DIY Electric Car Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
Hi guys, I wired up a J1772 plug and it’s only drawing 0.6KW from the chargepoint station.

The charger i’m using has been used in the past, and I’ve measured ~2.2KW of power draw so I’m stumped.

123539



The only thing I’ve done differently was using a 1N4004 diode instead of a 1N4003, and using 3 resistors in parallel (1K, 10K, 10K) which measured around 829 ohms. Aside from that, i’m not sure what I’m doing wrong. I’ve measured the J1772 output and it measured 205VAC so it’s delivering power. The only problem is the current being severely limited for some reason. Has anyone run into this issue before?
 

·
Registered
Joined
·
577 Posts
3 resistors in parallel in place of which resistor? In place of the 2.7k and you will have problems. You have no business trying to make 877 ohms on your side of the connector, by the way (I think that's what you're trying to do).

Resistors are $0.05 apiece. Why on earth wouldn't you follow the application note's exact recommended values?
 

·
Registered
Joined
·
209 Posts
I don't believe any of that resistor/diode business has any impact on the power being delivered. If I'm not mistaken, J1772 will communicate the amperage available, but has no ability to throttle it. So I think your charger isn't pulling all the juice it should for some reason.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #4 ·
3 resistors in parallel in place of which resistor? In place of the 2.7k and you will have problems. You have no business trying to make 877 ohms on your side of the connector, by the way (I think that's what you're trying to do).

Resistors are $0.05 apiece. Why on earth wouldn't you follow the application note's exact recommended values?
According to that diagram, they were shooting for 877 ohms. All I had laying around were 1K and 10K resistors, i’ll probably go out and buy some more, but what’s the difference between my setup and theirs? I don’t have a “S1” switch so my resistor values are pretty much the same as theirs (82x vs 87x)
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #5 ·
I don't believe any of that resistor/diode business has any impact on the power being delivered. If I'm not mistaken, J1772 will communicate the amperage available, but has no ability to throttle it. So I think your charger isn't pulling all the juice it should for some reason.
That’s so weird, I tried it on both my charger and my friend’s charger. 220V input, 72V 30A output. We both tested ours when we first got it, and it outputted around 25-26A to the battery. Now it’s only outputting around 6-8A. Maybe I’ll try it on my bike and see if it changes anything
 

·
Registered
Joined
·
577 Posts
Looking at it once again....

The resistor formula is wrong. R1 should be R3

Your two 10k's in parallel in place of the 2.7k is 5k, giving you 10V for connected, not ready. This then issues the ready signal when the switch is closed to which your 1k is connected, which in your case will be 5.4V.

If you go straight to ready, without the not ready state, like you would with just three resistors in parallel and no switch, the charger might get upset. Might.
 

·
Registered
Joined
·
209 Posts
According to that diagram, they were shooting for 877 ohms. All I had laying around were 1K and 10K resistors, i’ll probably go out and buy some more, but what’s the difference between my setup and theirs? I don’t have a “S1” switch so my resistor values are pretty much the same as theirs (82x vs 87x)
By the spec, 2.7K is the "vehicle detected", and then when charger activates it should go to 882R. But in your case the charger is drawing power, so I conclude that the charging station was happy enough with the resistors to activate the output.

Do you have a way to check if both L1 and L2 are energized ? I'm wondering if this charger can just pull 120VAC from either of the L1 or L2 and against the neutral.
 

·
Registered
Joined
·
209 Posts
If you go straight to ready, without the not ready state, like you would with just three resistors in parallel and no switch, the charger might get upset. Might.
You mean charging station ? Because I don't see why charger would care - it's no different than plugging it into a dryer outlet :)
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #9 ·
Update: So I have a J1772 charger adapter that I bought from ebay, and my friend decided to make one from scratch. He tried using his charger + my charger, with his J1772 and my J1772. All 4 combinations resulted in only a 600-800W supply when charging his bike.

I just went out 5 minutes ago and tried my J1772 adapter + charger on my personal bike, and it successfully charged it at 2.2KW.

Seems like something's wrong with his battery if that's the case, but we will do more diagnosing tomorrow.

My J1772 has no switch either, it has 2 resistors in parallel(R2 and R3 in the picture) totaling around 870-880 ohms. When we wired his up, I only had 1K and 10K ohm resistors laying around, so I decided to try to get the resistance value as close to mine as possible, and got ~820 ohms. I'm going to be trying his adapter tomorrow on my bike and see if it charges at the current it's supposed to charge at.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #11 ·
Okay we did more testing, and both J1772 and chargers are working fine today. Our theory is the charger having some issue determining the SOC of the battery, and was throttling the current when it's not supposed to. When it was only drawing 6A yesterday, the battery was at 72V (20S li ion). However today when it was at 78V, it charged at 2.2kw without any issues. We're suspecting that the charger isn't charging properly when the battery voltage is low, so we'll be draining the battery down and seeing if we can replicate the issue.

Today we tried plugging in both our chargers at the same time in parallel, but it only drew around 3.1KW as opposed to 4.4KW like it's expected to. When we tried unplugging 1 charger at a time, it would drop down from 3.1 to 2.2kw. So it seems like the chargepoint plug is only supplying around 15A max even though it says it's capable of 6.1kw.

I did some digging around on the J1772 protocol, and found this PWM chart:
123544


If I'm not mistaken, the PWM signal comes from the charging station's plug right? How would I be able to change the PWM to a 50% duty cycle?
 

·
Registered
Joined
·
209 Posts
That PWM stuff is for the charging station to inform the vehicle what it's capable of. It is then on the vehicle not to draw more than the capacity of the station, or the protection will trip. I don't believe any of them have any kind of current limiting capability other than just a breaker. One of your chargers must have been misbehaving again :)
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #13 ·
That PWM stuff is for the charging station to inform the vehicle what it's capable of. It is then on the vehicle not to draw more than the capacity of the station, or the protection will trip. I don't believe any of them have any kind of current limiting capability other than just a breaker. One of your chargers must have been misbehaving again :)

Ahh that makes sense, so I shouldn't even need to look at the pwm. Oh boy we'll try again and use a current meter to measure the output of both chargers then.

It's so weird because

Charger A + bike A = ~2.2KW
Charger B + bike B = ~2.2kW

Charger A + bike A + Charger B + bike B = ~3.1kW

And unplugging either one would drop it back down to 2.2kW

Well at least we know it's not the J1772 adapter, so I'll just slowly diagnose it some more and see how we can get the charger solution fixed. Thanks for your help :)
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #15 ·
Did you basically wire up something like this ? https://www.tucsonev.com/images/Zero/Zero 2 C-13.jpg
Yup pretty much, we used a 3 port plug so it could support 3 chargers.



We found the culprit. It was NOT the J1772, nor the chargepoint plug. The issue is in the weird design of the Li ion charger we got. They have a weird 8A charge speed for the first 10 minutes if the battery is under 74V. We let our bikes charge for 10 minutes, and sure enough both of the chargers ramped up to around 25A each
Rectangle Slope Line Plot Font

Road surface Asphalt Automotive tire Grey Tar

Automotive tire Gauge Calculator Crankset Measuring instrument
 
1 - 15 of 15 Posts
Top