Plug charger first into e-bike battery and then wall socket, or vice versa? (or it doesn't matter?)

Sophie777

Active member
Jul 3, 2018
215
107
Canada
Since the e-bike fire on the Toronto subway, I've been concerned about the safety of storing and charging my Bosch Trek Powerfly battery inside my apartment.

One of the causes of e-bike fires according to the Toronto Fire Department is "incorrect charging"; they say to follow "manufacturer instructions".

I always thought for some reason we are supposed to plug the charger into the wall socket first, and then the battery.
Now I am finding contradictory information: some manufacturers say to do the reverse (plug the charger into the battery first).

I checked my Bosch manuals for my charger and battery. Neither are clear about which to do first. However the illustrations in the manual for the charger shows the charger being plugged into the wall socket first; the illustrations in the manual for the battery show the opposite.

Is there a consensus in the interest of maximum safety as to whether the charger should first be plugged into the wall socket or first into the e-bike battery?
 

ThierryGTLTS

Member
Feb 17, 2020
120
56
Belgium
Yes, Wall first, then Battery.

This is truth for most "e-bike chargers".

For low voltage chargers (Phones, cameras,...) it doesn't matter.

Have a Nice Day.

Thierry
 

Mikerb

E*POWAH Elite World Champion
May 16, 2019
6,565
5,057
Weymouth
it depends whether the wall socket being used is switched or not. If the wall socket is unswitched ( ie live) you should plug the charger into the bike/battery first, then the wall. If the wall socket is switched it does not matter which you do first as long as the wall socket is switched off.........switch on when everything is connected. The reason for this procedure is that you do not want to be plugging a charger into the bike when there is voltage running through it because that can cause arcing as you bring the contacts points together. That can damage the contacts or in a worse case scenario start a fire if there is flammable material nearby. The same applies to in all cases of connecting electrical components not just bike chargers.
 

Planemo

E*POWAH Elite
Mar 12, 2021
605
706
Essex UK
For most of the well known ebike systems out there (Bosch/Yamaha etc) made in the last 5+ years or so it really doesn't matter. This is one of the joys (and unfortunately, cost) of having a properly engineered system unlike the cheap shite. Decent stuff will not have hot battery ports and everything has to handshake and systems/health be checked/ratified before any charging happens. That said, I always plug the charger in first but only because of habit.

On badly designed stuff (like older e-unicycles that I used to use) you would HAVE to have the charger plugged in first otherwise the hot battery port output (circa 100v) being shoved into an unplugged charger would spark enough to skid your pants.
 

Streddaz

Active member
Jul 7, 2022
300
427
Tasmania
I read this before...
Always remember to plug the charger first into the wall outlet this is because most of the chargers have capacitors that condition the power during charging and what happens if you plug the charger into the battery without plug in the charger in the wall outlet first is the current will flow from the battery back into the charger capacitors and in this case, you will see a spark.
And that lines up with what specialized instructs.
Specialized say to plug the charger into to wall first and then the bike/battery.

But then Shimano says the opposite...
And so does Bosch.
1704397185485.png


I'd go with what your manufacturer recommends and that covers your arse.
 

sethimus

Member
Dec 31, 2023
127
114
Switzerland
it depends whether the wall socket being used is switched or not. If the wall socket is unswitched ( ie live) you should plug the charger into the bike/battery first, then the wall. If the wall socket is switched it does not matter which you do first as long as the wall socket is switched off.........switch on when everything is connected. The reason for this procedure is that you do not want to be plugging a charger into the bike when there is voltage running through it because that can cause arcing as you bring the contacts points together. That can damage the contacts or in a worse case scenario start a fire if there is flammable material nearby. The same applies to in all cases of connecting electrical components not just bike chargers.
this is a german product, we have laws over here, unlike the us. do you really think there is no protection build in in these chargers? they run on 240v all over europe…
 

Sophie777

Active member
Jul 3, 2018
215
107
Canada
View attachment 131810

I'd go with what your manufacturer recommends and that covers your arse.
I have the same Bosch manual for my battery.
But the manual for my Bosch charger suggests the opposite:

Bosch charger - initial operation.png


Bosch charger - charging the removed battery.png


So here in the manual for the charger, Bosch suggests the first ("initial") step is to plug the charger into the wall, which seems to contradict what's written in the manual for the battery.
 

Ark

Active member
Mar 8, 2023
460
386
Newcastle Upon Tyne
So here in the manual for the charger, Bosch suggests the first ("initial") step is to plug the charger into the wall, which seems to contradict what's written in the manual for the battery.
If you use a socket with a switch then your connecting the battery before you switch on the power.

Any claims of the capacitors in the charger needing full constant charge to condition the battery is speaking nonsense.
The conditioning happens at the very end of the charge when the battery says 100%
The charger will auto turn off when its finished balancing the cells.

You don't need to balance the cells every charge or anything like that, just 1-2 x a year if you use your bike often.

You guys really think Bosch etc would design a charger that doesn't take into account people connecting either end first?
you really think they wouldn't have the batteries switch off with enough charge in the cells to safely fill any capcitor in the charger without risk?
 
Last edited:

Brian VT USA

Member
Oct 2, 2023
94
67
VT, USA
It seems that maybe the best bet is to have your electricity coming from a power supply with a switch that is turned off?
Connect everything and then turn the power supply switch on?
I dunno. My (Luna) charger says to plug the charger in before connecting the battery.
 

Suns_PSD

Active member
Jul 12, 2022
522
438
Austin
Always plug in the battery to the charger first. Then plug the charger into the wall.

If you insert a plug or even just turn on a wall switch in the dark is not uncommon to see a small blue spark as the electricity makes a leap. You don't want that spark at your battery.
 

TimC7

Ovine Assaulter
Apr 22, 2023
272
1,059
UK
Always plug in the battery to the charger first. Then plug the charger into the wall.

If you insert a plug or even just turn on a wall switch in the dark is not uncommon to see a small blue spark as the electricity makes a leap. You don't want that spark at your battery.
High voltage side is insulated from low voltage side plus plenty of smoothing - plug everything before powering up. Bike first if the mains is unswitched.
 

Sophie777

Active member
Jul 3, 2018
215
107
Canada
Any claims of the capacitors in the charger needing full constant charge to condition the battery is speaking nonsense.
I guess this is the question: is it true capacitors in the charger need to be charged first in order to avoid causing a spark at the battery when connecting to the battery?

If yes, then wall first.
If no, it doesn't matter?
 

Brian VT USA

Member
Oct 2, 2023
94
67
VT, USA
I guess this is the question: is it true capacitors in the charger need to be charged first in order to avoid causing a spark at the battery when connecting to the battery?

If yes, then wall first.
If no, it doesn't matter?
I believe this is the case with my Luna charger. Capacitor(s) need to be charged first (from the wall power) before connecting to the battery.
 

Mikerb

E*POWAH Elite World Champion
May 16, 2019
6,565
5,057
Weymouth
I did some research on this both in Ebike specific articles and general electronics type articles and forums. If you do that you will find as many variations of opinions as in this post!!
What does seem to be a common theme is the role that capacitors play in the transformer and I would say the most convincing verdict is that with a properly designed/modern charger it does not matter what order of connection you use. That simply because the design of the charger includes circuits that provide protection for either order of connection. The exception to that would appear to be older equipment and potentially even modern Chinese charger products.

I have 3 chargers....2 Bosch and 1 Cube. None of the chargers include any information a bout connection order on labels on the back......just statements a bout voltages ( input/output). In my opinion if a specific order of connection was required, it would be stated actually on the charger, not only in a manual which very few are likely to refer to after the first use!
I also read of others who said their bike manual inferred the opposite connection order to their charger manual.............in reality if those instrcutions in either were about adhering to a specfic sequence as opposed to merely how to connect the charger, charger lead, charger socket together, it would be marked with a specific red flag warning.

Personally, for all aspect of electrical connection, including the process of charging my bike, I make all connections before switching on the mains. I have being doing that on 3 bikes for over 4 years with no charger or battery problems.
 

Plummet

Flash Git
Mar 16, 2023
1,152
1,634
New Zealand
Same here. I connect charger to wall socket, then to battery, then turn the wall socket on.
There isn't any switches on either chargers I have (bosch and shimano). Therefor the switching needs to take place at the wall.

Plugging a charger into live socket or pluging a live charger into a battery could potentially lead to a voltage/amperage spike and or sparking damage at the plugs that would lead to a potential failure.

With that said, the smarts in the battery and the charger should allow for powered up plugging in.
 

Sophie777

Active member
Jul 3, 2018
215
107
Canada
Same here. I connect charger to wall socket, then to battery, then turn the wall socket on.
There isn't any switches on either chargers I have (bosch and shimano). Therefor the switching needs to take place at the wall.

I don't have a switch on my wall socket; would it be okay to connect the Bosch charger to a surge protector - which I can turn on and off?

The reason I ask is that Bosch says in their manuals not to use "extension cords".
 

Brian VT USA

Member
Oct 2, 2023
94
67
VT, USA
I don't have a switch on my wall socket; would it be okay to connect the Bosch charger to a surge protector - which I can turn on and off?

The reason I ask is that Bosch says in their manuals not to use "extension cords".
That's what I would do. It's better than the alternative and it's likely a short "extension" cord with heavy gauge wire that can handle the current.
 

Brian VT USA

Member
Oct 2, 2023
94
67
VT, USA
I don't know much about electricity, but capacitors store electricity. If the capacitor(s) in a charger lose some of their charge over time then if you connect the charger to the battery before the wall then the capacitor will try to draw it's needed charge from the battery (not good). I think that's how Luna explained their reason for plugging their chargers into the wall before connecting them to the battery.
 

2WheelsNot4

E*POWAH Master
Oct 17, 2021
918
712
Scotland
I first plug the charger into the bike, then the charger wall plug into the wall. Theres no 'on' switch on the wall socket.

I do it this was because sometimes the bike socket seems a bit fiddly, and its easier to have it in there first them add the power with the easy to fit 3 pic plug.

I've also never seen a reference as to doing it in a specific order. But on the strength of this thread I'll double check on what the manufacturer says and follow those instructions. Just because I've been doing it one way without problems, doesnt mean its the correct way to do it.

That said, when charging an Exposure light, you are suppose to plug the charger into the wall socket first, then plug the charger lead into the lamp.
 

#lazy

E*POWAH BOSS
Oct 1, 2019
1,408
1,537
Surrey
I’m not having it that it makes any difference whatsoever , in my 50years of existence and at least 45 of plugging I’ve not cared one jot and nothing bad has happened to plug or item plugged in .
However it might have something to do with the Uk using the best 3point plugs and the rest of the world using those useless floppy things ☺️
 

Slymobi

E*POWAH Master
Mar 13, 2021
988
2,550
UK, Derbyshire
I’m not having it that it makes any difference whatsoever , in my 50years of existence and at least 45 of plugging I’ve not cared one jot and nothing bad has happened to plug or item plugged in .
However it might have something to do with the Uk using the best 3point plugs and the rest of the world using those useless floppy things
 
Nov 28, 2023
3
5
Italy
Since the e-bike fire on the Toronto subway, I've been concerned about the safety of storing and charging my Bosch Trek Powerfly battery inside my apartment.

One of the causes of e-bike fires according to the Toronto Fire Department is "incorrect charging"; they say to follow "manufacturer instructions".

I always thought for some reason we are supposed to plug the charger into the wall socket first, and then the battery.
Now I am finding contradictory information: some manufacturers say to do the reverse (plug the charger into the battery first).

I checked my Bosch manuals for my charger and battery. Neither are clear about which to do first. However the illustrations in the manual for the charger shows the charger being plugged into the wall socket first; the illustrations in the manual for the battery show the opposite.

Is there a consensus in the interest of maximum safety as to whether the charger should first be plugged into the wall socket or first into the e-bike battery?
For battery storage at home there are specific bags, glass fiber fireproof, not expensive.... 25€ on AliExpress 👍
 

Suns_PSD

Active member
Jul 12, 2022
522
438
Austin
My Fazua 60 owners manual has specific instructions on this.
Like I said, plug in the battery first, then to the wall.
If you have a switched outlet that's fine as you are just transferring the connection, and the possible resultant spark, to the switch. Which is the goal, to keep that away from the battery.
 

Planemo

E*POWAH Elite
Mar 12, 2021
605
706
Essex UK
There isn't any switches on either chargers I have (bosch and shimano). Therefor the switching needs to take place at the wall.

It's immaterial whether theres a switch at the wall or not. The 'actual' switching takes place within the charger, both on the input and output, and it won't turn on any output to the battery until the charger has sorted itself out power-wise, shaken hands with the battery and done a diagnostic check that the battery isn't too low/high on charge, that there isn't any iffy cells etc etc. If you plug the battery in first it makes no difference to the process - the output of the charger won't allow anything into it anyway because it's switched based on the above.

Plugging a charger into live socket or pluging a live charger into a battery could potentially lead to a voltage/amperage spike and or sparking damage at the plugs that would lead to a potential failure.

It won't, for the previous reasons given.

The caveat being any cheap, non branded shite where battery ports are hot and/or there is no comms line to the charger, or input caps aren't protected (switched via mosfet) from 240v surges etc etc. The differences between a Bosch charger and a £20 no-name chinese charger will be immense.

TLDR - for decent systems it makes absolutely no odds how you connect everything up. You have to remember that big manufacturers will design high voltage electrical products that will be utterly infallible even by ham fisted monkeys (most ebikers there then).

But people are of course free to do what they like, follow the manuals etc.
 

Shark58

Active member
Mar 5, 2023
231
167
Germany
The manual for the TQ50 charger clearly states to first plug the charger into the wall outlet and then plug the charger into the battery port. I have no reason to do this differently.

IMG_0352.png IMG_0353.png IMG_0354.png IMG_0355.png
 

kneecap

Member
Sep 10, 2020
21
7
so cal USA
I first plug the charger into the bike, then the charger wall plug into the wall. Theres no 'on' switch on the wall socket.

I do it this was because sometimes the bike socket seems a bit fiddly, and its easier to have it in there first them add the power with the easy to fit 3 pic plug.

I've also never seen a reference as to doing it in a specific order. But on the strength of this thread I'll double check on what the manufacturer says and follow those instructions. Just because I've been doing it one way without problems, doesnt mean its the correct way to do it.

That said, when charging an Exposure light, you are suppose to plug the charger into the wall socket first, then plug the charger lead into the lamp.
I'm with you on this, connection at wall socket is more straightforward compared to the deep battery socket in my levo
 

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