## Need a circuit designed to limit charge to XX amps max

TonyWilliams
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### Need a circuit designed to limit charge to XX amps max

I need a circuit designed that will limit the maximum EVSE pilot signal "duty cycle / pulse wave modulation" to the following:

1) EVSE pilot signal > than XX duty cycle, output XX pulse wave modulation (PWM) only
2) EVSE pilot signal <= to XX duty cycle, let the EVSE's PWM pass through unchanged

This device would be placed between the EVSE plug pilot signal pin and the cars pilot signal pin. That signal is a 1kHz 12/-12 volt square wave with the following duty cycle:

10% - 96% = 6 amps - 80 amps
>96% = Error

One simple option might be:

Duty cycle from EVSE is > XX, then PWM = 96%. This wouldn't work with duty cycles greater than XX% to continue operating at XX or lower, but would merely not work over XX.

I want to be able to limit to XX%, not stop above XX%.

http://www.teslamotorsclub.com/showthre ... post445524

Last edited by TonyWilliams on Fri Sep 27, 2013 9:36 am, edited 2 times in total.

donald
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### Re: Need a circuit designed to limit charge to XX amps max

It might depend on how accurate you want to be.

If I understand your requirement, then perhaps you might consider a 555 based monostable that triggers on the trailing edge of the last pulse, and which then enables a triac that carries the through-signal [only] after a set time. If the set time is shorter than the interval between pulses then it will have no effect on the through signal [e.g., a set time of <40us would have no effect on a duty cycle <96%]. If the set time was, say, 300us then it would limit the duty cycle to 70%, yet have no effect on, say, a 50% duty cycle signal (and would also carry + and - signals, irrespectively).

TonyWilliams
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### Re: Need a circuit designed to limit charge to XX amps max

donald wrote:It might depend on how accurate you want to be.

If I understand your requirement, then perhaps you might consider a 555 based monostable that triggers on the trailing edge of the last pulse, and which then enables a triac that carries the through-signal [only] after a set time. If the set time is shorter than the interval between pulses then it will have no effect on the through signal [e.g., a set time of <40us would have no effect on a duty cycle <96%]. If the set time was, say, 300us then it would limit the duty cycle to 70%, yet have no effect on, say, a 50% duty cycle signal (and would also carry + and - signals, irrespectively).

All good points... thanks.

Tony

essaunders
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Location: southern NH

### Re: Need a circuit designed to limit charge to XX amps max

how are we powering this?

simple is best, but we might be back to having to deal with a 120 to 240v capable powersupply - once we have all that, it's probably just back to the Open EVSE guts with some extra logic.

If we can do it on just the power in the pilot then a super simple analog would be OK. -- not to overthink this -we're just trying to keep a tesla-inside car from killing a 30A max J1772 extension by mistake, right?

TonyWilliams
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### Re: Need a circuit designed to limit charge to XX amps max

essaunders wrote:how are we powering this?

simple is best, but we might be back to having to deal with a 120 to 240v capable powersupply - once we have all that, it's probably just back to the Open EVSE guts with some extra logic.

If we can do it on just the power in the pilot then a super simple analog would be OK. -- not to overthink this -we're just trying to keep a tesla-inside car from killing a 30A max J1772 extension by mistake, right?

Yep, that's the goal. I want a nice light, simple, and "cheap" J1772 extension cord, and it's sorta dumb to make it 80 amp capable when almost all the public charge stations are 30 amps.

But, since some EVSEs are indeed 70 or 80 amps, the 30 amp cord needs smart protection from a Tesla driver who can suck down 80 amps.

The power has to come from the 100-250 volt power going through the cable, since I have no idea how much "power" is actually in the pilot signal. So, for at least a millisecond, there will be a pilot signal over 30 amps until it can be changed to 30 amps or less.

We absolutely don't need all the stuff in the OpenEVSE; no relays, no GCFI, no diode check, no stuck relay logic, et al.

chris1howell
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### Re: Need a circuit designed to limit charge to XX amps max

Hi Tony,

You should check out "Hydra" on the OpenEVSE site. It was designed by nslayer to split a J1772 into 2 the and share the source pilot. It sounds like you want Hydra with a single output.

Hydra is losely based on OpenEVSE. I bet it would be perfect for your need with a few code changes.
2011 LEAF: Red SL #04122
2012 Tesla Model S #01530
EVSE: OpenEVSE, 40A L1/L2 -- http://www.openevse.com
PV System: 28 x 210W -> 5.8 kW DC

OpenEVSE Store: http://store.openevse.com

TonyWilliams
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### Re: Need a circuit designed to limit charge to XX amps max

chris1howell wrote:Hi Tony,

You should check out "Hydra" on the OpenEVSE site. It was designed by nslayer to split a J1772 into 2 the and share the source pilot. It sounds like you want Hydra with a single output.

Hydra is losely based on OpenEVSE. I bet it would be perfect for your need with a few code changes.

Yes, I was thinking about that. I was hoping for something far, far simpler for this one job.

Thanks,

Tony

pchilds
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### Re: Need a circuit designed to limit charge to XX amps max

Just match the cable to the vehicle.
2011 LEAF, gone,
2012 RAV4 EV,
2015 Model S 85D,
Solar PV 5.25 kW system.

TonyWilliams
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Location: San Diego
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### Re: Need a circuit designed to limit charge to XX amps max

pchilds wrote:Just match the cable to the vehicle.

Of course, except... in the mass market, somebody would eventually have a 15 or 30 amp cord and try and pull 80 amps through it.

johnrhansen
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### Re: Need a circuit designed to limit charge to XX amps max

How about a 30 amp fuse?
2013 S model with quick charge package.
AV 30 amp level 2 EVSE, Bosch PowerMax 30 Amp EVSE, EVSE upgraded EVSE.