Power in Flux
Likes Likes:  2
Page 2 of 2 FirstFirst 12
Results 11 to 16 of 16

Thread: Finding High Power Lithium-ion battery Chargers

              
   
   
  1. #11
    Empulse R #24 frodus's Avatar
    Join Date
    Aug 2010
    Location
    Portland, OR
    Posts
    2,652
    Post Thanks / Like

    My Social Networking

    Follow frodus On Twitter
    I don't know, you're the one who brought up building something with Elcon flatpacs You'll have to see how they communicate. I've only worked with flatpacks you set via potentiometer. I know nothing about the ones you're considering.

    Brandon's charger has CAN, but also has a Canbus control board for it so you can adjust voltage and current setpoints. It's also 3.3kW.
    Travis

  2. #12
    Junior Member
    Join Date
    Nov 2018
    Posts
    12
    Post Thanks / Like
    Hoping I didn't make some sort of mistake in reading the listing, but after a quick ebay skim I saw 4 eltek flatpack2 1800W units for $30 each here in the states... almost 4x less than any other units I've seen since hearing about using these. Ended up springing for all 4 with the intent of a 2s2p ~7kW charger or 2 separate 3.6kW chargers that might be paired in parallel. These will be mated to 12 or 14 nissan leaf cells.

    Thanks for your explanation @Frodus- it made it much clearer how they should work.

  3. Likes Zotto liked this post
  4. #13
    Empulse R #24 frodus's Avatar
    Join Date
    Aug 2010
    Location
    Portland, OR
    Posts
    2,652
    Post Thanks / Like

    My Social Networking

    Follow frodus On Twitter
    Quote Originally Posted by jhaggerty View Post
    Hoping I didn't make some sort of mistake in reading the listing, but after a quick ebay skim I saw 4 eltek flatpack2 1800W units for $30 each here in the states... almost 4x less than any other units I've seen since hearing about using these. Ended up springing for all 4 with the intent of a 2s2p ~7kW charger or 2 separate 3.6kW chargers that might be paired in parallel. These will be mated to 12 or 14 nissan leaf cells.

    Thanks for your explanation @Frodus- it made it much clearer how they should work.
    Do you have a link for the Flatpack 1800W?

    I'd suggest that you consider using the terminology "Leaf Modules" or "Leaf Batteries". Each of those modules has 4 cells in there as a 2s2p setup. 14s is only ~51.8V Nominal. But when you say 14 modules of 2s2p, that brings it up to 28s in reality, and a Nominal voltage of 103.6V.
    Travis

  5. #14
    Junior Member
    Join Date
    Nov 2018
    Posts
    12
    Post Thanks / Like
    Yeah that was a slip up, we've been referring to them as modules when talking charging/bms/ pack voltage etc. amongst ourselves.

    Here's the link, though I bought all that were available. https://www.ebay.com/itm/362501044768 They're not the HE or S version, hence the silver front plate and low price. I haven't found a great deal of info on these ones in particular, but have found a specs sheet that talks efficiency other specs. I'm hoping they are programmable using the same communications that Remmie has used.

  6. Likes Zotto liked this post
  7. #15
    Senior Member
    Join Date
    May 2013
    Location
    Kildare, Ireland
    Posts
    281
    Post Thanks / Like
    Quote Originally Posted by Zotto View Post
    Hmm can you explain how the DC power supply clamped to Vmax would work in that case, I thought the supply voltage was supposed to float to whatever the current source from the power supply set it to, then eventually when the pack reaches ~4.2V/cell the constant voltage took over.
    Apologies for the slow reply - I see Frodus has provided a few answers already so what follows may amount to some repetition but howevenever here we go.

    CC-CV as you know means Constant Current Constant Voltage and refers to the preferred approach to charging Li-chem batteries. Put very simply, the CC amounts to the max current of the appropriate DC supply for charging the pack and is a factor of either the charge uptake constraints of the cells in use, or of the power capacity of your DC supply. The CV then (again keeping things simple) amounts to the max voltage of the DC supply.

    So now, lets examine the arbitrary case of a 10s arrangement of Leaf modules. 10s give you a VMax of 84V across the pack and 20 cells in series to monitor.
    Those modules have a nominal charge capacity of 60Ah and lets assume a max charge acceptance of ~5C meaning that you can charge them at up to 300A.
    So, at its most basic, your Charger will have a max current of 300A and a max voltage of 84V. Peak power delivery will likely occur at that 84V threshold where the cycles changes from CC-CV meaning that that power supply would be rated at somewhere in the region of 25kW (again we're just being arbitrary about things here).

    Now once the DC power supply conforms to that charge current, and that maximum voltage, then that's all that's required of it. The whole CC-CV bit actually takes care of itself and here's why:
    If you're engaged in this sort of a project in a school setting then I'm going to expect that you're familiar with Ohm's law - yes? ...and you should also certainly be familiar with Kirchhoff's laws and the idea of an 'equivalent circuit' as well .. yes?
    Well, in this case you have two components in play - you have the battery, and the charger. Each has its own resistance (in this instance most commonly referred to as its 'internal' resistance) and assuming ideal wires linking the two together then the only current limiting factors in the circuit are these resistances - agreed?

    So lets assume a circuit where the positive terminal of the DC power source is connected to the positive terminal of the battery with a switch in between, and the respective negative terminals likewise.
    Hypothetical circuit.jpg

    If we were to assume zero resistance at any point in the circuit (internal resistances included) then there would be infinite current flow arising on account of any difference in voltage between the battery and the power source - agreed?
    [I=V/R -> if R == 0 then I == inf]

    So now we introduce the resistances.
    Restistances.jpg

    So now R!=0 meaning that there is a characteristic limit to the current which will flow in the circuit for any given voltage differential between the two voltage sources. In this initial scheme lets assume were in the CC stage of the charge. Accordingly the effective resistance of R(psu) >> R(batt) as the current limit of the supply is in play. As a result if we close the switch and measure the voltage at the point between the two resistances with reference to the common line, what we will find is that the voltage at that point will be equal to the V(batt) + I*R(batt) regardless of what the design voltage of the PSU is. This happens specifically because the current limit is being enforced, and the current limit is being enforced because the battery is able to draw far more current than the PSU can produce.

    This will remain the case until such time as the sum of V(batt) + I*R(batt) becomes equal to V(psu) - I*R(psu). At this point there is no longer sufficient voltage difference between the source and the battery for the full current to be pushed through the circuit and hence the current limiting condition will cease to be in effect and the CV portion of the charge begins. From here on out, as the voltage of the battery continues to climb, the portion of the total voltage difference between the battery and the supply which is dropped across any given resistance is reduced, and so the current flowing also reduces - hence the system is self limiting and requires no further governance. Which is to say that CC-CV is far less of a strategy, and far more of a direct consequence of the application of a power source which has a fixed maximum voltage and current. (Which isn't to say that the CC-CV charging strategy isn't in fact 'a strategy', it certainly is. It's merely a happy coincidence that it's also very easily implemented)

    Quote Originally Posted by Zotto View Post
    I am designing my own BMS actually! This is for our senior design at school, the BMS design is nearly done, and should hopefully work, but I well be doing a ton of testing to ensure that it does.
    How are you defining BMS (ie: monitoring system or management system [lets try and avoid the third association. :P])


    Quote Originally Posted by jhaggerty View Post
    I’m working with Zotto on this project. I was looking at building out a charger using Elteck flat packs or similar, but where we’re running into confusion is the constant current distinction. Is it appropriate to use a power supply like the flat packs stacked in series and set to a voltage set point to charge for the CC portion of the charge cycle? We were getting confused on whether the voltage of the charger is supposed to match with the cell voltage during the CC charge cycle.
    Think the above covers that.

    Quote Originally Posted by Zotto View Post
    Hmm, that does make sense! When you say "set" these values, is it done manually, or over an I2C or CANbus? I am assuming its different for each charger solution, but I have no interest in implementing a CANbus for our electrical system, so I was hoping I could find a manual or I2C driven charger.
    Again, I think the above covers that.
    Comms need only be required for charge interruption or initiation, and even then that can be achieved with relays.
    They also permit more advance controls such as charge current derating based on pack temperature etc.. nothing you need to worry about in the school project landscape.
    Last edited by Spoonman; 17 December 2018 at 0459.

  8. #16
    Junior Member
    Join Date
    Dec 2018
    Posts
    6
    Post Thanks / Like
    Wow, that makes a ton of sense! Thanks so much!

Page 2 of 2 FirstFirst 12

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •