2 chargers in parallel?

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elzair
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2 chargers in parallel?

Hey guys :)

I own one of these XM-3500-like OEM models with 20 x TS40Ah cells.
Since I like riding this scooter a lot, I had the idea to buy a second Thundersky charger, add another connector and charge with 20Amps in only 2hrs instead of 4hrs. -> More miles a day :D

Can I do this to the chargers? Or has maybe even one of you done this before?
My plan is to hook up both chargers for <2hrs and then let one of them do the end of charge on its own.

So?

Iccarus
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Re: 2 chargers in parallel?

I don't see why you can't do that. But don't go by me, do a little research first. In fact I've got two extra 10 amp chargers for the XM3500li since I upgraded to 24cells and a 15 amp 72v charger. Let me know if you are interested I'll give you a good deal.

2008 XM3500li Mods/Kelly KBL12251/84v 28cell 40AH pack/ Variable regen brake trigger on left brake handle/Givi/Cycle Analyst/Homemade BMS

KMX Typhoon Home build (recumbent pedelec) with two Astro Brushless 3220motors/twin castle Phoenix ICEHV 160/ Cycl

antiscab
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Re: 2 chargers in parallel?

charging at 20A (with two chargers) is fine.
If you do it on *every* charge, service life will be reduced slightly, but the cells will take faster bulk charging.
I assume you have a BMS fitted to signal charge slow down when a single cell gets high?

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

elzair
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Re: 2 chargers in parallel?

Thanks for your answers!

I´ve got a "single-cell-balancer" mounted on top of each cell and they kick in at 3,65V and draw about 1,5A. A simple overvoltage protection.

This is enough for 10A charging (...at least at the moment, don´t know how the cells are drifting in 2 years).
20A seems too much for those 1,5A shunts and that´s the reason why I wanna turn off the 2nd charger at the end of charge.

garygid
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Re: 2 chargers in parallel?

A am an EE, and ...
It is NOT a sure thing that running the two TS chargers in parallel will be OK.

These are not normal simple chargers. It is quite possible that the ThunderSky chargers, being "smart" chargers that stop charging every so often to see how the pack is doing, will NOT tolerate being run in parallel.
It could even blow up one or both chargers, cause a fire, etc.

Better to contact ThunderSky and see what their answer is to your "Is it safe to do this?" question. I suspect that they will say NO. At the least, it would be likley to void your charger and battery warranty.

However, if you try it, you will know more, but at least you WERE WARNED.

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

Iccarus
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Re: 2 chargers in parallel?

I bet at the end of charge only one charger will be on at a time anyway because whichever one senses low enough voltage to start charging again first, will prevent the other from coming on as soon as it starts charging. At this stage of charging the charger is only pulse charging at 2amps so your 1.5 amps shunts should be fine. Where did you get them? But I agree find out more...be carfull. You could also get 4 more cells and a 15 amp charger and be doing 48mph with a 2.67 hour charge time for about 6 or 7 hundred dollars at elite power solutions.

2008 XM3500li Mods/Kelly KBL12251/84v 28cell 40AH pack/ Variable regen brake trigger on left brake handle/Givi/Cycle Analyst/Homemade BMS

KMX Typhoon Home build (recumbent pedelec) with two Astro Brushless 3220motors/twin castle Phoenix ICEHV 160/ Cycl

antiscab
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Re: 2 chargers in parallel?

These are not normal simple chargers. It is quite possible that the ThunderSky chargers, being "smart" chargers that stop charging every so often to see how the pack is doing, will NOT tolerate being run in parallel.
It could even blow up one or both chargers, cause a fire, etc.

If the has installed a BMS, that can balance, and disconnects the charger when something goes out of bounds, its irrelevant what "smarts" the chargers have.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

elzair
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Re: 2 chargers in parallel?

Iccarus: I sent you a pm, maybe you didn´t recognize?

I bought the balancers here in germany, each for 6€ so 120€ in total. I don´t like this solution, It would be better if they were away from the battery poles. Just like that: http://visforvoltage.org/forum/4668-xm3500-bms-circuit

6-700$ is a lot. The current top speed is enough for me (72km/h, so about 44miles/hr (according to GPS)). I thought about adding a string of 20Ahs in order to increase my range, but I´m a student and you know.. the money.

Gary: What exactly can happen to the chargers? I suppose they have a protection agaisnt too much outgoing current and shut off if you shorten plus and minus.
As a consequence of that they should also shut off if a lot of current flows into the second charger?
Do they have diodes to e.g. avoid current flowing from the batteries to the charger?
I thought about contacting my dealer or Thundersky, but I´m quite shure they´ll say "defenitly not". Thats the reason I´m posting here :P

antiscab: How did the BMS know if charging "suddently stopped" and actually the chargers blow their minds out?

garygid
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Re: 2 chargers in parallel?

1. A charger design MIGHT have a lot of protection built in, but it is equally possible that it does not. So, you "assume" protection at your own risk. I have not taken one apart, do not have schematics, do not have the firmware, and do not know what options, parameters, and limits were "specified" (set) for this model.

It might not be protected against current backflow, too high of an external voltage, or reading unexpectedly-high voltages when it is doing its "measurement" cycles.

2. The TS charger, if it detects an "open circuit", seems to go into a coma (error state) and refuse to work any further (until a power-off reset). I suspect that this makes it unsuitable to work with a current-interrupting type of BMS.

So, it is NOT like a simple "power supply" type of charger.

As I said, you might blow up the charger, and/or anything it is attached to, or near.

If you think you know better, I cannot stop you. I do not know what will happen. I have not wanted to put my batteries (or charger) at risk.

If you have more information about its operation, I would be happy for you to share it.

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

elzair
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Re: 2 chargers in parallel?

Thanks for your answer.

Actually I´m not knowing much about this. I´m just asking and thinking about a good solution.

I got an answer from Thundersky and they say "according to your informtion, the maxmium output discharge current is 10A, so it is impossible for you to use this charger charge the battery with 20A charge current. "
I suppose they got me wrong. Tried it again.

Another solution might be a simple 72V / 30A power supply.

garygid
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Re: 2 chargers in parallel?

3.7v x 20 = 74 volts.

If you are trying to choose a charger to "assemble" a charging system, then you also need to consider how to do cell balancing and protect the cells from over-charging.

The selected pieces need to work together.

A great charger would be one that has a simple "current-limit" input to reduce the output current from maximum to suit the BMS's evaluation of a safe charging current, even to zero or "Off" (charging completed), as needed.

With this input (not hard to add to a current-limited power supply), the BMS could "throttle back" the charging whenever cells were getting too "full" (or too hot).

So far, I have not encountered any "charger" (power supply) with this great attribute.

If I had a schematic, I might be able to suggest a modification.

Cheers, Gary
XM-5000Li, wired for cell voltage measuring and logging.

Iccarus
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Re: 2 chargers in parallel?

Elzair, I don't know if you got my pm but that coupling for the charging plug does have a protection feature that will overheat and fail if you charge with to many amps. It only took 15 amps to melt mine. My wires get warm when I charge at 15 amps, so if you try this you better go to a heavier gage wire, or feel the wires periodically when charging. It might be better to just stick with what you have. Let us know what you do though. Education through error...you know. Good luck!

2008 XM3500li Mods/Kelly KBL12251/84v 28cell 40AH pack/ Variable regen brake trigger on left brake handle/Givi/Cycle Analyst/Homemade BMS

KMX Typhoon Home build (recumbent pedelec) with two Astro Brushless 3220motors/twin castle Phoenix ICEHV 160/ Cycl

Spaceangel
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Re: 2 chargers in parallel?

If you look under plastic cover you will see a DIODE under the IEC connector then it goes into RED + GREEN wires to battery pack. If you want to use 2 chargers just replace single diode with Duo-diode and you don't need the heat sink if current is under 5 amperes and use two IEC connectors or like me use the three prong TNC scooter.com 60 volt chargers which seem to make a better connection. I would rather keep one charger under seat and have rough ride destroy a $50.00 charger than destroy a $99.00 Alpha products charger. Some times the green light come on a few minutes early on one of the chargers but after 9 months every battery is still perfectly matched at 13.7 charged and 68.2 total.
Rusty
518-929-2018

KB1UKU

elzair
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Re: 2 chargers in parallel?

Thats a bit different in my scooter: My dealer replaced the IEC system with something better.
I removed the "long black connector" and installed anderson powerpoles because the black one got warm at just 10A.

5A is not that much for 40Ah batteries. I would charge them with 40A if I could, but a 72V 40A charger might bee too expensive, heavy and unhandy.
OK, 10A+5A is better than just 10A..

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