oldswamm wrote:ga2500ev, my board would be isolated from the mains with a transformer, but it's 'ground' would connect directly to the Batt-. Any other setup would make current measurement problematic. In that case, I don't see why a voltage divider wouldn't be fine for B+ measurement.
oldswamm wrote:I'm confused. What are you going to do with the pic on the mains side? Are you going to measure something there?
The solid state relays are already isolated, and that's all I figured on having on the mains side.
My board would be at Batt-, and there's no practical way to isolate it that I can see.
I would ground the case, and the only thing not enclosed would be the battery.
The battery leads are connected to the mains, but heck, the battery is dangerous at 24s or more even without this.
<edit> Do you have a plan to isolate the battery from the mains? Because the battery is dangerous,it should be totally isolated, and well insulated whether using this charger or not. <endedit>
Throw up a sketch, so we can see what the extra processor is for. It would be nice if we could come up with a cooperative design. The way things usually work on ES is there's discussion, then everybody does their own design. If you have a better way than I can come up with, and it's not to expensive, I'm fine with going with your design.
P. S. for those of you who want one of these chargers, but don't want to build one, you can buy it here.
I don't think I would want to be their insurance provider, though.
oldswamm wrote:You STILL haven't said WHY the processor board has to be isolated from the battery (and consequently the AC power).
If you have the case open with power to it, the rectifier, the caps, the secondary processor (if used), and the battery connections have dangerous voltage available any way, so who cares if the primary processor board does also. If you have ANY AC powered appliance open, with power to it, don't touch ANYTHING!
What country do you live in that doesn't have polarized power connectors anyway? (Would be nice if you filled in that info in your profile.)
Here in the US we have 3 (or 4) pole outlets for 120 or 240V, all of which include a ground connection (and 2 prong plugs are 'polarized' as well). (I thought all countries had grounded outlets these days.) I fully intend to use a metal case and 3 conductor GFCI.
So, the cardinal law of working around live circuits is to assume that the neutral conductor is at the same potential as the hot wire.
Said ground connection would be connected to the case, so any short to the case will trip the GFCI. The polarity of the connection to the caps shouldn't really matter. The battery will have AC to it no matter what, and that's the only place the operator could come in contact with it, (if it isn't insulated). That's why I stated that the battery should be well insulated (not to mention that it's dangerous even without the charger connected if it's high cell count).
SCRs won't work, unless you use 2 back to back. You need AC to the caps. You need to use triacs with optoisolators, commonly called 'AC solid state relays'.
If you ARE going to use 2 isolated processors, you would be far better off using serial communication. That way you won't lose ANY accuracy, and can eliminate all the RC and the op amp, and can send the current info over the same connection (unless you were going to use a 3rd processor for current measurement). I'm afraid I probably wouldn't use your design if you add the extra complication, though, unless you can come up with a valid reason.
Thanks for the link for caps.
<edit>They don't give full specs (they say they're smaller than other peoples, but don't give the dimensions ), not even the brand name, and when I tried to email them, the email address they give is bogus. I think I'll stick with brand name even if it costs more.
I take it you live where there's more current available from the standard outlet than in the US, or are you going to use less common high current connections to get your 30A? If you use 220V line you will get more than 30A from 800uF, won't you? <endedit>
Did you notice that that 'commercial' charger doesn't use a grounded outlet, or apparently GFCI?
<also edited for grammar.>
ga2500ev wrote:oldswamm wrote:You STILL haven't said WHY the processor board has to be isolated from the battery (and consequently the AC power).
Because it's not isolated from mains power.
oldswamm wrote:I already conceded!
I have a full set of schematics drawn, but got busy.
I'll try and post them tomorrow if I get time.
oldswamm wrote:Is there a way to distinguish between the term for a high cell voltage monitor digital output, and the voltage across the entire battery.
In this thread HVC seams to stand for the voltage across the entire battery, whereby I thought it stood for 'high voltage-cell'. Apparently this is another acronym that has multiple meanings, which is confusing.
Do we need to come up with a new acronym for the voltages across the high and low cells, which are our real limits with lithium batteries?
Maybe we should start using HCV even though that makes it sound like an analog value rather than digital, and of course then all the BMS and HVC/LVC monitor manufactures would have to change their terms, which they aren't going to do since their outputs mean one cell is high or low.....
I guess I'm going to have to use the more verbose term 'High Voltage-Cell'. Hard to fit on a schematic though....
oldswamm wrote:Any old timers want to weigh in as to what HVC stands for? I did a google search and the closest I found, out of over 50 definitions, was 'high voltage circuit' and 'high voltage capacitor'.
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