How do you make a switch for the battery box

[schwibsi]

I intend to make a couple of 12s4p boxes of Konion cells, wich I'll mount to my ebike.

To do a proper job, I want to
1. put a 40A fuse in each box
2. outfit them with a switch each to sever the connection to the outside
3. put in low voltage protection
4. maybe voltage meter

The fuse is a no brainer. I'l just solder one on the + lead.
I couldn't find any rocker switches, that can handle 40A other than inudstry grade switches for heavy machinery.
Not knowing too much about electronics, wondering if a mosfet might be the solution to switch off the outlet when not needed.
Could you maybe tell me, if the switch is a stupid idea all together, and if not, what I'd need to do this. Switches for low currents are available in all shapes and sizes so, if I'm on the right track, this shouldn't be too hard to implement. Would this cost a lot of power while switched on?
Low voltage protection. I won't fit a BMS on the Konions because I've read quite a lot about it not being necessary for the Sony cells. However, I will fit a 15pole mini D-Sub socket on the outside of the pack to check the cell drift occasionally and to balance if needed.

For the low voltage protection, would you just go low voltage buzzer or have something actually cut the power, if it goes too low?
Are there any simple electronics that will cut the charging lead for over voltage protection? I would have separate connectors for charging and outlet.

How about a small panel mount voltage meter to show, how the battery is doing? Or is there anything else that would help determining, how much capacity is left or how long charging will still take.

I sincerely apologize, if those questions have been answered before. I did take a long hard look, but a full BMS is not, what I'm looking for, as I don't need balancing for the individual cells. If you could give me pointers, I'd be very grateful

 

[Skedgy Sky]

You don't have to use some industrial switch to turn the batteries off and on.

I use two of these: http://media.diversitech.com/web_image/ED447.jpg

Ratings for things don't necessarily mean the limit of something. ...Just like with hub motors. Kits say "800w hub motor " but they're able to be pushed to a few kilowatts.

However... I did once use a REALLY TINY key switch to turn the bike off and on. It wasn't a problem while riding (because the switch experienced only intermittent bursts of high current, letting it cool down in between)... Until I want to charge. I was using charging through the switch (which went through my $25 hobbyking watt meter) and so the charger was pulling a continuous 30 amps through this small keyswitch. After about 30 minutes the contacts within the switch became hot enough to shift around in the plastic that the switch was made of. Long story short, pushing 30 amps (for 30+ minutes) through a switch that was rated for maybe 1amp at 12v AND was made of plastic, caused it to fail.

It did work, just not for long.

Using a metal switch ($2-3) like the one I posted a link to above is fine as far as I can tell. They may not be rated for what i use them for, but a little excess heat (which you most likely won't notice) from the switch wont hurt stop it from performing as it should.


Monitor voltage using a watt meter of some sort.

 

[schwibsi]

Well, please don't take this the wrong way, but that is something you can absolutely not do in Germany. If you start using electric components that are not rated for what they are supposed to do, you'd be liable for any damages you cause as this is gross neglect.
No insurance company would ever pay, if you burn your house down because you pulled 30A over a switch that was rated for 2A.
The ratings for the motors are one thing. If you destroy a motor, ok, then the motor is broken, but it won't damage anything else. Screwing around with electronics and not taking the precautions required, is extremely dangerous.

I'm not an engineer and I might not know a lot about electric engineering, but that I know.

 

[amberwolf]

If you want electronic switches, there are a number of projects around ES that already can switch it on and off, including Methods' HVC/LVC system's HVC breaker.

Some of the precharge circuits made from FETs coudl also be used to shut off the battery.


The catch is that just about all of the solidstate devices you can use to switch with tend to fail shorted, so if something did go wrong it may well leave the pack connected.


There are a number of contactors (relays) designed to switch voltages and currents at ebike levels and up, that can be controlled with low-voltage low-current switches or electronics. But they usually cost a fair bit.


Circuit-breakers are avaialble in DC voltage and current levels taht ebikes can use, too, but they can get kinda big and costly if you need high currents. Still often are cheaper than switches to do the same thing, just because they are used more often than switches for the purpose, I think.

 

[Holocene]

The technique you need to use is placing a precharge resistor in parallel with your switch. That way, you can avoid the huge momentary current spike when the switch is connected.

Lot's of examples discussed here on the 'Sphere. For example, in this thread:
"Active pre-charge/inrush control"
http://endless-sphere.com/forums/viewtopic.php?f=3&t=40142&p=691871&hilit=precharge+resistor#p691871

Cheers, and keep Grinning! :lol:

 

[ddk]

Automotive switches are your best source for high-current switches.
The current rating of the switch really depends on how much current your controller pulls.
I use 23-30a controllers and my battery switches are rated for 30A, mainly because I like the style of the switch.

Btw, I've also used 20A switches with the same sized controllers with no problems for many years.

The thing is, the switch is not switching 30A when first turning on a controller.
-also-
Automotive switches have to safely work at +60V and above without "flame-on, flash!"
I've tested "12" and "32" Volt switches that have safe operation up to and above 100V. -Even if their voltage rating is "12V'. or "32V"
I'm not sure where that "12V" figure comes from, actually. Maybe a one in 10000 event?- as I only tested a few hundred cycles per switch with it's full rated current load...
back when I did that kind of stuff.

 

[jonescg]

I've been using a 10 A 250 V AC rated toggle switch on my ebike for the last 6000 km and it's been working well. It takes the full 120 amp draw on occasion, but most of the time it sits at about 20-40 amps. So far so good, but I do have a precharge resistor in parallel with it so when I plug the controller in there is no spark.

You could always get a big red breaker.

They're fairly cheap, but a precharge resistor and momentary button is still a good idea.

 

[dnmun]

if your battery has a BMS then you can put a switch in the BMS circuit current and shut off the battery pack by turning off the BMS with a tiny switch.

 

[marty]

Buss SERIES 187 MARINE RATED CIRCUIT BREAKER
25 AMPS to 150 AMPS

Buy at a boat shop.

 

[schwibsi]

Hmmm... with the options I've seen so far, I guess, I'll just have a switch for the main and pre-controller.

I'm not going to use a full-fledged BMS, still need to look into over and under-voltage protection.
Wouldn't a power supply set to to 57.4V and a overvoltage cutoff on the battery be enough to charge, or do I need to get a real charger with a charging program?

 

[biohazardman]

Lots of miles/years on these without problems/failures. http://endless-sphere.com/forums/viewtopic.php?f=3&t=32463

 

[amberwolf]

Wouldn't a power supply set to to 57.4V and a overvoltage cutoff on the battery be enough to charge, or do I need to get a real charger with a charging program?

If the overvoltage (and undervoltage on discharge) is per-cell, it's fine.

But if you don't have per-cell monitoring/cutoff, then you need to check the actual cell voltages yourself once it cuts off for either pack-level LVC or HVC, every time, so you can see how the cells are getting along, staying balanced or not, etc.

Without one or the other, or both, you risk weak cells ending up way over or way under voltage, and the rest of the pack taking up the slack and potentially ending up severely under or overcharged (the opposite of whatever the weak cell(s) are).

 

[schwibsi]

I guess, a reasonable switch is out.

I'll have to switch my DC/DC converters and the controller in the controller box.

Can somebody tell me, where I can get a battery protector suitable for 14s? It only has to have over current cut off and under-voltage cut off on one end and overvoltage cutoff on the other end.
I couldn't find any reasonably priced products. Or can I make that myself somehow?
I will monitor the invidivual cells on the charger. Also the lack of drift of the Konions won't make monitoring every cell at all times necessary.

 

[amberwolf]

Assuming you only mean at pack-level, then if you have a Cycle Analyst you already have a programmable current limit and LVC. HVC you'd have to deal with at the charger, but if it already monitors per-cell then that's better anyway. You don't need an HVC when actually on the bike in-use, unless you're using regen down seriously long hills while still at a high state of charge.

 

[schwibsi]

No, I'm not going to be using a CA. For the first build, I'll use a speedict. and the next one will be an arduino based pre-controller.

Hmm.... maybe as an overcurrent limiter, I could use a fuse that doesn't break but one with a switch, if something like that exists.
The undervoltage is mostly important for me because of the DC/DC converters I am also using, in case I forget to switch them off. I don't want to damage the cells.

As far as charging goes, I wasn't able to find affordable chargers with decent power output. The Bms-battery one does not have a display anymore and to my knowledge does not show, when charging is complete.
I could use a MRNG 900. A 900W power supply that can do 60V and 15A, which would be nice. But I'd be worried somebody touches the and changes the voltage. Without overvoltage protections they might destroy the battery.

 

[schwibsi]

http://www.ebay.de/itm/Sinus-Live-A...tomatiksicherung-NEU-/271012322743#vi-content

Maybe something like that for overcurrent protection, could double as a switch

 

[schwibsi]

How about the smart bms from bms battery?

What's the highest voltage you can set for over-voltage protection and the highest for under-voltage protection?
Does it sever the connection in case of over-currents? If so, maybe the overcurrent protection could be triggered with a switch.

 

[schwibsi]

I just found out the smart-BMS from BMS-battery can be reprogrammed to accept 15A charging current. Seems to be the perfect bang for the buck solution for me then.
Still thinking about what power supply's the best bang for the buck.