Multimeter/Battery Charger/Ebike Issue

IT Loser

Hi there- I recently purchased some decidedly ropey Lithium batteries off ebay.

They are rated at 36v 20Ah and 48v 20Ah respectively.

They each came with a battery charger, 5A rated. I recently got advice from some people here on how to switch the plug over for use in Ireland- thank you.

The terminal on the battery charger which connects to the BMS {Battery Management System} is like your basic 3 point kettle connection.




Thats the terminal, with the probes in it, and the charger in the background with the LED's.

Now the problem starts.

Consider the following pic of the terminal, and note the symbols/writing, denoting Live, Neutral and earth:



Neutral is bottom left marked "N". Live is bottom right, marked "L". Earth, with the international symbol, is on the top of the triangular formation.


Now, I take a Fluke 115 Multimeter {sort of the Rolls Royce of multimeters} and I insert the RED/POS probe into the LIVE slot, the BLACK/NEG probe into the NEUTRAL slot....and what I end up with...is a NEGATIVE READING.







Okay, fotos are a bit big so I will cover the 2nd part of this conundrum in the next post.

IT Loser

As perplexing as this was, I decided to whip open the charger and see if the person who wired it up had not made a mistake.

Here is what I found:-



So they appear to be wired correctly internally.



But then it got even better.

When I examined the BMS that the charger is supposed to plug into [Charger-BMS-Battery]....I found that the positive wire from the BMS was being mated with the neutral/negative terminal on the charger, and that the negative wire from the BMS was being mated with the positive/live terminal from the charger



And then I look at a sticker on the back of the charger and find this absolutely mind-boggling piece of information:-





Please note the "N=+" and "L= -" routine at the bottom of the sticker.

Does anyone have any ideas WTF is going on here?

Thanks.

davelerave

Isn't that an ac link up. The 'iec' socket and plug?

IT Loser

davelerave wrote: »

Isn't that an ac link up. The 'iec' socket and plug?

The only AC aspect of this is when the charger is plugged in to the mains socket.

It then steps down to a suitable voltage for a 36v rated battery.

Thats it.

the link up you are looking at is coming from a BMS which in turn feeds into a 36v 20Ah rated LIFEPO4 battery.

davelerave

the first picture in your second post? ac 230v brown and blue? is that a link or the mains cord i'm a bit confused .sorry

IT Loser

davelerave wrote: »

the first picture in your second post? ac 230v brown and blue?

The internals of the battery charger leading from the power cord of the charger to the PCB of the charger. Those two wires emanate from the power cord and a wired into a 3 pin 5A-fused plug. The transformers on the PCB then step it down to around 44 volts which is transferred to the BMS of the battery via the kettle style plug.

That plug, when tested, returns a negative reading, and it is that negative reading which I am trying to understand.

IT Loser

By way of completing the picture, this image shows the arrangement of the wires as they leave the charger en route to the socket which feeds the BMS/Battery.

As you can see, the live is wired to the board and is directly adjacent to, what looks to my eyes, a "MINUS" sign.

Could this be the problem?

davelerave

Ya no prob . i associate' iec 'plugs with mains only.So it looks like the N pin on the iec socket is positive then(as per the label on back)is it working?
doesn't seem to be a prob there as it corresponds correctly to red and black on BMS iec plug

IT Loser

davelerave wrote: »

Ya no prob . i associate' iec 'plugs with mains only.So it looks like the N pin on the iec socket is positive then(as per the label on back)is it working?

Small correction- its a 3A fuse in the plug.

To answer your question: yes, it "works" fine. I plug it in, the LED's kick into life, the fan whirrs up, and it puts out a steady -44volts or so.

I have not tried to charge the battery with it yet, I just dont fancy introducing a - to a +, but the charger comes to life when it is plugged in.

When you say it "corresponds correctly"...surely pos should lead onto pos and neg onto neg?

What I have here is a negative rating which, it seems, gets switched over thanks to the physical wiring arrangement of the IEC.

davelerave

no. the bms red and blck leads match up correctly to the iec socket on charger by the looks of it

(reverse polarity on the mains cord wouldn't affect the dc polarity anyhow btw)

IT Loser

davelerave wrote: »

no. the bms red and blck leads match up correctly to the iec socket on charger by the looks of it

(reverse polarity on the mains cord wouldn't affect the dc polarity anyhow btw)

Afraid not.....where the BMS meets the IEC, you are definitely going to have a plug marked "L" running onto a black wire and a plug marked "N" running onto a red wire.

I really dont understand it at all. I do not grasp how the device can display a MINUS rating for its voltage output.

davelerave

i can assure you they match:D
N is positive all the way through iec lead into BMS(red wire)

Michael Collins

Any chance of a zoomed out photo of the whole system? It is a bit weird that the N terminal is at a higher potential than the L terminal but then this is a nonstandard use for an IEC connection system, so whoever built it probably didn't care what way they connected it up.

Have you any other reason to think that it won't work, given the batteries and the chargers both came together?

Pete67

Dave has it right, the designer just elected to use the N for the +ve DC supply. It will work fine but is very bad practice to use an IEC connector for low voltage DC, as there is nothing to prevent someone plugging a 230V supply directly to the batteries!

IT Loser

Thanks for your replies fellas.

It seems Dave was right, alright.

The BMS and returns a + reading on voltage once the charger is hooked up to the BMS and the charger is running.

It was also successfully charging the battery.

I have no idea why the people who manufactured it were so shoddy.

@MichaelCollins: here is the flickr link, please indulge yourself- a photo of everything is there.http://www.flickr.com/photos/43650746@N07/?saved=1

Right now, my latest issue is how to connect the neg/pos terminals to the molex-esque arrangement coming from the DC Controller.

Went into a tool shop today and they had NO FEMALE SPADE ENDS:mad::mad: