Yes, I remember those monsters well.
Whoops, I musn't get the credit, it was Fecn who posted that. A number of members have confused our online names, and by an odd co-incidence we live in the same area!
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Battery switch recommendation anyone?
- Thread starter frank9755
- Start date
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Interesting to read these responses - thanks everyone
What I have at the moment are fairly robust connectors (Powerpoles). The reason I was looking for a switch is that I typically get some sparking when connecting, which I felt wasn't ideal, so thought it would be better to separate the actions of connecting and switching. Reading this, it sounds like I should just put up with the odd spark and stick to just having the connector. Fair enough - saved me some work!
PS I remember the old dolly light switches with their heavy click. I liked them so much that when we had our house re-wired I had modern versions of them put in! I didn't know that we used to have DC mains, and that was the reason they had to be so robust - interesting!
What I have at the moment are fairly robust connectors (Powerpoles). The reason I was looking for a switch is that I typically get some sparking when connecting, which I felt wasn't ideal, so thought it would be better to separate the actions of connecting and switching. Reading this, it sounds like I should just put up with the odd spark and stick to just having the connector. Fair enough - saved me some work!
PS I remember the old dolly light switches with their heavy click. I liked them so much that when we had our house re-wired I had modern versions of them put in! I didn't know that we used to have DC mains, and that was the reason they had to be so robust - interesting!
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An improvement to just using a switch....
A suitable metal oxide varistor (MOV) wired across your switch contacts will much reduce the chance of arcing, and will also give your electronics a much better time. I suggest the following RS item (you can view and/or order it on the RS website):
Cat No. 289-7626
This is rated for a maximum supply voltage of 65 volts, so would be in the right sort of range for an e-bike application.
How these work - at up to the rated voltage (or a slightly lower AC voltage, since these devices are bipolar) they conduct almost no current at all (perhaps a few microamps). However, once you get above the maximum rated voltage they do so - not much at first, but (in this case) rising to 100 amps at 135V. They turn off again as soon as the applied voltage drops. Naturally they are only rated at this sort of current for a short time - a couple of milliseconds - but in your application the actual maximum would never exceed the inrush current in any case.
They save your switch contacts and your electronics due to the very fast turn on and turn off time, and the resultant limit on transient voltage which may well never rise above 100V. Basically they 'swallow' the spark in an orderly manner if you get any contact bounce.
If you manage to blow one away (which in my experience is difficult - we use them in numerous applications, and they are amazingly tough) they fail short-circuit so your switch appears to be permanently 'on'.
The item mentioned comes in at 71.6p each in a packet of 5, so won't break the bank. They are about 2cm across, so about the size of a 2p coin.
Rog.
A suitable metal oxide varistor (MOV) wired across your switch contacts will much reduce the chance of arcing, and will also give your electronics a much better time. I suggest the following RS item (you can view and/or order it on the RS website):
Cat No. 289-7626
This is rated for a maximum supply voltage of 65 volts, so would be in the right sort of range for an e-bike application.
How these work - at up to the rated voltage (or a slightly lower AC voltage, since these devices are bipolar) they conduct almost no current at all (perhaps a few microamps). However, once you get above the maximum rated voltage they do so - not much at first, but (in this case) rising to 100 amps at 135V. They turn off again as soon as the applied voltage drops. Naturally they are only rated at this sort of current for a short time - a couple of milliseconds - but in your application the actual maximum would never exceed the inrush current in any case.
They save your switch contacts and your electronics due to the very fast turn on and turn off time, and the resultant limit on transient voltage which may well never rise above 100V. Basically they 'swallow' the spark in an orderly manner if you get any contact bounce.
If you manage to blow one away (which in my experience is difficult - we use them in numerous applications, and they are amazingly tough) they fail short-circuit so your switch appears to be permanently 'on'.
The item mentioned comes in at 71.6p each in a packet of 5, so won't break the bank. They are about 2cm across, so about the size of a 2p coin.
Rog.
I don't see how this could help as the controller is a capacitive rather than inductive load when it is switched on (with throttle off).
I've just seen that the Anderson Powerpole system includes a special contact set that is "first mate, last break". It's intended as a grounding connection for static, etc, problems, but I imagine 2 of them could be rigged up to make a pre-charge circuit for connecting to capacitive loads. I think I'll have to get some and experiment.
BTW, a varistor, transorb, etc might be useful across switch contacts, though you would have to consider the risk of it going short circuit, but there are obvious physical difficulties with using across connector contacts.
Nick
Manufacturer P/N TK-010-GND. RS stock no 382-6158
BTW, a varistor, transorb, etc might be useful across switch contacts, though you would have to consider the risk of it going short circuit, but there are obvious physical difficulties with using across connector contacts.
Nick
Manufacturer P/N TK-010-GND. RS stock no 382-6158
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I used one of those on a battery for a while and thought it was very good.Just to add to what Nick said there. I personally used a 250V, 30A rated Neutrik Speakon connector for my custom battery pack. The connector can be rotated by 15 degrees without being unplugged to achieve an 'off' position and when turned it clicks and locks to the 'on' state.
IMO these are the best connectors in the world ever. No exposed contacts, designed for anything up to mains voltages and massive currents for DC uses. I have wired 5 of these sockets throughout my van as the standard cigarette lighter plugs are pathetic when you're running inverters/laptops etc.
Sorry - what has that got to do with it?
What gives you a spark (possibly) when you close a switch is contact bounce. At the moment of first closure there is NO current flow. As I said, the heavy inrush current required to charge the caps in the controller ramps up from zero over a few microseconds. Then, as the caps charge up, it tails off again - this in the order of milliseconds. If your switch opens due to contact bounce while the inrush current is high, you'll get a spark.
The MOV merely kills most of the voltage developed across the contacts which produce a spark. In dry air it takes a minimum of about 300 volts to produce a spark (but much less to maintain one). When you get one from a switch on a low-voltage circuit it's because you're interrupting a very high (momentary) current, which would like to keep flowing, and kicks up a sizeable transient voltage in attempting to do it. With these sorts of currents, even the wiring between battery and controller has an effect, because any circuit will have some inductance and capacitance, even if it was not intended and it's very small...
I wouldn't use an MOV across a connector. I was merely pointing out a way to give the switch an easier time and possibly your electronics too.
Incidentally, it's common practice in good-quality mains suppressors to put an MOV straight across the incoming mains. Of course it will have a working voltage of maybe 500 volts, but it gives you some idea of how robust they are. Such an MOV will prevent interference from your equipment getting out if it escapes the standard choke/capacitance setups used for suppression. They are magic even in extreme situations - one of my 'sidelines' (with a pal of mine) is Tesla coils, usually driven off a neon sign transformer (10kV) with a capacitor bank and a spark gap. Amazingly crude, very effective, and when properly tuned will produce continuous discharges a couple of feet long. They require serious filters, and MOVs are a godsend to make sure the things don't blank out East Enders for miles around....
As I mentioned, you really would not want to operate the switch under load. If you did, and the MOV did go short, take it that at 71p it will be easier and much cheaper to replace than assorted electronics. If you're frightened that your throttle might 'stick' then that's probably a good indication of where your emergency switch should go - not in the main supply leads at all. Also most e-bikes have cut outs built into the brake levers which over-ride everything - including a wide-open throttle.
Rog.
I wouldn't recommend a transorb (sometimes called a Superdiode) in this sort of application. They're a different animal entirely. Generally transorbs are good for protecting circuits running on lowish voltages, whereas MOVs are favoured for higher voltage, though there is some considerable overlap.
An MOV does its 'thing' over a wider window of voltage. In other words, it turns on progressively as the applied voltage rises, whereas a transorb goes from fully-off to fully-on over a much narrower voltage range. There are advantages to what an MOV does - it will absorb just enough power to kill off a dangerous transient, without taking all of it, which a Superdiode will often do. This contributes to the fact that they are really very robust.
As I said elsewhere, I wouldn't bother with either on a connector - I was just thinking of offering some protection to a switch and the electronics.
Rog.
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You don't need high voltages to get a spark, and you don't need inductance either (which would be more than cancelled out by the controller caps any way).
Try shorting out a battery and you will see what I mean!
You are right about the contact bounce. The low battery voltage is enough to cause the air to ionize and conduct across a very small gap which is then maintained by the high current as the gap increases.
It is exactly the same process as arc welding where you generally use a low voltage, high current supply and have to 'strike up' an arc.
BTW, what you describe above can and does happen in an inductive circuit, it's just that we don't have that case here.
It's not the 'short' that causes the spark - it's when the short is removed and you interrupt that HUGE current. When you do that you always get a massive voltage, simply because every circuit has inductance - even if it's only the path through the battery and the pair of pliers you so carelessly dropped across the terminals. Interrupting a small current through a tiny inductance will probably produce no spark at all, but when you have tens of amps flowing and you interrupt that, THEN you get a spark.
In this area, 'inductance' and 'capacitance' are two unrelated phenomena. They may be inter-related when it comes to an AC circuit, but here we're talking about a linear event - the caps charge up, and while they're charging (lots of amps) we break the circuit and get a spark. That's the end of the story. There is no 'lead' or 'lag' to consider, and although there may be oscillation when you break the circuit (which tends to keep the arc going) it's irrelevant and would needlessly complicate what's happening.
Welding is a good case in point - what you do is touch the welding rod to the work, a large current flows, and then you break the circuit immediately - at that point the arc 'strikes' because of the enormous voltage produced by interrupting the current. Once it starts - as long as the gap between the rod and the work is not too great - metal boils off and helps to keep things going, and you may well need much less than 100V to maintain the arc.
I do know of of rough 'n' ready welding kit where you just have a suitable current-limiting resistance (a few ohms, but a big 'un!) and string three or four truck batteries together. All you need then is some hefty cable, one large crocodile clip and the welding rod holder - and you're in business. It probably helps if you have some appropriate goggles handy too.
I repeat - ALL circuits are inductive! Even a couple of inches of wire is inductive. When you pass a large current and then interrupt it, this tiny inductance is what causes the spark. Being as non-technical as possible, an inductance does not like the current flowing through it to change, and will produce an appropriate voltage to resist any change you attempt to make - including opening a switch, which at least in theory causes an infinite current change in zero time - and that would produce an infinite voltage across any inductance at all. So, you get a spark, which limits the voltage (though perhaps not to a safe level) by allowing the current to die over a finite time period.
Your comment about the low battery voltage being enough to cause the air to ionize is not the case. As I have mentioned already, you need around 300V to start any sort of an arc in dry air. It's the circuit inductance producing the high voltage when the circuit is broken which causes the spark.
Rog.
I guess most people have nodded off by now on this curious debate
, but I thought I would add some further comments.Although not always reliable, wikipedia has this to say:
"For air at STP, the minimum sparkover voltage is around 380 volts.
While lower voltages will not generally jump a gap that is present before the voltage is applied, interrupting an existing current flow often produces a low voltage spark or arc. As the contacts are separated, a few small points of contact become the last to separate. The current becomes constricted to these small hot spots, causing them to become incandescent, so that they emit electrons (through thermionic emission). Even a small 9 V battery can spark noticeably by this mechanism in a darkened room. The ionized air and metal vapour (from the contacts) form plasma, which temporarily bridges the widening gap. If the power supply and load allow sufficient current to flow, a self-sustaining arc may form. Once formed, an arc may be extended to a significant length before breaking the circuit. Attempting to open an inductive circuit often forms an arc since the inductance provides a high voltage pulse whenever the current is interrupted."
I was focusing on the electric field required for breakdown and neglected the minimum voltage that you refer to (note that the voltage to maintain an arc can be very low). However, as I said, I think that inductance is a red herring in this case (pliers just don't have enough of it). Perhaps is will only get resolved by experimentation and doing the maths.
Nod off!, Never.I guess most people have nodded off by now on this curious debate
I just thought switches had become the new helmets.
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The question is do more switches make the rider more or less reckless?Nod off!, Never.
I just thought switches had become the new helmets.
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Well done, Flecc. I was getting decidedly bored with it all myself. Discussion ended, at least as far as I'm concerned.With the added safety of a switch, probably more wreck less.
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Rog.
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