Announcement

Collapse
No announcement yet.

Charger/Discharger all-in-one

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Charger/Discharger all-in-one

    I'm relatively new to e-bikes getting my first in March 2021. I have however a few years experience with electric model aircrafts that use the same battery technology as e-bikes for the most part. That experience has taught me the in and outs of battery maintenance for sure.

    Here is my question, why has no one developed a charger that not only charges but discharges e-bike battery packs. In fact not many have even developed chargers that can be adjusted to charge these packs to anything less than 100%, which is well known not to be good of these batteries.

    I am waiting for delivery of my new Luna 3 amp mini charger so I can at least change the charge from 100% to something lower hopefully extending the life of my 48v 17.5 aH Samsung battery pack.

    With winter coming to the Northwest I won't be riding the bike much so now I'm looking for a practical way to discharge the battery to the recommended long term storage voltage. Thus far I have been unable to find any commercially made device to accomplish this task. I may have to resort to building something myself.

    So to the product development people at Luna why not reach out to your sources of the chargers you sell to see if they can design and build for sale a standalone unit or incorporate a discharger into their various chargers?
    2021 Himiway All Terrain Cruiser

    #2
    Originally posted by hoggdoc View Post
    ...Here is my question, why has no one developed a charger that not only charges but discharges e-bike battery packs. In fact not many have even developed chargers that can be adjusted to charge these packs to anything less than 100%, which is well known not to be good of these batteries
    There are actually plenty of chargers that charge electric bike batteries to less than 100% (usually called "smart chargers" and luna has some) - just not the $15-20 ones... however I did a "poor man's smart charger" by putting a tring of diodes in series with the output and a jumper: https://electricbike.com/forum/forum...charger-reload

    The reason a charger doesn't discharge is that compared to RC batteries these have orders of magnitude more energy and to discharge in a reasonable amount of time need to dissipate at least 100-200W so your charger/discharger would be enormous and get *very*, *very* hot... I found a good load sitting around the house and described it here: https://electricbike.com/forum/forum...discharge-load



    Comment


      #3
      Originally posted by AZguy View Post

      There are actually plenty of chargers that charge electric bike batteries to less than 100% (usually called "smart chargers" and luna has some) - just not the $15-20 ones... however I did a "poor man's smart charger" by putting a tring of diodes in series with the output and a jumper: https://electricbike.com/forum/forum...charger-reload

      The reason a charger doesn't discharge is that compared to RC batteries these have orders of magnitude more energy and to discharge in a reasonable amount of time need to dissipate at least 100-200W so your charger/discharger would be enormous and get *very*, *very* hot... I found a good load sitting around the house and described it here: https://electricbike.com/forum/forum...discharge-load


      Thanks unfortunately I didn't see your response until coming across a design that uses 12v 50w halogen bulbs in series as a load for discharging 48v batteries. This configuration gives a near perfect 200w load. I will connect a meter in line with the device and battery to monitor the voltages.

      I am curious how you make the connection to the battery for discharge. My inclination is to use the connection points where the battery connects to its mounting bracket. I have discover that the flat prongs on a standard 120 volt ac plug are the proper thickness for the job and intend to cut them from the plug an solder them to the discharge device.

      I am considering using a switch to disconnect the load from the source plug to avoid sparks near the battery when connecting to discharger to the battery.

      How do you make your connections and how do you avoid the the sparks?
      2021 Himiway All Terrain Cruiser

      Comment


        #4
        Originally posted by hoggdoc View Post

        Thanks unfortunately I didn't see your response until coming across a design that uses 12v 50w halogen bulbs in series as a load for discharging 48v batteries. This configuration gives a near perfect 200w load. I will connect a meter in line with the device and battery to monitor the voltages.

        I am curious how you make the connection to the battery for discharge. My inclination is to use the connection points where the battery connects to its mounting bracket. I have discover that the flat prongs on a standard 120 volt ac plug are the proper thickness for the job and intend to cut them from the plug an solder them to the discharge device.

        I am considering using a switch to disconnect the load from the source plug to avoid sparks near the battery when connecting to discharger to the battery.

        How do you make your connections and how do you avoid the the sparks?
        I've installed XT90S connectors between batteries and the motor - I often carry two batteries (one on downtube, other on rear rack) and use the connectors to switch between - since I have a battery management unit that has a current sense shunt I've got the one that goes to the batteries between it and the batteries and I put another right near the motor to make it easy to remove the motor for service (did that when I did a relube)

        It's very important to use the "S" version of the XT90 - they come in both XT90 and XT90S. The nasty destructive sparks come from plugging in a live battery to a controller that has a lot of capacitors on the front that pretty much look like a short until they are charged. The "S" is the spark resistant - they accomplish this by having a ring in the top of the female connector that makes contact first and charges the capacitors through a small resistor.

        The XT90S's are a little more expensive but they are just a couple of dollars, much less than any switch rated for the current's/voltages and I'm dubious about lower cost switches not going south due to the sparks. If slathered up with dielectric grease they are relatively waterproof too

        Do not try to plug into a skillet load (or any other high load - controllers don't present much resistive load when plugged in, only while running)) with a hot battery though, that can fry the little resistor - better to plug the skillet in last (I use alligator clips)


        The connectors for switching between batteries all heat shrink wrapped in the two different "positions" for the different batteries:

        Click image for larger version  Name:	sw_2639.jpg Views:	0 Size:	227.7 KB ID:	144481 Click image for larger version  Name:	sw_2641.jpg Views:	0 Size:	257.5 KB ID:	144482

        Comment


        • hoggdoc
          hoggdoc commented
          Editing a comment
          Thanks for the reply. I'm curious why did you choose the XT 90 as the XT 60 at 60 A handling should be more than adequate for most installations. I have to order some S type connectors for sure, just haven't put them in stock yet. I have plenty of XT 60 left over from my RC plane and Quad flying days.

        • AZguy
          AZguy
          Giga Member
          AZguy commented
          Editing a comment
          The "common" thing with most DIY electric bike folks is to go XT60 on the charge side and XT90 on discharge - makes it so they won't get accidentally plugged in wrong... I'd bet >75% of DIY guys that are running <60A are using XT90's for discharge

          The cost delta on the XT90's is so minimal compared to the XT60's and even if "all" we are talking about is 30-45A why not get the least contact resistance we can so we don't get a weak connection that overheats

          I don't think the XT60's come in the anti-spark version and so that may be near the top of the list too
      Working...
      X