# designing a 'set and forget' charger ?



## Tahoe Tim (Feb 20, 2010)

+1

a true "consumer friendly" charger


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## DIYguy (Sep 18, 2008)

No one wants to jump in ...yet... I think it's a great idea Dan. For those who don't want to run with a BMS... ya, others may throw a few stones. .. but there are definitely some advantages of what you suggest. It can definitely be built. I haven't seen anything like it. It's kind of like a "top-only" monitoring or *CMS*. (charge monitoring system) 
I would suggest though...that perhaps the best way is to build a pony-box or separate box... and just send output to charger to switch modes. (like some do now with contactors). This way, you could use it with any charger. 

Of course the charger features you speak of would have to be there...but I think these exist now...

Just my $.02

Sorry Tim...lol, u pulled the trigger b4 me...lol


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## tomofreno (Mar 3, 2009)

> so my question is whether there is already a simple foolproof relatively inexpensive charger like this I don't know about


 Yes, A minibms (around $500 for your 38 cells) and a Zivan or Chinoz charger. And you don't need 50 connections. Just one wire between cell level boards and to the main board, and connection of the main board to 12VDC and to an AC relay to shut off power to the charger at an HVC event. Schematics are on Dimitri's website. Downside is you get no choice on the cell limit voltage - which would be nice I agree. Seems to me what you are describing is essentially a charger with built in bms.


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## Franky.EV (Feb 27, 2010)

rwaudio, A guy in this forum who is converting a porsche, build a charger whith lot of DC/DC, charger design


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## rwaudio (May 22, 2008)

dtbaker said:


> ...been thinking a lot about what I WISH was available as far as a charger goes, and not being an EE, I want to just put the functional requirements out, and ask if anyone can put it together, or maybe already has?
> 
> first some assumptions/goals:
> - as a mechanical DIY guy, I am not interested in huge amounts of flexibility, data recording, etc. I want to 'set it, and forget it'.
> ...


My goals are the same as yours but my implimentation is a bit different, but I did cover the monitoring, indivdual current ramp, adjustable finish voltage etc. The only thing left to prove is reliability. If it works as well as it should I will make it available to others.
http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/
There is also the capability of SOC, high cell, low cell, avg cell, total pack voltage, current etc.


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## dtbaker (Jan 5, 2008)

tomofreno said:


> Yes, A minibms (around $500 for your 38 cells) and a Zivan or Chinoz charger. And you don't need 50 connections. Just one wire between cell level boards and to the main board, and connection of the main board to 12VDC and to an AC relay to shut off power to the charger at an HVC event. Schematics are on Dimitri's website. Downside is you get no choice on the cell limit voltage - which would be nice I agree. Seems to me what you are describing is essentially a charger with built in bms.


exactly... either a new simple charger ground up w/ integrated HVC cutoff, or a nice clean add-on black box with a simplistic cell limit stuff all inside that would be installed basically as an interlock or pass-thru on the AC power to the charger and kill it when the first cell hit limit. A settable cell limit would be nice, but not required if it makes it much more expensive... just some reasonable setpoint like 3.70 would be fine. Visual indication of which cell was first, and which ones were close would also be nice, but not required.

The hope I would have is that if you have a reliable cutoff based on the cell limit, the charger might be a lot simpler, really with no settings for different pack voltage or curves... assuming you are ok with a simple CA charge up to some limit, and off. 

an extra $500 for a mini-BMS add-on is getting approachable, but still too expensive for my taste. My question is if it were simpler and more hard-coded, could it be sold for significantly less?


I suggested a set of 50 terminal blocks just to cover the likely config of up to one wire per 48 cells, plus one.


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## Tesseract (Sep 27, 2008)

dtbaker said:


> an extra $500 for a mini-BMS add-on is getting approachable, but still too expensive for my taste. My question is if it were simpler and more hard-coded, could it be sold for significantly less?


It is highly unlikely the miniBMS could be made any less expensive. Unless it were mass-produced with all SMT components, no "flying" ring terminal and/or "some assembly required" by the end user. 

Your idea is to basically put a BMS inside the charger which, of course, makes the charger more expensive. How much more expensive? Oh, about the same as having a separate BMS module on each cell. 

So, same difference.

Integrating the BMS and the charger makes sense - to me, anyway - if it is for single-cells or, at most, 4 cells in series.

Making a series pack charger "set and forget" is certainly doable. Making it so it draws a maximum of 15A from 120V and, say, 30A from 240V is also doable. Making it so it doesn't change setpoint when going from 120 to 240V is also doable (as well as not blowing up if accidentally disconnected from the battery pack... )

So, many of your goals/desires make perfect sense to me, just not integrating the BMS and charger in one box (as long as there is an input that shuts off the charger if a cell hits HVC).


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## todayican (Jul 31, 2008)

Hmmm "Chargiton 1"?


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## Elithion (Oct 6, 2009)

dtbaker said:


> .. what I WISH ... charger... monitoring individual cells.


Chargers with built in Li-Ion BMS to protect from cell over-voltage do exist. The BMS runs only when the charger's BMS runs. 

To protect against cell under-voltage you need a second BMS, one that runs when discharging. So, instead, you might as well have just a single BMS to protects cells from both under-voltage and over-voltage, and that runs both when charging and discharging.

Davide


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## rwaudio (May 22, 2008)

todayican said:


> Hmmm "Chargiton 1"?


Lol I was thinking the same thing. But lets start off with the Chargiton 0.01, no way to power a 300kw charger yet


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## LiFe (May 24, 2010)

I agree with Tesseract -you'll just have leave out the CV/CC control based on cell level monitoring.


IMHO what a conversion builder wants is a comprehensive package that includes amp hour counting, cell level monitoring, easily configurable, easily installed, and can be integrated into an existing vehicle instrument panel (SOC gauge, temp, etc), along with an integrated 120v/240v charger that can accept most any source and not pop a breaker. And exhibits some tolerance to installer mistakes. Example; an optical coupled BMS that configures itself as a daisy chain repeater, easily identifying the problem link, besides complete rejection of EMF.

Bonus points awarded for a standardized I/O package to communicate with motor controllers. Such as current limiting based on SOC/pack temp, charge interlocking, etc.

What you see in the market now are engineering projects being passed off as engineered products.

They're produced by an individual, with mediocre hardware design discipline, or a bit twiddler who integrates what they believes are important features. Sometimes the features have nothing to do with market reality, and distract from a solid and validated system design.

Then when you include less-than-adequate social skills it often results in a somewhat alienated customer base. 

I've watched these characters throw darts for awhile now. 


Ready to belly up there Mr. Tesseract?


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## dtbaker (Jan 5, 2008)

Elithion said:


> (Just don't call it a "BMS", because that term seems to have negative connotations in some circles.)


Its not the term 'BMS' that bothers me, its the cost.... 

I pretty think that the ignoring undervoltage issue is plain driver error. I think any active shut-down of the system versus a simple idiot light has pros and cons with unexpected limp mode, etc, and I would rather rely on SOME awareness of the SOC with a decent SOC meter that counts ah for the typical Li setup.

I am thinking a standalone box that just watches for HV on any input leads you plug into it, and is maybe a pass-thru for the AC power with a relay to the charger might be the simplest and cheapest. Many of the cheaper chargers don't have any way to shut them down externally, so perhaps just a relay on the AC input would 'fit' the most chargers and be an easy aftermarket.

How about this? Given these very modest design goals, what do you think?


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## DavidDymaxion (Dec 1, 2008)

rwaudio said:


> My goals are the same as yours but my implimentation is a bit different, but I did cover the monitoring, indivdual current ramp, adjustable finish voltage etc. The only thing left to prove is reliability. If it works as well as it should I will make it available to others.
> http://electricporsche.rwaudio.com/2010/11/electric-porsche-charger-design/
> There is also the capability of SOC, high cell, low cell, avg cell, total pack voltage, current etc.


Great stuff, thanks for posting that on a web page.



rwaudio said:


> Lol I was thinking the same thing. But lets start off with the Chargiton 0.01, no way to power a 300kw charger yet


Except to tow a car with regen behind a truck or use a dump pack. That's still a lofty goal!


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## tomofreno (Mar 3, 2009)

> IMHO what a conversion builder wants is a comprehensive package that includes amp hour counting...


 You left out one important point...they want all that for less than $1000.00


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## dtbaker (Jan 5, 2008)

tomofreno said:


> You left out one important point...they want all that for less than $1000.00


yes, like $500 would be good.  Just as a market reference point and considering the cost of controllers, motors, and batteries..... $500 feels about right for a charger that would truly do the job in a worry-free way. 

Just the basics of charging, and protecting against overcharge of any single cell would be great for the DIY person using large format cells, or at the string level for the smaller headway-ish cells.

Instrumentation, over-discharge warnings, ah in/out can all be handled by meters and displays.


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## Tesseract (Sep 27, 2008)

LiFe said:


> What you see in the market now are engineering projects being passed off as engineered products.


That's a somewhat incendiary way of putting it, but I tend to agree with your characterization. There are two reasons for this state of affairs, however, which I feel it is only fair to point out: 1) very few people in the entire world convert their vehicles to electric every year so there isn't much volume for EV products; 2) most of those people are terminal cheapskates that balk at even paying even $10 per cell for a BMS.

Point 1 prevents there ever being the economies of scale to satisfy Point 2, hence why most (all?) BMS offerings are either science projects or priced like they were for the military.



LiFe said:


> Then when you include less-than-adequate social skills it often results in a somewhat alienated customer base.


I probably fit this description. That's just typical of engineers, I've noticed, but I, at least, don't feel particularly apologetic about it. Which is also typical of engineers...




LiFe said:


> Ready to belly up there Mr. Tesseract?


Yeah, a smart charger is in the pipeline but we aren't real interested in making a BMS, mainly because there is so little profit to offset so much liability, but also because I truly feel that Jack Rickard's active campaigning against using a BMS is depressing any further innovation here. I know I certainly don't feel like butting heads with him over this again.




dtbaker said:


> ...$500 feels about right for a charger that would truly do the job in a worry-free way...


Maybe if the annual sales volume were in the tens of thousands, which is definitely not the case now - something along the lines of 100's per year is more realistic. There simply aren't enough economies of scale to push pricing down from "boutique" to "commodity", and you are definitely thinking "commodity".

Even $1000 might be too low unless the power rating is very modest.

Also keep in mind that anything that connects to the AC mains is supposed to be UL and FCC/CE listed. Testing for compliance with these safety and EMC regulations can cost more than developing the product in the first place.


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## dtbaker (Jan 5, 2008)

Tesseract said:


> Also keep in mind that anything that connects to the AC mains is supposed to be UL and FCC/CE listed. Testing for compliance with these safety and EMC regulations can cost more than developing the product in the first place.


if we scale the project to a black box that has an AC plug to the wall, and an AC plug thru to the charger... and the relay inside that is connected to the AC is UL listed.... does the black box have to be UL as a whole new thing?

All the little stuff monitoring voltage, and deciding to cut the power is not 'really' connected to the AC, so I am wondering if it really needs UL?

I guess what I am looking for is the cheapest possible safety net so that if any one cell suddenly becomes unbalanced and goes ballistic, the charger shuts down. Worst case failure for the charge monitor is that you are no worse off than with just the charger... with no chance of the monitor affecting batteries other than turning off the charger.


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## tomofreno (Mar 3, 2009)

> yes, like $500 would be good.


 Dan, look at the price of the cheapest Charger you can get from China which has none of the features you are asking for, then estimate the cost of those added components. 



> That's just typical of engineers, I've noticed, but I, at least, don't feel particularly apologetic about it. Which is also typical of engineers...


 Speak for yourself Jeff.


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## todayican (Jul 31, 2008)

Engineer = Someone who dreams up ways of doing things, then does them.
Ungineer = Someone who gets in the way of an Engineer with speculation and detractory


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## dtbaker (Jan 5, 2008)

tomofreno said:


> Dan, look at the price of the cheapest Charger you can get from China which has none of the features you are asking for, then estimate the cost of those added components.


well.... the retail price on a simple Elcon 1500 is down to $525, so we're not that far off. I would hope that the actual component cost of a simple monitoring system would only cost a few dollars in parts, but would guess a relay capable of cutting the AC power might cost a little more, but not hundreds more.

I am just a 'get it done' mechanical guy looking for a simple safety net, and yes as economically as possible. I am HOPING that cell balance doesn't drift very much or at all and the safety net is never used, so hate the thought of paying very much for it. Kinda like insurance; I hate paying for that too.

and no, I am not apologetic about being a cheapskate.  I do appreciate good engineering, and am perfectly willing to pay for it when it is mission critical, and will even pay a little more when made in the USA to support our economy.


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## Tesseract (Sep 27, 2008)

tomofreno said:


> Speak for yourself Jeff.


Gee, I thought it was pretty obvious that I WAS speaking for myself, Tom. Or it was, anyway, until you lopped off the part where I said, "I probably fit this description." Also, I did say that the _typical_ engineer was guilty of said faults.... last time I checked, using the word typical implies that there are members which are atypical. You are certainly free to be part of the atypical group, Tom, but making this kind of comment without any provocation whatsoever sort of puts you squarely in the typical camp. Ironic, eh?




dtbaker said:


> well.... the retail price on a simple Elcon 1500 is down to $525, so we're not that far off. I would hope that the actual component cost of a simple monitoring system would only cost a few dollars in parts, but would guess a relay capable of cutting the AC power might cost a little more, but not hundreds more.


1.5kW isn't much of a charger, though, especially when you have a 15kWh or larger battery pack. This is the kind of "penny wise/pound foolish" mistake that renders a perfectly good EV impractical, in my opinion. I mean, a 1.5kW charger is only going to give you 5 miles of range for every hour you wait with most vehicles, and few have that kind of patience or route-planning skill.

Of course, that _is_ close to the max you can pull from a 120V outlet, so not really a limiting factor in this case, but IIRC, Elcon chargers deliver a set maximum power output regardless of the supply voltage so connecting them to a 240V outlet won't get you anything besides half the amp draw right when you don't need it.

In my opinion, spending twice as much and getting twice the power and maybe smarter functions seems like a very worthwhile trade-off.

Finally, the parts cost to monitor cell voltage might not be more than a few dollars each, but you are multiplying that by 50-100x and then there is the labor required to populate them and even more so the labor to QC test each channel, etc. With products like this the parts cost might be less than half the minimum wholesale price, and one-third or less of the retail price.


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## tomofreno (Mar 3, 2009)

> I probably fit this description. That's just typical of engineers, I've noticed, but I, at least, don't feel particularly apologetic about it. Which is also typical of engineers...





> Gee, I thought it was pretty obvious that I WAS speaking for myself, Tom. Or it was, anyway, until you lopped off the part where I said, "I probably fit this description."


 Ok, your original full quote is above. My response was with regard to the phrases "that's just typical of engineers, and "which is also typical of engineers". If your sample is representative of all engineers, then I am an atypical case. My experience during about 20 years as a development engineer, engineering manager, and project manager, and working with engineers at companies such as Hitachi, Fujitsu, Samsung, TSMC, Intel, TI, and IBM is that I am more toward the typical case. It may well vary with company size.


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## DIYguy (Sep 18, 2008)

Hey Dan,

Was thinking about this a bit. I tend to agree that you could put this together with less than what has been deemed necessary and without a full blown pack BMS built into the charger. . . mainly because you aren't looking for all the features of a typical BMS. I suggested the separate box for this reason and to make it able to fit different charger applications. 
Another thought however....based on some of the practical side perspective.
(. I'm an engineer also...atypical based on criteria submitted....lol) Since you are wanting to go without an on board BMS...and therefore will be doing some active monitoring etc... I would suggest maybe you could identify the 3 or 4 or 5 cells that tend to hit top knee first (based on some of JRP's experiences...he watches a few of them)... and since there are only a few to use as control over the pack charge.... MiniBMS on these 3 - 5 cells, with a head end board and power relay for the charger, you could get the best of both worlds. This isn't for everyone, but for "active users" who know their pack and check it .... could be a decent solution. 

I would think that the few identified "control group" of cells that exhibit top charge out first, would tend to remain as such... that may be a question... but I'm thinking they should. Either way occasional checking would take care of this.

anyways...just thought I would throw that out there..


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## DIYguy (Sep 18, 2008)

Tesseract said:


> Elcon chargers deliver a set maximum power output regardless of the supply voltage so connecting them to a 240V outlet won't get you anything besides half the amp draw right when you don't need it.


Hi Jeff, this statement caught me by surprise. I have a 6kw Elcon and I am relatively sure (now u got me thinking) that it charges closer to 15 amps when plugged into 120VAC and about 27 amps when connected to 240VAC.

Edit... ok, so I had a look at the manual. The example they showed was for a 48 volt output charger. Sure enough, the current was 25 amps on 220 and 24.5 amps on 115VAC. I'm wondering about chargers for higher pack voltages. Can you still output say 27 amps to a 192 volt pack (uses voltages up to 250VDC) when connected to 115 VAC?


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## dtbaker (Jan 5, 2008)

DIYguy said:


> ...so I had a look at the manual. The example they showed was for a 48 volt output charger. Sure enough, the current was 25 amps on 220 and 24.5 amps on 115VAC.


so... although the 1500 at 110v is probably best used with average range of 50 miles or less (using less than 10kWhr) because of charge time, wouldn't getting 15 amps at 220v in yield twice as much kWhr as 15amps at 110v in the same amount of time?


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## dtbaker (Jan 5, 2008)

DIYguy said:


> I would suggest maybe you could identify the 3 or 4 or 5 cells that tend to hit top knee first .. MiniBMS on these 3 - 5 cells, with a head end board and power relay for the charger,


If I am going to manually watch the cells, then I don't see what a mini BMS gets me; I doubt they drift very fast, and HOPE they don't drift much at all and the point is moot. we''l see.

I only started the thread to see if there is an super economic way to build a limited function box designed only to prevent overcharge on any single cell. Hoping that with limited functional spec, the projected cost could be brought way down.

I am personally ok with checking cells manually, but looking for an inexpensive non-DIY solution in case I ever build or sell a car to a non-DIY person.


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## DIYguy (Sep 18, 2008)

dtbaker said:


> If I am going to manually watch the cells, then I don't see what a mini BMS gets me; I doubt they drift very fast, and HOPE they don't drift much at all and the point is moot. we''l see.


The suggestion was to watch the cells mainly to determine the ones hitting top charge first. . . then use these cells to inititiate charge control for the pack. I tend to agree that a BMS is not required but, if you only need to watch 3 - 5 cells.... $12 each for MiniBMS is likely the cheapest way.


dtbaker said:


> I only started the thread to see if there is an super economic way to build a limited function box designed only to prevent overcharge on any single cell. Hoping that with limited functional spec, the projected cost could be brought way down.


 Yes, I understand. I have similar ideas... so, I'm trying to help. I think this brings it down to around $100....


dtbaker said:


> I am personally ok with checking cells manually, but looking for an inexpensive non-DIY solution in case I ever build or sell a car to a non-DIY person.


Once u ID the few cells leading the race to the top... u wouldn't have to check the whole pack too often...


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## DIYguy (Sep 18, 2008)

dtbaker said:


> wouldn't getting 15 amps at 220v in yield twice as much kWhr as 15amps at 110v in the same amount of time?


Dan, yes, potentially, but Jeff was talking about output power. . . and reading his post again, he mentions "set maximum power"...meaning output to the batteries. 
I suspect the output could be less...meaning not always the same. I know when I wired my Elcon 6kw to 240VAC after using it on 120VAC, it charged much faster.


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## dimitri (May 16, 2008)

DIYguy said:


> The suggestion was to watch the cells mainly to determine the ones hitting top charge first. . . then use these cells to inititiate charge control for the pack. I tend to agree that a BMS is not required but, if you only need to watch 3 - 5 cells.... $12 each for MiniBMS is likely the cheapest way.
> Yes, I understand. I have similar ideas... so, I'm trying to help. I think this brings it down to around $100....
> 
> Once u ID the few cells leading the race to the top... u wouldn't have to check the whole pack too often...


Having BMS modules on some cells and not others is a bad idea. Parasitic loads of even a few milliamps on cells with BMS modules will cause a long term imbalance and will create more problems than it would solve. All cells in the pack must have same parasitic loads or none at all.

Even 1 mA load on a cell will eat 1AH in just 40 days.

I have done everything I can to keep MiniBMS affordable, if you can't spend $12 per cell for BMS, then you might as well go without BMS at all. The jury is still out which way is more cost effective in the long run, there are too many variables. Some people put value on different things than others, makes it impossible to make a general statement on the subject of overall battery management cost. Unless, of course, making empty general statements is your career, then you can have a field day in this area ( obviously this last remark was not toward anyone in this thread )


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## DIYguy (Sep 18, 2008)

dimitri said:


> Having BMS modules on some cells and not others is a bad idea. Parasitic loads of even a few milliamps on cells with BMS modules will cause a long term imbalance and will create more problems than it would solve. All cells in the pack must have same parasitic loads or none at all.
> 
> Even 1 mA load on a cell will eat 1AH in just 40 days.


Yes, that's a good point..I hadn't thought of. I guess the purpose or main thrust of my suggestion is to monitor only the cells that would reach upper knee first. Perhaps a separate device is needed then with a separate power supply. (Then again...a small parasitic load on these particular cells...might actually balance them better... 
What is the power requirement for the Centralized board? Perhaps this would work with a separate power source. 



dimitri said:


> I have done everything I can to keep MiniBMS affordable, if you can't spend $12 per cell for BMS, then you might as well go without BMS at all. The jury is still out which way is more cost effective in the long run, there are too many variables. Some people put value on different things than others, makes it impossible to make a general statement on the subject of overall battery management cost. Unless, of course, making empty general statements is your career, then you can have a field day in this area ( obviously this last remark was not toward anyone in this thread )


??? ya, ... ok.


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## tomofreno (Mar 3, 2009)

> wouldn't getting 15 amps at 220v in yield twice as much kWhr as 15amps at 110v in the same amount of time?


 You are talking the AC side - 220VAC/15A. If you are charging your 38 cell pack, pack voltage during charge would be around 128V I would guess. Then you would put a bit less (due to charger efficiency) than 15*220/128 = 26ADC into the pack when drawing 15A AC from the wall at 220VAC with a PFC charger. If I recall correctly, I draw about 16A from my 240VAC outlet (usually between 238 and 242V) when charging at 30ADC with pack at about 121V during charge, so about 94% charger efficiency - been a while since I checked, but that is the number I recall.

I think if you charge the same pack with 110VAC/15A you will put a bit less than 13A into the pack.


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## Tesseract (Sep 27, 2008)

DIYguy said:


> Dan, yes, potentially, but Jeff was talking about output power. . . and reading his post again, he mentions "set maximum power"...meaning output to the batteries.
> I suspect the output could be less...meaning not always the same. I know when I wired my Elcon 6kw to 240VAC after using it on 120VAC, it charged much faster.


Ah, you are trying to extrapolate how your 6kW charger ought to behave from that of the 1.5kW charger that dtbaker mentioned. I suspect what you are ignoring is that there are different things limiting the maximum output in each case.

First off, 2kW is about all you can get from a 120V outlet, and even then you are likely going to trip a 20A breaker after a few minutes unless there is nothing else on that circuit. So a 1.5kW charger can deliver its full output whether connected to 120V or 240V; i.e. - the current draw at 120V input will be double that at 240V.

As you go higher in power, though, the ratio between current drawn at 120V and at 240V starts to come closer to 1:1 because the PFC front end (which typically provides a constant 400VDC) will have to limit the current draw from a 120V line to - ideally - less than 20A.

So, there is an unfortunate double penalty here: you have much more current available on 240V branch circuits (50A on the range circuit is common) but you need much more current at 120V where it isn't available because the maximum allowed breaker size is 30A (and even that is very uncommon compared to 20A).

If the PFC front end can handle 25A of current then it will only be able to fully meet the demand of a 6kW charger stage when it is powered by 240V (240 x 25 = 6000); when powered by 120V it can only deliver 3000W to the charger stage before it's current rating is exceeded (regardless of what the 120V circuit can actually supply). Conversely, the PFC front end in the 1.5kW charger could deliver twice as much power when powered by 240V as it does at 120V, but now the current rating of the charger stage is the limiting factor.

So there are various limits that are interacting here, but whichever one is the lowest is what is actually setting your output power. I know that's sort of stating the obvious, but, well... sometimes the obvious is the easiest to overlook.


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## DIYguy (Sep 18, 2008)

Thanks for that explanation Jeff, very good. I knew my charger was outputting more on 240VAC... So, I guess the point about the Elcon having a set output regardless of input voltage is only accurate for the smaller chargers then... . and up to the output power rating of the unit.


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## Tesseract (Sep 27, 2008)

DIYguy said:


> ...So, I guess the point about the Elcon having a set output regardless of input voltage is only accurate for the smaller chargers then... . and up to the output power rating of the unit.


Yep, but how could it be otherwise? A 6kW charger will only put out 6kW maximum... that's more or less understood, I figured...


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## DIYguy (Sep 18, 2008)

Tesseract said:


> Yep, but how could it be otherwise? A 6kW charger will only put out 6kW maximum... that's more or less understood, I figured...


Yep, ur right... as usual...  Thanks again.. BTW, have you started shipping that new controller yet? Also, I watched your ad on EVTV, nice.... hope that generates some more sales.


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## dtbaker (Jan 5, 2008)

as an actual point of reference. the Elcon 1500 pulls 11.5 amps or so of 110vAC from the wall when charging. I do not have a 220v outlet in garage yet, so I dunno what it will do with that...


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## Qer (May 7, 2008)

dtbaker said:


> as an actual point of reference. the Elcon 1500 pulls 11.5 amps or so of 110vAC from the wall when charging. I do not have a 220v outlet in garage yet, so I dunno what it will do with that...


11.5 * 110 = 1265 Watt which correlates pretty well to the info I've googled up about this charger. It's a 1500 Watt charger that outputs roughly 1150-1200 Watt to the batteries ([email protected], [email protected], [email protected] and so on) regardless of if it's running on 110 or 220 Vac.

I didn't know a Chinese Watt is only 0.8 US Watts...


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## dtbaker (Jan 5, 2008)

Qer said:


> I didn't know a Chinese Watt is only 0.8 US Watts...


quite clear once you know that a chinese 95% efficiency is US 80%.

Seriously... perhaps when using 220v it is able to deliver the max 1500 watt rating, I just cannot confirm as I have not run it on 220v.


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## DIYguy (Sep 18, 2008)

dtbaker said:


> quite clear once you know that a chinese 95% efficiency is US 80%.
> 
> Seriously... perhaps when using 220v it is able to deliver the max 1500 watt rating, I just cannot confirm as I have not run it on 220v.


Dan,
Check your line voltage.... if it is say 120VAC instead of 110.... that would increase the efficiency to 92% or so. Stated efficiency of this charger is 94% I think....

Edit,...looked it up.. Full load efficiency is = > 93%


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## dtbaker (Jan 5, 2008)

DIYguy said:


> Dan,
> Check your line voltage.... if it is say 120VAC instead of 110.... that would increase the efficiency to 92% or so. Stated efficiency of this charger is 94% I think....
> 
> Edit,...looked it up.. Full load efficiency is = > 93%


interesting thing is at NO load the kill-a-watt meter shows 119.5-119.8 at the outlet, but when charger was charging the meter at the outlet showed significantly lower. I dunno if the charger limits what goes in, or what...

I don't have the pack in series at the moment, so I can't plug it in to get an exact number.

I still have the pack in parallel (with no charger), and it has settled to 3.67-3.68 on all cells.


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## Sun Motors (Aug 10, 2010)

Is there a product that measures amp hours or watt hours, like a kill-a-watt meter, but has a cut-off switch that can be dialed in to shut off the charger when the number of amp hours has been reached?

Then someone could just read off the amp hour count down from the instruments and set the kill-a-charger to replace the amount used.

I was just working on a good timer cut-off switch to put upstream of the charger but dialing in the amp hours to be replaced would be better.


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## EVfun (Mar 14, 2010)

dtbaker said:


> interesting thing is at NO load the kill-a-watt meter shows 119.5-119.8 at the outlet, but when charger was charging the meter at the outlet showed significantly lower. I dunno if the charger limits what goes in, or what...


That sounds like resistive losses in your house wiring. If you subtract the AC outlet voltage while charging from the AC outlet voltage when the charger is off and multiply that voltage drop by the charging AC current you will know the watts being lost in the wiring up to the charger.


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## dtbaker (Jan 5, 2008)

Sun Motors said:


> Is there a product that measures amp hours or watt hours, like a kill-a-watt meter, but has a cut-off switch that can be dialed in to shut off the charger when the number of amp hours has been reached?
> 
> Then someone could just read off the amp hour count down from the instruments and set the kill-a-charger to replace the amount used.
> 
> I was just working on a good timer cut-off switch to put upstream of the charger but dialing in the amp hours to be replaced would be better.


I would say there is no need to get that fancy with shunt or Hall effect built into a timer and relay to measure amps in. 

A quick check with your car instrumentation should show the actual amps making it to the batteries during the CA part of the charge if the meter leads are upstream from the charger, and simple math for the number of hours to replace what you need would be the conservative time limit as a backup most likely catching the charge during the CV stage as the amps slow down.....

Best case I am willing to trust my charger, but an easy backup is the charger AC input on a simple timer if it 'should' finish in the middle of the night.


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## Sun Motors (Aug 10, 2010)

Yes, a timer shut off would be the easiest way to go for the main charger shut-off. Just see the charger is putting out say 12 amps and figure the time to run it to replace the 80 aH just used in the drive.

What would be the dum-dum turn-key ideal is to have the instrument amp hours used reading after each drive communicate this amount to the charger to replace it exactly and then shut off. Just connect and hit a charge button.

I find the voltage adjustment on the Rusco 30a charger not fine enough to reliably shut the charger off. The pack voltage also varies too much with temperature to make this adjustment an accurate charger shut-off.

I do have 7 cell-logs that have nicely adjustable high and low voltage alarms. The HV alarms are wired to shut off the charger at any cell reaching 3.6v. I would prefer this to be a redundant switch, however.


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## dtbaker (Jan 5, 2008)

Sun Motors said:


> I do have 7 cell-logs that have nicely adjustable high and low voltage alarms. The HV alarms are wired to shut off the charger at any cell reaching 3.6v.


this is the key to the original idea of the thread.... wishing there is a simple inexpensive way to have cell-level HV monitoring shut down the charger in case of unbalanced cells. I think that if the cost of a black box with 50 or so input leads capable of cutting AC input power to the charger if any cell hit some safe value (over the normal stop, like 3.80v) could be made for $200 or less it would sell like hotcakes.


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## major (Apr 4, 2008)

dtbaker said:


> this is the key to the original idea of the thread.... wishing there is a simple inexpensive way to have cell-level HV monitoring shut down the charger in case of unbalanced cells. I think that if the cost of a black box with 50 or so input leads capable of cutting AC input power to the charger if any cell hit some safe value (over the normal stop, like 3.80v) could be made for $200 or less it would sell like hotcakes.


Hi Dan,

I intend to do a similar thing as Sun did with the CellLog8s modules. He used 7 of those at $28 apiece. Then maybe $5-10 apiece for the plugs and wires. And then a relay board for the alarm output isolation. Depending on the # of cells, you're probably looking at $400 plus.

For not much more than that, I think you can buy some of the low end BMS systems.

I kind of favor the CellLog8s approach because I can log cell voltage profiles. But they do present some difficulty in the system like drawing unequal self power from the monitored cells therefore causing eventual imbalance if left continually connected in the system. This is not uncommon for inexpensive cell or battery monitors.

Due to the fact that each cell monitor must be isolated and then compared to a set point, I think the $200 black box will be difficult to realize 

Let us know if you find one.

major


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## Overlander23 (Jun 15, 2009)

Yes, at some point the problem becomes shear number of parts. Each part may be inexpensive, but multiply anything by 50+ and it adds up (unless you're selling mass quantities). The two approaches are either, you monitor each cell individually with individual models (every component times number of monitors), or use bus monitoring of groups of cells which requires components which require higher voltage capabilities (which gets expensive).

I like the idea of a coulomb-counting trigger, though. The Xantrex LinkPro which I use, as well as gauges like Dmitri's EV Display, count amp-hours in and out. Having a version that was able to trigger a relay at a set point could act as a secondary fail-safe. It's not a perfect solution, but easier than monitoring individual cells. Or... some kind of solution that counts on coulomb flow and set pack voltage to trigger a relay...


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## Qer (May 7, 2008)

dtbaker said:


> this is the key to the original idea of the thread.... wishing there is a simple inexpensive way to have cell-level HV monitoring shut down the charger in case of unbalanced cells. I think that if the cost of a black box with 50 or so input leads capable of cutting AC input power to the charger if any cell hit some safe value (over the normal stop, like 3.80v) could be made for $200 or less it would sell like hotcakes.


Price, performance, reliability. Choose two. If you want it for $200 you'll either have a system that charges at snails pace or you'll find yourself being a member of the "Hardware of the month"-club.

Either way, keep the ICE as backup.


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## EVfun (Mar 14, 2010)

Here is an off the top of head quick battery monitor. It has no regulation function; it just turns the LED of an optical isolator on at about 2.5 volts and off again at about 4.0 volts. Both set points are adjustable by changing the values of R1, R2, and R3. In fact, I'm sure the current values would be a little off but are handy for showing the theory. The point of this simple idea is to use a small number of cheap parts so the per cell cost is low. You should be able to put these at each cell and wire the isolated outputs (not shown, the other half of O1) in series, the power them by low current from the vehicles 12 volt system to detect a single low or high cell. This way there would be no pack voltage spaghetti running back to a central system but the charger could be turned off if any cell got to high. This is also useful turn turn the controller down or off if any cell gets to low. 


```
R4    O1// 
+ ----^^^---->|--
    |     |     |
    >     |-^^^-|
 R1 >     | R5  |
    >     |    --
    |-----)----/\
    >     |   D2|
 R2 >     |     |
    >    --     |
    |----/\     |
    >   D1|     |
 R3 >     |     |
    >     |     |
    |     |     |
- ---------------
```
U1, U2 = TLV431 (programable zener with a 1.25 volt reference)
01 = the LED of the optical isolator of choice, photoFET unit will allow more units in series
R1 = 2100 ohm
R2 = 750 ohm
R3 = 1300 ohm
R4 = 1000 ohms (actual value depends on chosen O1, should be as high as practical)
R5 = 10k ohm

Basic (theoretical) operation:
R1 forms a voltage divider with R2 plus R3 so D2 reaches the turn on reference voltage when the cell is at about 2.5 volts. R4 limits the current to the LED of the optical isolator. You want this current to be as low as possible for reliable operation of O1 because it is normally on. R1 plus R2 form a voltage divider with R3 so that at 4.0 volts the reference of D1 reaches the turn on voltage and shunts to ground the current that was turning O1 on. R5 makes sure that O1 is completely off when D2 is off (likely not needed.)


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## Sun Motors (Aug 10, 2010)

dtbaker said:


> this is the key to the original idea of the thread.... wishing there is a simple inexpensive way to have cell-level HV monitoring shut down the charger in case of unbalanced cells. I think that if the cost of a black box with 50 or so input leads capable of cutting AC input power to the charger if any cell hit some safe value (over the normal stop, like 3.80v) could be made for $200 or less it would sell like hotcakes.


I could have gone with the cell-log 8m's that are only $14.28 ( http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952 ) . Eight of them would cover up to 64 cells, depending on arrangement, and with wiring and fuses and switch and circuit board could be brought in for less than $300 I suppose. Less if the charger has an accessible shut-off. It does takes some time however to accomplish all the connections and physical layout. My electrical friend, Ray, made the board for me. It's called the Ray board. I think that he will put it up here if there is any interest.

It is pretty cool to see bar graphs of all the cells under loads while driving, even if they are little. Bifocals?


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## major (Apr 4, 2008)

Sun Motors said:


> I could have gone with the cell-log 8m's that are only $14.28 ( http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952 ) . Eight of them would cover up to 64 cells, depending on arrangement, and with wiring and fuses and switch and circuit board could be brought in for less than $300 I suppose. Less if the charger has an accessible shut-off. It does takes some time however to accomplish all the connections and physical layout. My electrical friend, Ray, made the board for me. It's called the Ray board. I think that he will put it up here if there is any interest.
> 
> It is pretty cool to see bar graphs of all the cells under loads while driving, even if they are little. Bifocals?


Hi Sun,

Yeah, I'd be interested to see the Ray board. There was such a relay board circuit posted a while back. I have misplaced it by now :-( I might search for it. But good to see different approaches.

Do you have a problem with the CellLogs ever-so-lightly draining cells 1 thru 6 and therefore leaving cells 7 and 8 to have higher voltage? I have been using 2 CellLogs on a 14 cell pack and over the course of a week or so, cells 7 and 14 were about 120mV higher. After that I unplug the cellLogs when I am not using or charging. Kind of a PIA. I think I saw where someone had figured out how to add a resistor inside the CellLog to stop this problem. I might try that.

Regards and Merry Christmas, 

major


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## DIYguy (Sep 18, 2008)

dimitri said:


> Having BMS modules on some cells and not others is a bad idea. Parasitic loads of even a few milliamps on cells with BMS modules will cause a long term imbalance and will create more problems than it would solve. All cells in the pack must have same parasitic loads or none at all.
> 
> Even 1 mA load on a cell will eat 1AH in just 40 days.


Does the MiniBMS Centralized Master board draw only power from the 12V accessory battery? Is there any load at all on the cells being monitored? (I assume not...but couldn't find this tidbit anywhere).

Thanks.


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## dimitri (May 16, 2008)

DIYguy said:


> Does the MiniBMS Centralized Master board draw only power from the 12V accessory battery? Is there any load at all on the cells being monitored? (I assume not...but couldn't find this tidbit anywhere).
> 
> Thanks.


12V powers head end controller, while each cell powers its own module. Its the same principle regardless of Centralized vs. Distributed.


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## icec0o1 (Sep 3, 2009)

Bottom balance + HVC charger would be the way to go. That way when you discharge your pack, all cells reach bottom at the same time and you get no power, as opposed to having power and forcing one cell to go into reverse polarity or just killing it. 

So how about, to save on parts count, the charger has only one high voltage measuring circuit with a chip controlling 50 mosfets alternating between all of the batteries?


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## DIYguy (Sep 18, 2008)

icec0o1 said:


> Bottom balance + HVC charger would be the way to go.


Yes, this is what I would like to do.


icec0o1 said:


> So how about, to save on parts count, the charger has only one high voltage measuring circuit with a chip controlling 50 mosfets alternating between all of the batteries?


yes, something like this sounds good. Except I don't know electronics very well.


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## Sun Motors (Aug 10, 2010)

major said:


> Hi Sun,
> 
> Yeah, I'd be interested to see the Ray board. There was such a relay board circuit posted a while back. I have misplaced it by now :-( I might search for it. But good to see different approaches.
> 
> Do you have a problem with the CellLogs ever-so-lightly draining cells 1 thru 6 and therefore leaving cells 7 and 8 to have higher voltage? I have been using 2 CellLogs on a 14 cell pack and over the course of a week or so, cells 7 and 14 were about 120mV higher. After that I unplug the cellLogs when I am not using or charging. Kind of a PIA. I think I saw where someone had figured out how to add a resistor inside the CellLog to stop this problem. I might try that.



Greetings Major,

Sorry for the delay, Ray must be on vacation or something and hasn't got back to me yet.

I have the same small drain on all the cells so I don't have any unbalancing problems from this source.

Happy New Year,
Tom N


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## DIYguy (Sep 18, 2008)

I would be interested in the ability to monitor a "representative group" for the pack. Maybe 3 to 6 cells. After getting to know your pack, you could pick which ones win the race to the top...as long as you could use a circuit powered from the 12 volt battery and not have a parasitic load on any cells in the pack... it should work pretty well I would think. Thoughts?


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## Tahoe Tim (Feb 20, 2010)

Dang! You caught me. I am going to play with my calbs by treating them as 12 groups of 12 volt batteries. I have even been discussing 12 volt multi-bank chargers off line with a reputable member here. 

Is this what you were thinking?


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## DIYguy (Sep 18, 2008)

Tahoe Tim said:


> Dang! You caught me. I am going to play with my calbs by treating them as 12 groups of 12 volt batteries. I have even been discussing 12 volt multi-bank chargers off line with a reputable member here.
> 
> Is this what you were thinking?


Hahaha... no, actually not. But don't let me stop you. 
My current plans (which may change) is to bottom balance and hopefully use the monitoring of a chosen few cells to tell my charger it's time to stop. I will have some reduncancy here either with an Ah counter...or worst case, a timer. I plan to stay away from the top and bottom as much as possible.


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