better but the headroom built into them should take care of it.

 

[AntonyC]

42.1v doesn't matter. It will drop soon after you take it off the charger because the balancing system will drain any high cells.

True but perhaps not something to rely on.
Edit: For 42.1V it hardly matters, but perhaps not an approach to rely on generally.

If the charger provided, say, 44V and the BMS just carried on draining, and so the charger didn't see a small enough current to trigger cut off, and the user left the charger assuming it would terminate, the cells could sit at 4.4V long enough to be harmed and eventually unsafe.

I'll say it for you: that's a lot of IFs... but this is consumer electronics (and the common 'wrong charger' voltage would be 54V).

 

[Benjahmin]

I've got one of these:

36v – 42v 10S – eBike Batteries

ebikebatteries.co.uk

Seems to be a very well made charger which doesn't get as hot as others I've got. Bit more expensive but has a quality feel. Output voltage is trimmable via internal pot.

 

[saneagle]

True but perhaps not something to rely on.

If the charger provided, say, 44V and the BMS just carried on draining, and so the charger didn't see a small enough current to trigger cut off, and the user left the charger assuming it would terminate, the cells could sit at 4.4V long enough to be harmed and eventually unsafe.

I'll say it for you: that's a lot of IFs... but this is consumer electronics (and the common 'wrong charger' voltage would be 54V).

42.1v is 0.01v over recommended voltage per cell. OP's voltmeter is not accurate enough for that to make a difference.

When a supplier makes a specification for a cell, like max charge voltage 4.2v, it's not a live or die situation. It's a continuum. the further away from some arbitrary value, the more likely there will be some detriment. It's not an exact science. 0.01v will make approximately zero difference. The specification actually says 4.20v +/- 0.05v, so 4.21v is well within the specification. They could have just as easily chose 4.22v as the specification, but they chose 4.20 because it's a rounder number.

 

[AntonyC]

Amended.

 

[saneagle]

Amended.

Thanks. These sort of threads get my goat. 99% of ebike owners never check the voltage of their chargers and they're completely happy and never have problems, then one guy checks with an uncalibrated meter and finds his 0.1v over, still well within the specification, and everybody goes nuts, scaring him to death and making him panic into buying things he doesn't need. This sort of thing happens too much on this forum, like the other thread scaring the guys into not fitting a motor because its a little bit wider than their frame. Safety is paramount, but this is just histeria.

 

[AntonyC]

You got it mate, a boring "Can you recommend..." thread is just begging for trolling innit

<-- smiley

 

[Nealh]

Depending on the charger type some have a volatage pot inside that is adjustable , if one is really concerned because of a small insignificant reading then oepn it to have a look. Tbh as as has been said it is neither here or there 0.01v.

 

[AntonyC]

(Obligatory advice to don washing up gloves when opening an unplugged charger in case of stored mains voltage.)