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2 or 4 amp EVSE

1965 Views 13 Replies 5 Participants Last post by  Solarsail

Is it possible to get an EVSE that is programmable down to 2 or 4 amps?

I have found this ( which goes down to 6 amps, but I would like to try even lower.

Thanks for any input,

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Current is simply set by a PWM signal

4 amps... It's not officially supported, if you did it anyway your charger would likely not handshake.

If you map your chargers power in behavior you might find its ramps slowly over 30 seconds to a minute, it would be much more complex but you could reset to 0 amps every 20 seconds or something so your charger doesn't draw over 4 amps

Ah well
Good Luck
Thanks a lot,

Based on that I did some googling of the handshaking and found: "After a connection is made, the EVSE provides the vehicle with information about its maximum available continuous current capacity by modulating the pulse width of the square wave between 100 and 800 μs. The relation is linear: 100 μs corresponds to 6 A; 800 μs corresponds to 48 A."

I guess this explains why a handshake for 4amps (i.e. 66 μs) wouldn't handshake as I guess the vehicle wouldn't know how to interpret it.


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Sorry to follow up again,

Am I therefore right in thinking that a 100 μs modulation on a 110v EVSE therefore leads to a 660w power draw?


What sort of battery pack and charger are you using to need such a low power draw--most folks are trying to find a way to charge faster?
Yes, it is an unusual direction,

I have 3 solar panels on the roof of my garage but no other power supply i. e. a max of 900w and am thinking of getting a hybrid (Golf GTE, and I don't drive daily), and so speculating whether with a inverter drawing from the panels and outputting 110v into an EVSE, I could keep the battery topped up for a few sunny hours a day?

I could use a buffer battery of course but was wondering if it would be possible without, as even now it wouldn't really be cost effective (but it would be mentally satisfying), but far worse if batteries, larger inverters etc need to be involved.

I think you are better off staying at 6A. This would be 660W except for all sorts of inefficiencies in the chain of power conversions. What I think you should do is add one or more solar panels. You can buy a 300W panel for as low as $100 (in quantity price).

Another hack, which I am sure a lot of people here will disagree with me, is to get to the HV terminals of the EV at the pack, tap into it, and with a CCCV charger do the trickle charge. Since you will always be charging and balancing the pack through the vehicle charger, balancing will not be critical on trickle charge, especially if you stop at 4.1V instead of 4.2V. If this will confuse the vehicle ECU, then just disconnect the 12V vehicle battery to put the ECU to sleep.
Hi Solarsail,

Are you aware of a charger that you let me trickle charge a Golf GTE pack via the HV connections? I think it is 96 cells at a nominal 3.6v - so would need to be outputting around 330v DC (and around 600w) with enough intelligence to disconnect when the voltage went higher? I didn't think this kind of thing existed, but maybe I am missing a trick? Could a Brusa or similar be set to run with a very low wattage?


If Brusa makes a 400V CCCV charger, then I believe the current is selectible. But not sure if it will go as low as 4A as they are designed for fast charging I would think. And it will be expensive.

One cheap idea is to string 6x 60V (or 5x 72V) isolated 300W DC switching supplies in series and then tied to one 50V CCCV charger. Each can cost as little as $30. This may not give you the necessary stability, but on paper it should do the job. The 50V charger will be set at 96*4.1-6*60 = 33.6V and 2A or 4A. If the result is good and the set up is stable, then the charger can be set to charge at 38.4V.

Another idea is that the EV internal charger is designed to draw less current when it senses the battery to be almost full. Maybe you can trick it to believe the battery is almost full causing it to charge at a lower rate.

Put a resistor in series between the vehicle charger and the pack. For example a 5 ohm high watt resistor. This may cause the charger to think that the pack is getting full and start drawing less current. As it draws less current, the voltage differential across the resistor drops. So the pack will get charged to its maximum, but at a slower rate. The value of this resistor depends on the state of charge of the battery. So you will need to reduce the value as the pack voltage increases. You could use an incandescent light bulb as the resistance drops as the voltage across the lamp decreases.
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BS meter is going off here ^

Hey Solar where are you coming up with all your hair-brained ideas? Have you tried any of these and have experience? Is any of this based upon any test data? Did you even read the OP to know what the discussion is about?

What good is a 50V charger when he has a 400V pack?

How do you suppose anyone could insert a 5 Ohm resistor between the cars on-board charger and the positive terminal of the pack? Or insert an incandescent lamp? Did you even consider or think about that before posting such nonsense?

Test your crazy ideas at home on your own stuff, then post the results.
Whoa - cool down Kenny boy. If you have forgotten, this place is called DIY - meaning if necessary you try to be creative and may experiment, and if there is no obvious solution, then you may try things outside of the book. If you want to cling to your nanny safe space, that is your option, but no need to be rude. It has not been written in the Bible that it is a grave sin to work on the HV line. Anyone with some knowledge of electrical engineering would know how to do that.

That is exactly what I am doing on my Leaf and there are write-ups on the net about that.

"Have you tried any of these and have experience?" -- do I have to? I have made it clear that these are ideas, and not true and tested courses of action.

"Is any of this based upon any test data?" -- by definition there are no experimental data on ideas and methods not generally tried. You don't go by the data, you go by the model.

"What good is a 50V charger when he has a 400V pack?" -- did you even bother to read and understand what I wrote? I said string six 60V DC CV power supplies with one CCCV charger. Read again.

There is a contactor, switch or connector between the pack and the hybrid power circuit. You open that contactor, switch or connector and insert a resistor. When you want to drive, you remove the resistor and close what has been opened, or short the resistor. Any engineer can tell you how to do that. And no, it is not taboo or evil to work on the HV line.
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Put a resistor in series between the vehicle charger and the pack.
That actually is hairbrained :) OP has limited charge power available and you are suggesting turning half of that into heat.

OP. 6 amps is the least specified by j1772 EVSE AFIK, but your charger can draw as little as you like, the EVSE won't care as long as you don't exceed the 6 amps or whatever it is advertising in the pwm duty cycle.
The idea with the resistor is that it will make the pack appear at a higher voltage to the charger. That will cause the charger to hit the CV ceiling, which will cause it to draw less current from the supply. If done right, it could make it drop demand from 6A to 2A. 2A at 110V is 0.5A at 400V. The loss with a 5 ohm resistor will be only 1.25W. The supply is about 200W.

But question is can it be done for the whole range of pack SoC. Will probably need a mosfet operating in its linear region with a bunch of control electronics, or a digital controller. It may not be pretty or reliable. A better solution may be to get into the vehicle charger and hack the CC circuit to reduce the current draw. All CC circuits have a divider somewhere that can be hacked. This would be a clean way of doing it, but would require access to the vehicle charger schematics and the charger board, and willingness to hack vehicle electronics.

I think the fastest, cheapest and easiest solutions are triple solar panels to 900W output (not very useful on cloudy days or before 10AM and after 4PM), or tap into HV and use the 6x60V+50V hack to trickle charge.
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You can put 4 of these in series to get 400V.

I have one of these and tested it, and unfortunately they are not isolated.

Or four of the below, and one of the above in series. I have a step-up DC-DC converter similar to this, and it appears to be isolated (open circuit between negative in and negative out), but am not sure, and have not tested it. Probably not isolated.

Run them at a fixed 24 volts to get better stability.
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