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Argh! transistor that works with 70VDC?

shyronnie

Nov 1, 2011
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I have this L7812CV transistor but it only works with 30VDC max. It has got to work with 70 VDC.

Where can i get one? It has to open up a relay, that will short the ignition on my electric motorcycle.
- The copper contact plates in the ignition lock are fried due to the high voltage, so i need to do it another way.
A switch is not a good way, and it is hard to get switches that work with 70 VDC.

I think this transistor way is the best way.

By transistor i mean those small voltage regulators.
 

Resqueline

Jul 31, 2009
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Ignition systems are used with combustion engines, but you're saying you have an electric motorcycle, running on 70V (or maybe 72V?) batteries?
And you need a solid state "ignition" (on/off) switch? How much current will pass through this switch if I may ask?
 

shyronnie

Nov 1, 2011
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Lets call it a key lock instead. yes, 72 volts.

If i just connect a switch, there will be a current of 1.5 amps
 

Resqueline

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Ok, yes, that much DC voltage and current requires a quite fast switching action to avoid frying the contact elements. Not many key switches are up to that.
Is the switch in the positive wire, and would you be free to switch the negative wire instead, or is this the control input to the motor controller?
I was thinking something like the attached circuit may do what you need. The diode is there just for "safety" since I don't know if the load is entirely non-inductive.
The P-channel MOSFET can be replaced with a PNP Darlington, and if so the zener can be ditched.
If you can switch the negative line then N-transistors may be used instead.
 

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davelectronic

Dec 13, 2010
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Hi shyronnie.
Could you not use a relay activated by the ignition switch, a mains voltage type, some of those relays can go up to that i think in DC volts, the key ignition then would only operate the relay coil then, not 100% sure just a suggestion. :)
 

shyronnie

Nov 1, 2011
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No i think they are also too big. The fact that it can handle 250vac, does not mean that it can handle 70 VDC
 

davenn

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Sep 5, 2009
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No i think they are also too big. The fact that it can handle 250vac, does not mean that it can handle 70 VDC

Thats a bit of an illogical assumption. Switching 1.5A was mentioned up the page.
So 70V @ 1.5 A, thats pretty easy with a myriad of very small relays on the market.

And the activation voltage would also be 70V or 12V ?

I use a lot of 12V and 24V coil relays in gear I manufacture. They have a max DC V of 110V @ 10A their size is 22mm wide, 16mm long and 17mm high

Dave
 

shyronnie

Nov 1, 2011
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The only problem is, that the activation voltage is 70 VDC. It has to be!

And no it is not an illogical assumption?
AC cancels the spark, DC doesn't
 

davenn

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The only problem is, that the activation voltage is 70 VDC. It has to be!

for the very low current ratings of a relay coil .. say a 24V one anywhere~ 20 - 100mA depending on the make and model. you could probably get away with a 2 resistor voltage divider across the 70V to get a 24V drive :)


And no it is not an illogical assumption?
AC cancels the spark, DC doesn't

also not really a problem when you see all the HV DC relays out there that are available.
your assumption was based on a lack of info on available parts ;)

in the end you will do whatever you want to... all of us are just trying to give a few ideas of the possibilities :)

Dave
 
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