Power Switch

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LewTwo   100 kW

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Power Switch

Post by LewTwo » Nov 16 2016 5:19pm

I have a Golden Motor Smart Pie front hub motor system and a Luna Cycle 52 Volt Shark battery pack. I am moving the GM system from one bike to another and upgrading from the GM 36 Volt battery to the Luna Cycle 52 Volt battery. The GM battery Key Lock includes a feature to turn the battery ON or OFF. The Luna Cycle Sharp key lock only locks the battery to the mount. So I now have a system configuration in which the only way to turn off the power is to remove the battery. I am looking for a way better alternative.

The most straightforward solution is to wire a switch in the power line but we are talking about 60 Volts and 20 to 30 Amps (somewhat overstated). That would be a big honking switch. I was considering a solid state relay. Anyone ever try this approach? Other comments or suggestions?
FOTEK SSR-25DD(400).jpg
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Re: Power Switch

Post by Hillhater » Nov 16 2016 7:19pm

well, i suspect the volt drop across that at 60v, 30 A ( 1.8kW) might be a little disappointing !
Love to see a test though.
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Re: Power Switch

Post by LewTwo » Nov 16 2016 11:19pm

Apparently they have a bit of a problem with counterfeit and clone versions. Here is a YouTube video of one taken apart. Interesting to note that the Triac used is HALF the rated current of the relay. Of course this is a zero crossing AC design ... I have not been able to find much information available on the DC load versions.
https://www.youtube.com/watch?v=DxEhxjvifyY

What disappoints me is that the BMS has a set of Mosfets in it than can shut down the power if the pack goes over temperature or current draw is too high. Does not seem like it would have taken too much effort to include provision for an ON-OFF switch as well.
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Re: Power Switch

Post by amberwolf » Nov 17 2016 1:28am

You could add one easy enough by finding the FET gate pin.

To use a switch to turn on the FETs, you can add a resistor in series with a switch that goes to the same voltage on the BMS that the cell-monitoring-electronics uses to drive the gate.

To use a switch to turn off the FETs, either add switch that grounds the FET gate, or add a switch in series with the gate (you'd have to cut a trace somewhere between gate and the BMS control circuit that drives it) and add a resistor from gate to ground, so that opening the switch grounds the gate and turns off the FETs.

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Re: Power Switch

Post by jpgey » Nov 17 2016 2:55am

I tried some of these SSR and they burn if the inrush current is to high. That mean you still have to deal with a pre-charge resistor before switching the main power with the SSR.
As I wanted to use only one switch to power the bike I had to connect like this:
IMG_20161117_084613.jpg
IMG_20161117_084613.jpg (90.71 KiB) Viewed 202 times
The main switch connect the pre-charge resistor and activate the SSR after after a few seconds ( with the small resistor and the capacitor).
When the SSR is activated it connect directly the battery + with the controller +
When the main switch is off the SSR is powered OFF and cut the power to the controller
With this setup there is only one small switch and when it's Off it's really Off, no current to the controller.

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Re: Power Switch

Post by jpgey » Nov 17 2016 2:57am

Also, don't forget to add a heatsink on the SSR as it may be hot with high power bike

Example:
https://endless-sphere.com/forums/viewt ... 8#p1120590

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Re: Power Switch

Post by LewTwo » Nov 17 2016 3:43am

jpgey wrote:Also, don't forget to add a heatsink on the SSR as it may be hot with high power bike

Example:
https://endless-sphere.com/forums/viewt ... 8#p1120590
That is a big heat sink! Image
I was thinking that just clamping it to the frame might be adequate but if it is going to produce that much heat then it is wasting so much power that the idea is a non-starter.
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Re: Power Switch

Post by LewTwo » Nov 17 2016 5:09am

amberwolf wrote:You could add one easy enough by finding the FET gate pin.

To use a switch to turn on the FETs, you can add a resistor in series with a switch that goes to the same voltage on the BMS that the cell-monitoring-electronics uses to drive the gate.

To use a switch to turn off the FETs, either add switch that grounds the FET gate, or add a switch in series with the gate (you'd have to cut a trace somewhere between gate and the BMS control circuit that drives it) and add a resistor from gate to ground, so that opening the switch grounds the gate and turns off the FETs.
Bare with me ... electronics is not my strong suit.

The Mosfet in the upper right corner goes to the charge connection. It is a RU8590R.

The mosfets are RU8590R and there are six of them. The 'GATE' pins are the ones on the left in this picture. That big blue wire is the negative side of the 58 volts power going out. Between it and the gate pin I have a 11.65 volts with the negative side on the output wire. The source and drain pins are at the same voltage level as the output wire. Between the gate and either the source or drain pin I have 11.65 volts again. That grid just above the right hand mosfet is also at the same level as the as the negative output. All that tells me that the BMS has the six mosfets paralleled across the negative output line.

If I am reading all this correctly then what I need to do is:
... unsolder or cut the gate pins (this would effectively switch OFF all the mosfets).
,,, connect the gate pins together with a wire (it could be something like 18-20 AWG because the gate does not use much power)
... add a switch between the wire and one of gate pin pads (each of those pads has a small surface mount 1/8 watt resistor next to it... the label reads 101).

Edit: The trace on the back with two hole under the left mosfet is the one that feeds the gates. It has a corresponding trace along the edge of the top of the board that the resistors are connected to.

Image
Luna BMS back.JPG
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Re: Power Switch

Post by jpgey » Nov 17 2016 9:46am

LewTwo wrote:
jpgey wrote:Also, don't forget to add a heatsink on the SSR as it may be hot with high power bike

Example:
https://endless-sphere.com/forums/viewt ... 8#p1120590
That is a big heat sink!
I was thinking that just clamping it to the frame might be adequate but if it is going to produce that much heat then it is wasting so much power that the idea is a non-starter.
Yes it is overkill, but it was easier for me to clamp this heatsink. Also this is for a 7000W setup.

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Re: Power Switch

Post by amberwolf » Nov 17 2016 2:47pm

LewTwo wrote:The Mosfet in the upper right corner goes to the charge connection. It is a RU8590R.
Yes, this one you don't have to mess with as long as your charge and discharge connections are separate.

That big blue wire is the negative side of the 58 volts power going out. Between it and the gate pin I have a 11.65 volts with the negative side on the output wire.
Sounds normal; there will be a 12v source somewhere on the BMS for the gate drive, probably sourced at the 3rd cell's positive if it's not LiFePO4, and the fourth cell's positive if it is LiFePO4. It could have a 3-pin (or other, smarter) 12v regulator (usually marked 7812 or similar) that produces this voltage instead, but probably not--this is why the bottom few cells can get killed or unbalanced vs the rest of them on packs left alone a long time without being used.
The source and drain pins are at the same voltage level as the output wire.
also normal; there will be a voltage across them when the bms is "off", though any current draw should collapse this.


If I am reading all this correctly then what I need to do is:
... unsolder or cut the gate pins (this would effectively switch OFF all the mosfets).
,,, connect the gate pins together with a wire (it could be something like 18-20 AWG because the gate does not use much power)
... add a switch between the wire and one of gate pin pads (each of those pads has a small surface mount 1/8 watt resistor next to it... the label reads 101).
The unsoldering gate pins is easy, and reversible enough. I'd go with the other method below, though.
Those resistors are 100ohm, IIRC (10 + 1 zero on the end, in ohms. 102 would be 10 + 2 zeros, etc).
Edit: The trace on the back with two hole under the left mosfet is the one that feeds the gates. It has a corresponding trace along the edge of the top of the board that the resistors are connected to.
This is the "easiest" place to put the switch--just cut the trace somewhere, and put the switch across it.

The only thing you might have to do, if it's not already built in there somewhere, is a resistor to ground (battery negative) (like 10kohm or so, maybe higher), as a pull-down to prevent the gate from "drifting" to a partially-on state. The board may already be wired like this, or the FETs may be of a type that this won't be much of a problem, so you might not have to worry about it at all.


Anyway, either method is pretty simple to test, and if it doesn't do what you want, simple to undo.

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Re: Power Switch

Post by LewTwo » Nov 17 2016 4:10pm

amberwolf wrote:
Edit: The trace on the back with two hole under the left mosfet is the one that feeds the gates. It has a corresponding trace along the edge of the top of the board that the resistors are connected to.
This is the "easiest" place to put the switch--just cut the trace somewhere, and put the switch across it.

The only thing you might have to do, if it's not already built in there somewhere, is a resistor to ground (battery negative) (like 10kohm or so, maybe higher), as a pull-down to prevent the gate from "drifting" to a partially-on state. The board may already be wired like this, or the FETs may be of a type that this won't be much of a problem, so you might not have to worry about it at all.

Anyway, either method is pretty simple to test, and if it doesn't do what you want, simple to undo.
I leaning toward putting a switch in place of the trace. I think that I can use the ends of the trace as surface solder pads and connect two small wires to run to a key switch. The 100 ohm (thank you for the explanation) resisters will still be in series with the gates.
Luna BMS back trace.JPG
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Re: Power Switch

Post by LewTwo » Nov 17 2016 10:44pm

jpgey wrote:Yes it is overkill, but it was easier for me to clamp this heatsink. Also this is for a 7000W setup.
Ah ... that makes a bit of a difference. I am looking at less than 1000 watts (17 Amps) max draw. I think I prefer modifying the BMS if I can and the more I think about it, I am leaning toward replacing that trace on the back with a switch.

However it seems very few BMS's include provisions for a switch. I am interested enough that I ordered two of the cheapest DC SSR units off EBAY .... delivery via a slow boat from china. I plan to destroy one of them to see what is inside. I am guessing that the circuit would be similar but maybe not exactly the same as the AC units. I took the liberty of redoing your schematic and I have four question on four different approaches. I am going to post four responses so people can comment on each one if they desire.

Looking at your schematic it looks like a six volt voltage divider circuit to me (I did say electronics is not my strong suit). However it seems to me that the one of the resistors is an order of magnitude too large and one would wind up with only 0.6 volts DC for the input of the SSR. I think one of those resisters needs to be 500 ohms.
wire diagram one(799).jpg
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Re: Power Switch

Post by LewTwo » Nov 17 2016 10:47pm

Next question is if one only wants avoid a big spark when the battery is plugged in then is this the correct wiring diagram?
obviously wrong
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Re: Power Switch

Post by LewTwo » Nov 17 2016 10:56pm

I was thinking of using a low power 6 Volt buck step down unit to drive the low side of the SSR (I need 5 VDC for lights anyway). In this case I do not believe that I would need the pre-charge circuit as the minimal load from the step down converter is going to be the only load seen by the battery when it is plugged in (assuming the switch is open). Am I missing something obvious?
wire diagram three(799).jpg
wire diagram three(799).jpg (37.01 KiB) Viewed 2046 times
OK ... I cheated when it came to drawing the DC-DC Converter.
Input Voltage : 4.5-56V
Output voltage: 3-35V
Minimum voltage difference: 1.5V
Output current: rated current is 2A
Output power: 15W(Max)

Reference: http://www.ebay.com/itm/152250836072

Update: seem that there are some counterfeit problems with these as well .... https://www.youtube.com/watch?v=JLwJb4MVbls&t=554s
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Re: Power Switch

Post by LewTwo » Nov 17 2016 11:37pm

OK, I have not got a illustration for this one because I have yet to fully understand the problem/solution well enough.

In watching the video I noted that the principle component used in the SSR was a Triac BTA12-600B. First of all this device is only rated for 12 Amps and is used in a SSR rated for 25 Amps. Now I understand when something is 'down rated' for some reason but I tend to get suspicious when something is 'up-rated' (just my cynical nature). Of course this was for an AC load and we do not have AC batteries on our bikes. That is the reason that I ordered two of the DC-DC SSRs. I plan to tear one apart to see what is actually inside. I will post that information to this thread when I receive the units.

That being said I suspect there are several features in the AC SSR (and possibly in the DC SSR) that are not really need in this application: zero crossing switching, opto isolation, LED indicator, low voltage regulation, etc. I suspect that if one used a step-down module that the only things really needed for the 'soft' battery switch is the switch, proper semi-conductor (SCR ?) and perhaps a couple of resistors and a capacitor. This might also be advantageous in fitting the 'switch' into a battery pack such as the Shark that has a built in heatsink ... but not nearly enough space to fit one of the SSR units.

See this thread: https://endless-sphere.com/forums/viewt ... =3&t=40142

Lastly I am attaching a compressed archive copy of the TWO DWG files and higher resolution PNG files for the previous diagrams to this message for anyone that that might want access to them.
wire diagrams.zip
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Last edited by LewTwo on Nov 18 2016 9:00pm, edited 2 times in total.
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Re: Power Switch

Post by amberwolf » Nov 18 2016 2:32am

LewTwo wrote:Next question is if one only wants avoid a big spark when the battery is plugged in then is this the correct wiring diagram?
wire diagram two(799).jpg
I don't have a diagram, but there ought to be quite a few under "precharge" or "anti-spark" or similar, here on ES or on google, possibly even on our wiki if anyone got an article up there. ;)

But before you go looking, basically you split either the positive or the negative wires from the battery and controller into two where they meet, so you now have three connectors between batt and contr. One of the split wires doesnt' ahve to be very big, as it doesnt' supply much current; it's going to be used for the precharge.

This wire is connected, battery to controller, and then the main wires of opposite polarity are connected (or leave those main wires always connected). After perhaps 30 seconds you could then connect the other main wire pair together, and there would be little or no spark as the caps are now mostly charged.

On that wire, on either batteyr or controller end, doesnt matter which, you insert a resistor of 1w to 5w size, depending on how much current it needs to handle, and calculate it's resistance based on your pack voltage vs the capacitor size in the controller to charge the caps to 70-90% in about 30 seconds.

I don't remember the actual calculation, but the resistor is usually some fairly low value, in the hundreds of ohms, to perhaps low kohms, IIRC.

The idea is just to slow down the charging of the controller's caps.


But you dont' want to add any other caps in there; it's just more capacitance that needs tob e charged up and increases the load on the precharge resistor. ;)

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Re: Power Switch

Post by izeman » Nov 18 2016 7:40am

amberwolf wrote:I don't have a diagram, but there ought to be quite a few under "precharge" or "anti-spark" or similar, here on ES or on google, possibly even on our wiki if anyone got an article up there. ;)
+1. search for "inrush limiter" "anti spark" or "precharge" and you WILL find more infomation than you can take :)
there are a lot of possible ways to do it right and trouble free, plug & play.

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Re: Power Switch

Post by LewTwo » Nov 18 2016 9:10pm

amberwolf wrote:... But before you go looking, basically you split either the positive or the negative wires from the battery and controller into two where they meet, so you now have three connectors between batt and contr. One of the split wires doesn't have to be very big, as it doesn't supply much current; it's going to be used for the precharge.....
That works for loose packs and cables but does not lend itself to a pack that has a fixed connector. :cry:
izeman wrote: search for "inrush limiter" "anti spark" or "precharge" and you WILL find more information than you can take :)
there are a lot of possible ways to do it right and trouble free, plug & play.
Thank you 'inrush' led me to the 2012 thread but alas it is 23 pages long. Going to take me a few days to work my way through it. :)

Reference: https://endless-sphere.com/forums/viewt ... =3&t=40142

So I found the 'equivalent' DC SSR from Crydom = D1D20
Dang, these suckers are expensive ... about $75 a pop.
Somewhat more than the $3.50 Chinese Fotek units found on Ebay.

Digikey: http://www.digikey.com/product-detail/e ... 38-ND/7525
PDF: http://www.crydom.com/en/products/catalog/1_dc.pdf
DC-SSR-X.png
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Re: Power Switch

Post by LewTwo » Nov 26 2016 9:03am

Before I amke any modifications to the BMS board I wanted to get a spare board in case I screwed it up.
Luna Cycles replied that they were available only for repairs. I am not a happy puppy 'bout that. :cry: :evil: :twisted:

I did run across another alternative ... DC Circuit breakers.
Available on EBAY branded as "MidNite Solar" for $20 each
These are only 13mm thick (1/2 inch)
Image

Northern Arizona Wind and Solar also has 'Panel Mount' circuit breakers rated for 150 Volts:
They are 3/4 inches thick
https://www.solar-electric.com/pamodccibr.html
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Re: Power Switch

Post by amberwolf » Nov 26 2016 2:46pm

Personally, if I had a BMS on my pack, and I wanted to avoid sparks, or have a power switch, I would just use the switch on the BMS FET gate(s) to do it. :)


Because I don't have a BMS on my EIG pack, which is the main pack I use on my stuff, I have a circuit breaker used as a switch on CrazyBike2, though it's not quite the right one--it's off a powerchair setup, and while it's DC, I think it is 24v 100A; even though it's not actualy rated for high enough voltage, it has successfully broken the circuit automatically a few times, but unless I'm messing with things I shouldn't it hasn't really needed to. :oops:

It's been cycled thousands of times, though (lost track a long time ago), and still works, so it's way better than some big switches I've tried out that became intermittent or failed shorted or open in just a few dozen or hundred cycles.


I have another similar one but with three paralleled linked breakers that will probably go on SB Cruiser at some point, but presently I just use the SB50 andersons for connect/disconnect, and they handle the sparking well enough without welding together (unlike the pp45s that I've welded together a few times before I went to SB50s for main battery connectors).

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Re: Power Switch

Post by atarijedi » Nov 26 2016 10:17pm

Gigavac contactors. They have really low power coil versions (only uses 12V/1W to power the coil), that could be setup to switch the battery, costs like $160 though. I've been pondering this, but that's a lot just for a relay for an eBike.

I've been thinking of getting one to control the battery, and then using the key switch to power the coil, and a momentary switch to temporarily power the DC/DC converter, so I can switch the relay on. It's gonna be like starting an old airplane, with a really big let down, lol.

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Re: Power Switch

Post by LewTwo » Nov 27 2016 2:59pm

amberwolf wrote:Personally, if I had a BMS on my pack, and I wanted to avoid sparks, or have a power switch, I would just use the switch on the BMS FET gate(s) to do it. :) ...
I like that idea. I have collected all the bits to do including a key switch. However I want a plan "B" in case I screw up or something goes wrong (that could never happen ...). That means having a source for another 14S BMS board. That is something I have to research .... Yo Google ... here I come ... again.
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Re: Power Switch

Post by amberwolf » Nov 27 2016 3:35pm

Yeah, I can understand that.

I'm working out an upgrade path for my SB Cruiser trike, based on some stuff being sent to me, but it might require changing the whole system voltage well above the capabilities of any of the stuff I just have laying around, so if I go that way I would need to get spares of anything critical to keep around just in case of failures I can't easily and quickly fix. :/



Regarding sources; there's a number of threads talking about a "BestTech" BMS that seems to do ok for people (though there are failures reported).

I don't know what kind is in my EM3EV A123 pack (that I got used) but it seems to be still working well enough. At some point it will get a switch built into it to do what we were talking about above. Not the right type for your cells but I'd bet they have or can get the kind you do need---shipping might be a killer though (or wait time, or both).

I know people talk about the ones BMSBattery has, but I don't trust anything from them; too many people either never get anything, or get something different than what they ordered, or stuff that doesnt' work (or not as advertised) that they have a terrible time getting repaired or replaced, if they even can. (of course, lots of other people have no issues whatsoever with them, even after many orders...but enough problems have been reported I still don't feel any possibility of trust).

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Adamlivi   10 mW

10 mW
Posts: 26
Joined: Nov 26 2016 2:52pm
Location: Norcross, Georgia

Re: Power Switch

Post by Adamlivi » Jan 07 2017 9:26pm

I just ordered and received one of these for my 52v 17 ah pack going on my tangent ascent build......seems quality.
http://diyelectricskateboard.com/diy-el ... er-switch/

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