Jump to content

Justin's DIY battery


Recommended Posts

21 minutes ago, Gnome said:

Ah ok gotcha.  Still generally you won't see anything mains related without isolation, apart from the no-isolation/shock problem, it can cause fire quite easily if you go out of range.  The operating range of your circuit is very narrow I assume (ie. very close to exactly right AC voltage required).

At least I can't think of any products I've bought that uses DC without isolation. (expect perhaps an indicator LED with a resistor in series)

The basic PSU on the main board is a pretty solid unit.  It does include a polyfuse, but it is not really necessary, as the resistances are so high that even a dead short on any of the LV components can't raise the current high enough to trip it.

 

Link to post
Share on other sites
  • Replies 60
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

Well, I finally twisted Jaco's arm into a non-blue install, and the results are beautiful... With the whole house as a dummy load, I also got a chance to properly test the battery and assorted bi

An evening's work, and the inverter is happy to think the Arduino isa Pylon battery... Now to get the two parts talking to each other...  

Thanks for all the tips guys.  Mostly incorporated and seems to work quite well. Here is a preview for anybody who wants to review it for me  : // HIGH VOLTAGE LOGIC if(bat_maxv > BAT_

Posted Images

24 minutes ago, Gnome said:

At least I can't think of any products I've bought that uses DC without isolation. (expect perhaps an indicator LED with a resistor in series)

I've seen many of those. All of them fully enclosed in some kind of flame-resistant plastic with nothing exposed so that it doesn't matter if there is no isolation. Everything from daylight switches to the V9261F-based al-cheapo plug-in energy meter. Capacitive dropper, rectifier bridge, some sort of regulation (zener, linear regulator), and then the goodies.

Link to post
Share on other sites
13 minutes ago, JustinSchoeman said:

The basic PSU on the main board is a pretty solid unit.  It does include a polyfuse, but it is not really necessary, as the resistances are so high that even a dead short on any of the LV components can't raise the current high enough to trip it.

The biggest concern isn't so much input resistance (which I assume is close to the MΩ range?).  It is the fact that the components don't fail safe.  IE> if they fail, they fail short.

Whereas transformer(s), Y class capacitors and light sources (ie. Opto) fail open (ie. safe).

Even resistors have voltage ratings.  Once exceeded, the resistor will fail short, regardless what its resistance rating was.  Ditto for diodes (I assume you used 1kV rated diodes because they are super cheap).

These failures are more common than people think.  A number of cheap-o USB chargers with no isolation were sold in China and electrocuted some people.

Again fire hazard is the biggest risk for you, assuming there is no way the thing can touch metal.  So I would just have a good way to prevent it burning the place up.

9 minutes ago, plonkster said:

I've seen many of those. All of them fully enclosed in some kind of flame-resistant plastic with nothing exposed so that it doesn't matter if there is no isolation. Everything from daylight switches to the V9261F-based al-cheapo plug-in energy meter. Capacitive dropper, rectifier bridge, some sort of regulation (zener, linear regulator), and then the goodies.

To your point, I googled V9261F and found this: https://mysku.ru/blog/aliexpress/59870.html

To get something like that legal, you probably need quite a bit of testing.  Similar to multimeter CAT ratings.  Most "reputable" voltage/current measurement equipment I've seen seem to favor current transformers rather than a shunt & direct voltage measurement like that.

But to be fair, you can get much more accurate data using a shunt & direct measurement.  It is probably just much more expensive to get through EU & US testing procedures.

Edited by Gnome
Link to post
Share on other sites
21 minutes ago, Gnome said:

To get something like that legal, you probably need quite a bit of testing.  Similar to multimeter CAT ratings.

I think the only thing you need to do is make sure nothing is exposed and that the plastic won't sustain combustion. Nobody cares beyond that point. Besides, the matter of legality assumes someone is going to police it... 🙂

Inside a DB-board, with an insurance company, there I suppose you have a good point.

Edit: Oh, and of course, you need to put a CE mark on there. No idea what it is for, but you put that on there to indicate you thought of safety... some time in the last decade.

Edited by plonkster
Link to post
Share on other sites
46 minutes ago, Gnome said:

Even resistors have voltage ratings.  Once exceeded, the resistor will fail short, regardless what its resistance rating was.  Ditto for diodes (I assume you used 1kV rated diodes because they are super cheap

Again - I have not touched the PSU board - I am using the existing PSU of an existing SANS approved geyser timer.  The PSU is poly fuse protected, and has such a low maximum current that it could never pose a fire hazard, even if you replaced my circuit board with a wire from Vcc to GND.

Link to post
Share on other sites
3 hours ago, JustinSchoeman said:

Again - I have not touched the PSU board - I am using the existing PSU of an existing SANS approved geyser timer.  The PSU is poly fuse protected, and has such a low maximum current that it could never pose a fire hazard, even if you replaced my circuit board with a wire from Vcc to GND.

Oooh I thought you designed it

Link to post
Share on other sites

Code is on github.  Still needs lots of cleanups, but some bits and pieces may be useful to others (and an extra set of eyes may help catch bugs ;) ) :

https://github.com/justinschoeman/dalybms

If anybody is going to play with this, the note in the first line is important.  Need to replace stock arduino bootloader with a recent optiboot. Otherwise the hardware watchdog causes a boot loop...

Edited by JustinSchoeman
Link to post
Share on other sites
  • 2 weeks later...

Well, I finally twisted Jaco's arm into a non-blue install, and the results are beautiful...

With the whole house as a dummy load, I also got a chance to properly test the battery and assorted bits.

Load peaked at 11kW before the geyser controller managed to turn the geyser off, and then stabilised at around 8kW, with 195A draw from the batteries.  After around 10 minutes, batteries, terminals and connecting plates were all still at room temperature.  The wires connecting to the inverter were however a few degrees warmer.  Glad I did not go smaller than the 70mm^2 I eventually settled on. (I have 2x 95mm^2 wires in parallel for joining the banks - and these wires also stayed cool.)

All in all, it has turned out to be a successful experiment so far.

Been off grid for 15 hours so far, and hope to stay that way pretty much indefinitely.

install.jpg

bat.jpg

sunsynk.jpg

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...