Simple-Cheap Pre-charge Switch

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Simple-Cheap Pre-charge Switch

Postby DrkAngel » Tue Dec 22, 2015 7:33 am

Problem
Battery to controller connectors-switches can take considerable abuse from initial "connect".
Often typical is a spark or "snap".
To survive ... the connector, switch or contactor, must be heavier and more durable than is necessary for typical current during use.

Solution
Most common is the use of a Pre-charge resistor circuit.
This involves buffering the millisecond "spark" to a partial~multiple second "charge".
Keeping this circuit simple, reliable and inexpensive is the challenge!
Simple is easy:
Pre-charge Resistor.jpg
Pre-charge Resistor.jpg (22.2 KiB) Viewed 1601 times

Temp Pre-charge Resistor.jpg
Temp Pre-charge Resistor.jpg (28.43 KiB) Viewed 1601 times


Simple Pre-Charge - Switch
A simple, and cheap, on\off\on switch with the 2 positions shorted with a resistor makes an effective pre-charge circuit.
I position to charge, (couple seconds?) II to fully engage.
High V light bulb as replacement for resistor confirms pre-charge complete when bulb dims fully.
Proper resistor with LED would provide similar function. Might need Large resistor parallel with small resistor-LED.

PC Switch.jpg
PC Switch.jpg (58.09 KiB) Viewed 1598 times


Pictured switch is rated up to 15A in dual (pos and neg) disconnect and 30A as single disconnect (pos or neg).
Personally used at 25.9V and 33.3V w\35A controller on various eZips and survives hundreds of on off cycles before needing replacement.
Adding pre-charge should greatly prolong life even at higher Volts and Amps!
Also liable to prolong controller life. ... ?
Last edited by DrkAngel on Tue Dec 22, 2015 7:53 am, edited 1 time in total. View post history.
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Re: Simple-Cheap Pre-charge Switch

Postby Matt Gruber » Tue Dec 22, 2015 9:30 am

i do use pre-chg on my -9 scooter w/80 amp truck relay. first the ON switch pre charges, then the deadman GO switch triggers the relay. if the brush controller ever shorts, my thumb will come off the GO switch and kill the relay coil.
on my e-bike there is no need for pre charge as the stock controller powers off by itself, so no need to disconnect battery.
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Re: Simple-Cheap Pre-charge Switch

Postby DrkAngel » Tue Dec 22, 2015 11:58 pm

Dual Battery Pre-Charge Switch(es)

Switch on either of two separate batteries.
Press and hold appropriate (same side) momentary button before engaging switch.
2 handily positioned momentary contact switches

D switch1.jpg
D switch1.jpg (29.29 KiB) Viewed 1542 times


Dependent on resistor size, momentary switch can be of minimal Amp rating.

D Switch2.jpg
D Switch2.jpg (30.02 KiB) Viewed 1542 times
Switch(es)

Only 1 resistor necessary ...

Pre-charge resistor saves switch, connector, contactor, controller etc. life, prolonging solid, reliable, full power connection.

Oops! - confirm switch function.
Rocker switch press can enable opposite side contacts!!!


D Switch3.jpg
D Switch3.jpg (33.5 KiB) Viewed 1365 times
Last edited by DrkAngel on Fri Dec 25, 2015 8:07 am, edited 2 times in total. View post history.
A little learning is a dangerous thing;
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Simple-Cheap Pre-charge Switch

Postby scoobydrew » Wed Dec 23, 2015 5:32 pm

Hi, has anyone used any of the anti spark plugs from hobby King? Looking to delete some large awkward looking switches and resistors and was wondering if these would work.

Thank
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Re: Simple-Cheap Pre-charge Switch

Postby eee291 » Fri Dec 25, 2015 7:38 am

May I suggest a solution without using switches?


img20151225_133343.jpg
Precharger resistor soldered on one side and touching the other when connecting



img20151225_133558.jpg
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Re: Simple-Cheap Pre-charge Switch

Postby TheBeastie » Sat Jan 16, 2016 2:30 am

eee291 wrote:May I suggest a solution without using switches?


img20151225_133343.jpg



img20151225_133558.jpg

Thats a great idea, never thought of it that way, just a simple wire in front to get the juices flowing before the main connection, I think I will take this route on my next setup.. I was thinking of a simple precharge cable+plugs but I was fearing the idea that I would unplug the main cable one day and leave the little cable sucking away on the battery pack etc..
Not a problem with your setup..

Those HK connectors look interesting but they don't really describe how they work...
Last edited by TheBeastie on Sat Jan 16, 2016 2:31 am, edited 1 time in total. View post history.
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Re: Simple-Cheap Pre-charge Switch

Postby cwah » Sat Jan 16, 2016 3:14 am

I need that too
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz
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Re: Simple-Cheap Pre-charge Switch

Postby eee291 » Sat Jan 16, 2016 6:56 am

TheBeastie wrote:
Those HK connectors look interesting but they don't really describe how they work...


Describe? All you need to do is sodder one side with a female plug the other side with a male plug. They are called EC5 connectors, nothing that needs describing really only problem you can't put them connectors in their little plastic holders witch help you not to plug it in the wrong polarity. But if you look at this pic you can see how I bypassed this problem

img20160116_125446.jpg
Precharge resistor with sshunt in parallel
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Re: Simple-Cheap Pre-charge Switch

Postby macribs » Tue Feb 02, 2016 6:54 am

eee291 wrote:
TheBeastie wrote:
Those HK connectors look interesting but they don't really describe how they work...


Describe? All you need to do is sodder one side with a female plug the other side with a male plug. They are called EC5 connectors, nothing that needs describing really only problem you can't put them connectors in their little plastic holders witch help you not to plug it in the wrong polarity. But if you look at this pic you can see how I bypassed this problem

img20160116_125446.jpg



I like this a lot. Simple yet effective. But does it leave room for user errors? Should I pull that apart each time I park the bike? Before each charging? When do I pull it apart to stop current? And what happens if I do forget when I park the bike, charge it etc? Or disconnect only when long time parking, like going on holiday, parking bike for the two worst months of winter etc?

What specs of resistor should I look for when making pre charge switch? 22s10p 18650 if that matter.

Sorry if this seems lame, but I am reading up on all the topics I've been putting off "forever". And as I soon will start building the battery I should do the wiring first so all is good and ready when the battery is completed. Btw, that shunt is it only required if Cycle Analyst is used? Or is it a must for all controllers?
Last edited by macribs on Tue Feb 02, 2016 6:55 am, edited 1 time in total. View post history.
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Re: Simple-Cheap Pre-charge Switch

Postby eee291 » Tue Feb 02, 2016 9:17 am

I think you should look at the 2nd pic closely you can clearly see that the resistor isn't connected after I plug it in. And also you only need to use the resistor if you disconnect your pack or the BMS shut off because of LV.

As to the resistor question I think a 10watt resistor will do just fine or even a small light bulb like on the indicator of a moped or something, I'm sure Google has the answer.

In my case Kelly includes a 10w resistor with their controllers
Last edited by eee291 on Tue Feb 02, 2016 9:17 am, edited 1 time in total. View post history.
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Re: Simple-Cheap Pre-charge Switch

Postby yojimbo » Wed Feb 03, 2016 8:50 am

Moped bulbs will only be rated at 12v (13/14 in reality) so may have a short life when having 36v/48v or even more dumped through them, even if only momentarily, plus being made of glass they aren't terribly robust. My resistor choice is 100 ohms at 5w, zero sparking when touching it on, that will be wired to a 250v push switch across the main 30 amp switch contacts. I'll probably put a meter across the resistor so I can measure how long it takes to do the major charge part.
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Re: Simple-Cheap Pre-charge Switch

Postby DrkAngel » Wed Feb 03, 2016 8:59 am

Small 120V halogen bulb?
Will go dark when controller caps reach full.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Simple-Cheap Pre-charge Switch

Postby eee291 » Thu Feb 04, 2016 2:05 am

As I said a resistor works best. But you woupd just have to connect the bulb in series and it will light up only for a split second, but you have to keep it on for at least 10 seconds. BTW I did this for a whole year and it didn't break because the bulb is just another resistor.
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Re: Simple-Cheap Pre-charge Switch

Postby yojimbo » Thu Feb 04, 2016 10:21 am

Its a resistor that is designed to burn incandescently at the rated voltage, ie, close to melting point ;-) But yes I imagine they will last a good long while, the voltage drop across it would be very rapid.
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Re: Simple-Cheap Pre-charge Switch

Postby Ecyclist » Sat Sep 09, 2017 10:09 am

Thank you for the simplified presentation.
Don't expect from life to be easy and then it will be.
My builds:
viewtopic.php?f=3&t=90432#p1318056
viewtopic.php?f=28&t=82252
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Re: Simple-Cheap Pre-charge Switch

Postby Ecyclist » Thu Sep 21, 2017 2:42 pm

Hi guys,
I'm trying to figure out the best way to encase VESC and heatsink it at the same time. The problem I'm having is with capacitors. They are in my way. Would it be electrically and electronically sound to move capacitors a little away from the board and put the power switch between the board and capacitors? This way I could build a compact case for the VESC and house capacitors inside the battery case. Also, with that, I wouldn't have to worry about the pre-charge switch because capacitors would be connected to the battery pack in a semi-permanent way. :idea: What do you think :?:
Don't expect from life to be easy and then it will be.
My builds:
viewtopic.php?f=3&t=90432#p1318056
viewtopic.php?f=28&t=82252
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