Smoke said:
The idea of series connecting several switching power supplies seems pretty sketchy.
One thing I have been looking in to for a lower wattage charger is a 24v unregulated or switching power supply with a boost mode MPPT solar charge controller.
Some of the Chinese solar charge controllers are very cheap but they have all of the programmable charging ramps and regulation for different battery chemistries and whatever series connection you have between the supply voltage and charge controller max voltage.
It's pretty easy to put together something with 400 watt programmable output for around $50.
Higher power is just more expensive. Voltage over 72v or 80v is less common and I think it's for safety reasons or certification like CE or UL.
For balance charging, an ISDT T8 charger with a 1,000+ watt 24v power supply can be had for probably under $150 but it's limited to S8 battery configuration. I think it's probably better to do something like put three S8 batteries in series to make a 24S configuration but wire it parallel for charging. The only issue is that when you do the parallel connection with +/- and balance wires, there could be lots of current flow unless it's limited in some way.
The other option is to build a BMS in to your battery pack and let it balance for you.
This is about EV chargers, not solar stuff. I don't care about solar stuff and it's off topic.
It's not...I've been doing it for many years.
You absolutely need PSU's that have fully isolated outputs.
If your PSU has a common ground or neutral from AC input to DC output, this will NOT work and will create an electrical short.
Fortunately isolated output PSU's are VERY common.
Any Meanwell will have isolated outputs. Any laptop PSU will have isolated outputs. Typical ATX PC PSU's commonly have fully isolated outputs.
Connecting the outputs in series is very safe IF they are fully isolated from the AC input.
My low voltage EV runs at 66v. I've built 2 at 82 volts and the one I'm starting now will run at 131 volts. Safety is a matter of perspective. I have no issues with building at these voltages. Obviously current kills and current at higher voltage certainly kills. You can electrocute yourself and die on a car battery! Just be careful to not complete a circuit with you in the middle of it!
You are more than welcome to use your ISDT charger. Feel free to spend lots of time plugging and unplugging your pack so the ISDT can charge it. Feel free to spend all the time an energy you want on this tedious task that can be solved so easily. On my first EV, I did exactly what you are suggesting. It's fraught with opportunities to make mistakes, miss-connect things, forget to charge a pack...whatever. The baby sitting required is significant. AND you have to do it EVERY time you charge. No thanks! I'll pass.
A BMS that supports the entire pack and a charger that outputs the total voltage you need is far better. Once you get the BMS installed and tested, you leave it alone and never mess with it again other than to tweak a setting or look at pack status. The charger delivers the total voltage the pack needs to charge to 100% and the BMS handles all the balancing. The only mistake to be made is forgetting to charge when the pack gets low.
While you are still pulling your pack apart to plug it into your ISDT so you can split up that 1000 watts between multiple packs, I'll have already been charging my entire pack at 30 amps for probably 30 minutes before you ever get started. At 48v that's 1400 watts, 82v = 2500 watts, 131v = 4000 watts!!! Sorry your ISDT is NEVER going to compete!
Don't get me wrong, I have an ISDT charger and a much more capable dual channel 10S iCharger...among other RC chargers. They are just not the right tool for regularly charging my EV's.
Having personally done what you are suggesting is doable, but I REALLY do NOT recommend doing it.
I guess whatever your expectations are plays into this.
1. I want hassle free reliability and repeatability.
2. I want something that is going to take care of itself without me watching it all the time.
3. I get tired, make mistakes, get distracted, this is "being human" and a recipe for disaster with high current batteries.
4. I want smart monitoring...aka...a smart BMS that connects to my phone is the best solution for this and works all the time.
5. I want a "fiddle free" charge solution. The BMS and big charger makes that possible and is highly reliable.
6. I obviously don't care about the cost so much. I want loads of charge current and voltage and will pay to get it.
Less common...I have to laugh! Take a wild guess how many hybrid and all electric cars are out there. Now take a wild guess what voltage they run at. Yup...380 volts is VERY common for cars. I'd call that extremely common! I think what you mean is DIY EV's or commercially made e-bikes. Especially in commercially made EV's, 36 volts is super common and of course that means lame, slow and under powered. I'm obviously not that person. If someone gave me a brand new e-bike that topped out at 25mph, I'd yawn and then immediately sell it. I do NOT want slow, lame or under powered. I build EV's that are fast, strong and NOT lame. IF I top out at 40mph, I'm disappointed. IF it takes me a minute to get there, I'm UBER disappointed. If it slows down on gentle hills, well I'm done! Where's the NOT lame EV?
My just finished 50cc sized moped build tops out at 60mph and accelerates as well as cars do. I have to say I'm disappointed. It's NOT strong enough! I'm running at 200 phase amps. I'm OK with the top speed, but it gets there much too slowly. I want it to PASS the cars, not just keep up with them! I will never get on it with it's current power plant and say to myself "OH shit that's fast!".
AKA...depends on your expectations and obviously mine are a bit higher than yours.