# Regarding charging LiFePo4s and the Elithion BMS



## Olaf-Lampe (Feb 24, 2010)

The Elithion BMS for LiFePO batteries has a CAN-Interface to regulate voltage and current comming from the charger. Your charger should be able to rise the voltage a bit. Also the DCDC should be able to handle 148V instead of 140V fully charged. You can plug it directly to your lead battery when the output voltage of the DCDC is regulated to 13,8V -14V. Just use a fuse between DCDC and battery.
-Olaf


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## frk2 (Jan 2, 2009)

My charger has no such CAN interface option! its a standard fixed 120v PFC charger


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## frk2 (Jan 2, 2009)

Sorry I think it DOES have a can bus - its an Elcon so it must. i guess I am OKAY then with the increased nominal voltage


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## dimitri (May 16, 2008)

frk2 said:


> Sorry I think it DOES have a can bus - its an Elcon so it must. i guess I am OKAY then with the increased nominal voltage


Just because the charger has CAN bus, it does not mean it can increase the voltage. Elcon chargers are programmed by the dealer, as far as I know, not by user. CAN bus likely just has one command "enable/disable" based on BMS signal. Check with your Elcon dealer to see what exactly your charger can or cannot do.

Also, not all Elcon chargers even have the CAN bus, some have NO/NC BMS input and some have none at all.

You can probably add one cell without any issues , but it will shift CC/CV "knee" and it will increase your charge time because of that. However, adding 2 cells will shift CC/CV "knee" too much and you will never get a fully charged pack and charger will spend too much time in CV phase, likely timing out after some time. As long as this allows your desired range, it may work for you, but it would be better to increase charger's voltage to match the pack size.

Hope this helps.


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## Guest (Apr 23, 2010)

I think the next question is can your controller handle the extra voltage? Not all can handle that extra juice and could potentially lead to letting out that magic smoke from that illusive can inside the controller. 

Pete


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## Olaf-Lampe (Feb 24, 2010)

The CAN interface from Elcon is a separate black box. It is able to 'understand' the Brusa protocol provided by Elithions BMS. We also had a Elithion flash-version that was taylormade for Elcon chargers. ( Thanks again Davide for your effort )
The charger we have is 300V nominal and has a max. voltage of ~420V. 
I expect the 120V version has a similar adjustment range. 
-Olaf


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## frk2 (Jan 2, 2009)

http://www.diyelectriccar.com/forums/showthread.php/review-chinoz-pfc-charger-38108.html

is the charger that I have. Its a Chinoz 10Amp PFC. The manual does state the Input voltage has a range of upto 170V though. The DC/DC does so likewise. Has a range of upto 165 Volts. I wonder if its a good idea to be touching these max boundaries all the time.

I was hoping from a reply from EVComponents but they themselves have had a setback!


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## frk2 (Jan 2, 2009)

maximum output voltage sorry. That would come about (on 40 cells) to 4.25VPC and in 38 cells to about 4.47VPC. Whats the max voltage the LiFepo4 cells should be?


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## Coulomb (Apr 22, 2009)

dimitri said:


> Just because the charger has CAN bus, it does not mean it can increase the voltage.


My understanding is that on the lithium versions you can set the point where the CC/CV transition happens, i.e. the maximum output voltage, in a CAN packet.

Obviously there are limits; a 120 V charger can't output 500 V (though you can ask it to). The limits all seem to be around 133% of the "nominal" voltage. So the 312 V nominal charger has a limit of 417 V. A 144 V model has a limit of 192 V, and so on.

So if the preprogrammed "curves" didn't go as high as you want, but where you want is less than the limit of the charger, then using the CAN interface could indeed "increase the voltage" of the charger. I imagine that they would have at least one "curve" that was at the limit of the charger, but who knows.

You can also program a current limit in the same packet. I've been assuming that this is the CC current limit, so if you can bypass 600 mA, you can tell the charger to limit its output to 600 mA when the first cell gets to maximum voltage.

So it looks ideal from a BMS perspective: one packet sets the maximum voltage and current, and you can adjust those limits as time goes by.


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## Olaf-Lampe (Feb 24, 2010)

Coulomb said:


> My understanding is that on the lithium versions you can set the point where the CC/CV transition happens, i.e. the maximum output voltage, in a CAN packet.
> 
> Obviously there are limits; a 120 V charger can't output 500 V (though you can ask it to). The limits all seem to be around 133% of the "nominal" voltage. So the 312 V nominal charger has a limit of 417 V. A 144 V model has a limit of 192 V, and so on.
> 
> ...


If you have an Elcon charger with a real CAN interface, there are no preprogrammed curves. There are PbA versions of the same charger with preprogrammed curves and there is ( has been? ) an intermediate version with only a BMS on/off input.
Unfortunately the charge current limit from the Elithion BMS is only adjustable in 1A steps. If you have a highvoltage charger that could deliver 5.5A you have to set the limit to 5A or get an overcurrent-error. Pretty bad IMHO, because you'll loose 10% of power. It's a handicap for balancing also 
Maybe Elithion will change that soon. 

-Olaf


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## Coulomb (Apr 22, 2009)

Olaf-Lampe said:


> If you have an Elcon charger with a real CAN interface, there are no preprogrammed curves.


Ah. I thought you could use either.



> Unfortunately the charge current limit from the Elithion BMS is only adjustable in 1A steps. If you have a highvoltage charger that could deliver 5.5A you have to set the limit to 5A or get an overcurrent-error. Pretty bad IMHO, because you'll loose 10% of power. It's a handicap for balancing also


Um, I thought it was in 0.1A increments?

[Edit: as per this page: http://lithiumate.elithion.com/php/controller_can_specs.php#ElCon_messages. And also a PDF I was sent by a vendor.]

Maybe that's only for the IEEE version; perhaps you have the version that speaks Brusa? Alas, I can't seem to find any details in the Brusa-speaking version. I like the CAN bus being at 500 kBPS, since it matches the motor controller we'll be using (but the CAN speed for the controller can surely be changed).


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## Coulomb (Apr 22, 2009)

Coulomb said:


> Um, I thought it was in 0.1A increments?


Oops, I see you are saying that this is an Elithion BMS limitation, not a charger limitation. Sorry. And also strange. Maybe they're used to lower voltage setups, where the current is larger, and so 1 A is a more usable resolution (but just barely).



> Maybe that's only for the IEEE version; perhaps you have the version that speaks Brusa?


It appears that the Brusa also specifies current (either mains current or DC output current; handy) in 100 mA units:
http://lithiumate.elithion.com/php/controller_can_specs.php#Brusa_msg


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## dtbaker (Jan 5, 2008)

frk2 said:


> maximum output voltage sorry. That would come about (on 40 cells) to 4.25VPC and in 38 cells to about 4.47VPC. Whats the max voltage the LiFepo4 cells should be?


the charge curve 'should' be set so the cells go no higher than 3.75 or 3.80 during charge if they are Thundersky I'd say... they go thermal pretty quick after that from the curves I have seen and if you have one out of balance higher than others it could be damaged before total pack voltage shuts down the charger.


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