OpenEVSE - Open Source Charging Station

[GlennD]

I do not think I am over reacting. History has shown the EVSE works even though the voltage is completely out of spec. The original relay was the PB 30A relay with a 30A set of contacts. That relay has a 80 ohm coil and it will force the voltage well above the logic max. CMOS is not TTL and it works fine out of spec but it is not right. I do not have any data of the total coil resistance of the PB single pole relays Chris favors in pairs.

I will either use Barbouri's board with a proper regulator or add one to the plus boards. Just because it works out of its specifications does not make the design right.

 

[chris1howell]

I do not think I am over reacting. History has shown the EVSE works even though the voltage is completely out of spec. The original relay was the PB 30A relay with a 30A set of contacts. That relay has a 80 ohm coil and it will force the voltage well above the logic max. CMOS is not TTL and it works fine out of spec but it is not right. I do not have any data of the total coil resistance of the PB single pole relays Chris favors in pairs.

I will either use Barbouri's board with a proper regulator or add one to the plus boards. Just because it works out of its specifications does not make the design right.

The relays reccomended and included in the kits have 144 ohm coils. When using two relays there is a slight staggering of each relay.

OpenEVSE is a community driven project. I would much rather be constructive than just shout "the sky is falling". I am more than happy to make improvements to the design. In fact now is a great time as I am revising the DIY boards to add current measurement.

Glenn I know you have several complaints and modify the boards you build. Please send me details of your modifications and I can incorporate your improvements. I have read posts that you feel I do not use enough capacitors in the design and you add your own. I have also read you use a different opamp for your pilot. I can add a zener to keep 5v within spec.

 

[QueenBee]

This may account for some of the times my OpenEVSE has hung.

I have no idea if that would contribute but I've had mine lock up at least 2 or 3 times as well.

 

[GlennD]

I am sure the processor will work on a range of voltages. It works at 3.3V with a 8MHZ crystal. The display is rated for 5V plus or minus .25V. You can see it brighten when the relays pull in for the line sense.

To me the big problem aside from exceeding specs is the spike on the 5V line. Spikes are evil and they can cause many problems.

 

[garygid]

Generally, I agree with Glenn, that with a non-regulated logic power supply,
and any spikes on the power supplies, it is very likely to cause trouble, even
if not often detected in normal use.

For something like the EVSE, used with expensive vehicles, it is by far
best to change the design to use a properly regulated and filtered
5v supply for the logic, even if that means finding a new power module.
Just putting a zener on the outout is only a bandage on an open wound.

I would not have known that the dual voltage supply had a non-regulated
5 volt outout. Thanks Glenn.

Chris, thanks for all your excellent work. I encourage you to continue
your dedication to improving quality and doing things splendidly.
Cheers, Gary

 

[GlennD]

Generally, I agree with Glenn, that with a non-regulated logic power supply,
and any spikes on the power supplies, it is very likely to cause trouble, even
if not often detected in normal use.

For something like the EVSE, used with expensive vehicles, it is by far
best to change the design to use a properly regulated and filtered
5v supply for the logic, even if that means finding a new power module.
Just putting a zener on the outout is only a bandage on an open wound.

I would not have known that the dual voltage supply had a non-regulated
5 volt outout. Thanks Glenn.

Chris, thanks for all your excellent work. I encourage you to continue
your dedication to improving quality and doing things splendidly.
Cheers, Gary

I also had no Idea the 5V was a tack on. I have always assumed any voltage on a power brick was fully regulated. I only started checking it when the spike corrupted the eeprom on the unit I was building.

There is plenty of room to go back to a surface mount regulator around the module. No new module is needed. In fact since the DC to DC converter now runs on 12V it should run stone cold.

 

[chris1howell]

Generally, I agree with Glenn, that with a non-regulated logic power supply,
and any spikes on the power supplies, it is very likely to cause trouble, even
if not often detected in normal use

Output 1 is regulated to 1% max.
Output 2 is regulated to 5% max.

I would not call 5% non-regulated or junk.

 

[GlennD]

With the minimum loads it is regulated to 5%. The way we operate it there is only the very light load of the opamp and associated parts on the 12V, then wham, using your 2 relays at 77 ohms a 155Ma load.

Enough, you go your way and I will go mine. I like your size factor but I will add a regulator.

 

[Barbouri]

I will either use Barbouri's board with a proper regulator or add one to the plus boards. Just because it works out of its specifications does not make the design right.

After reading the concerns about the 5V regulation, I decided to connect the digital scope to a DIY V4.21 board with a 70 ohm relay. The 5V output at the processor reads 4.98 VDC.
Switching the relay on or off caused no detectable variation in the 5V regulation that exceeded the normal power supply ripple voltage.
I have had several people complain about the cost of the switching regulator chip and all the decoupling capacitors on the V4.xx series boards, but I feel this is an example of you get what you pay for.

The OpenEVSE plus board that Chris designed is a robust and compact system.
The part of the design that I have always felt was a potential problem area, was the lack of decoupling capacitors located on each IC's power pin.
Here is a quote from Atmel the makers of the microprocessor chip.
"One of the most common reasons for EMC problems with microcontroller products is that the power supply is not good enough. Correct and sufficient decoupling of power lines is crucial for stable microcontroller behavior, and for minimizing the emitted noise from the device."
http://www.atmel.com/Images/doc1619.pdf
http://www.atmel.com/images/atmel-2...gn-considerations_application-note_avr042.pdf

Greg C. (Barbouri)

 

[GlennD]

I have on hand a surface mount Plus board belonging to Tony Williams. It is about a year old. It tests much better than the current production units.

With a RGB display connected it measures 4.84v. With a 68 ohm resistor simulating the relay it read 5.16V.

With the minimum loads described on the spec sheet it read 4.3V. increasing the 12V load to a 68 ohm resistor changed the 5V to 4.69V

Clearly something internally has changed.

 

[mitch672]

I think we need to calm down and talk things out, I'd rather not see OpenEVSE splintered into different waring factions. Maybe we need some arbitration to come to agreement here.
http://dictionary.reference.com/browse/arbitration" onclick="window.open(this.href);return false;

 

[kubel]

OpenEVSE is an open source project. One can either suggest their improvements for future revisions and work within the project, or the source can fork off in another direction by someone with the ambition to do so if they feel it's necessary. It sounds like Chris is very open to suggestions at this point for future boards, while others are taking a 'sky is falling' approach.

 

[pchilds]

From Glenn's last post, the problem may be limited to a bad batch of power bricks. I have a year old OpenEVSE Plus, that I am pushing the power brick to its limits and a OpenEVSE with the built in relays. I will test them both and report back.

 

[GlennD]

I do not think it is a batch of bad modules. I think they changed it for a customer that needed more 5V and relativity static loads. Otherwise the recommended min would not load the 5V below spec on the older units.

 

[pchilds]

Sorry, I mis-read/remembered your post.

 

[GlennD]

I just received and tested 2 power modules bare, not installed. Neither one meets digital specs. The older module on Tony Williams Plus board about a year old was much better.

Module 1

Unloaded
11.974V 5.589V
Minimum load is 12V 180 ohm and 5V 120 ohm resistors

11.972V 5.036V The 12V seems constant so I stopped measuring it

5.461V 68 ohm simulating a relay plus the min resistors

Module 2

Unloaded
12.013V 5.613V

Minimum load
12.180V 5.031V

All measurements are with the min load resistors in place
5.140V 200 ohm
5.237V 100 ohm
5.334V 68 ohm relay simulate
5.427V 50 ohm

They are much better with the min load but as we use them the 12V is barely loaded and the 5V basically has the light load of the display( if fitted ). The board CMOS chips draw next to nothing and the processor is from the pico power line.

All measurements were from a HP 4368 6 digit DVM calibrated to at least 5 digits. That is all the calibrator I borrowed could do.

 

[Bob]

I just looked at the Atmel data sheet. You probably already know this, but they specify operation up to 6V, and guarantee performance specifications with supply from 1.8V to 5.5V. Based on that, the data Glenn has showed, my 35+ years in the semiconductor industry, and my hand analysis of the design, I'm feeling pretty good about the OpenEVSE as is.

Could it be better? Yes. Anything can be improved.

Is anything wrong? Not in my opinion.

Bob

 

[chris1howell]

Thanks for the data Glenn. I have been testing boards and supplies I have here and am having trouble reproducing your results. I am not sure what is going on but I know we will get to the bottom of it and fix the issue.

The last board I tested was built recently and is an OpenEVSE PLUS built in the most common configuration (90% of orders). 2 30a relays and display. I measured at the FTDI header pins. Here are my readings.

Idle 4.87
Charging 5.02

I am not 100% certain the Power supply came from the same batch as Glenn's so I am building another now with a supply from the same box.

One question for Glenn...Are you using the recommended low ESR capacitors on the power outputs?

 

[GlennD]

The readings I posted were from the raw modules as is with no additional components except for the load resistors. I did not use a relay but a 68 ohm resistor in place of it for testing. I think with the addition of two load resistors it is acceptable but the display is slightly out of spec but it works.

I will test module 2 in circuit when I build the second board up. I used an external regulator on the first one.

 

[GlennD]

OK, I tested module 2 date code 1419 in a DIY Plus unit

5.013V unloaded

5.472V 68 ohm resistor

5.019V unloaded with RGB display

5V spike present

With a 180 ohm 12V load and a 120 ohm 5V load and display.

4.854V with no relay load

5.378 with a 68 ohm resistor.

With the 180 ohm resistor on the 12V the 5 V spike is totally gone upon removing the 68 ohm load. The 5V load stabilizes the voltage.

If seems to me that if you add the factory recommended min loads the EVSE is quite satisfactory. My biggest concern, the 5V spike is totally gone.


Oops, I should not rely on my faulty memory. The 5V load should be 160 ohms ( actual 167).

Well Fry's it starting to look like Radio Shack as far as the parts selection is concerned. In 2W they only had 220 ohms and in 1/2W they only had 180 ohms. Both units work fine with these values. I was originally using a 180 ohm 1W for the 12V load but even though the load was .8W it ran hot.