Repurposed classic?

Started by BlackwaterPark, February 06, 2023, 09:53:06 AM

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BlackwaterPark

so it looks like I'll be getting a hawks bay 120 soon,  and my 9 year old classic 150 will be standing in the unemployment line before too long.  But I might have a job for it.  I've been using my inverter as a ac charger on the occasions that i need it,  but it's inefficiency (~58%), coupled with its noise (think 747 on the tarmac), and the fact that it acts as charger as priority over house loads,  make this a less than ideal setup.  In my older systems,  i had always used discreet ac chargers and very much wish to go back to that setup.   Now,  Signature Solar has just come out with a 48v lithium specific dual voltage input,  adjustable voltage AND current output charger which is good for a max output of 100a dc (while running 240v into it).  This thing is $400. To my mind, that's extraordinarily cheap. Maybe too cheap to be trustworthy to not worry about my rather expensive kilovault habs getting damaged.  I've talked to Signature in the past and they have always billed their ac chargers as "bms chargers", which are essentially constant voltage power supplies, meaning they absolutely rely upon the batteries bms to throttle the chargers down.  I have spoken with kilovault tech support,  and they have informed me that it's a bad idea to constantly rely on the bms to perform this task, as over time,  it runs the risk of damaging the electronics.   Therefore,  I'm wondering how viable it is to simply run that charger through my classic 150. Any reasons why I wouldn't want to do this?
Attached is the spec sheet for that 100a charger...Chargeverter-5kW-Spec-Sheet_1.0.1 (1).pdf

BlackwaterPark

I guess I'll just run it and see then

boB

This has been done before.   

But remember that a battery or rectified AC into a charge controller starts with a very low impedance compared to a solar panel and so the max power point voltage can be very close to the open circuit voltage in that case  (Voc)

Sometimes a low-ish value power resistor is used to sort of give the Classic a buffer to work with near that input voltage.

boB
K7IQ 🌛  He/She/Me

BlackwaterPark

OK, so filtering that through my non EE brain,  I'm coming up with something along the lines of "yea, it can work,  but it's not really a very efficient way of going about it"?

boB

Yes, not the best way.  BUT what is used to charge one battery from another has the same kind of circuitry as a Classic.  A buck or boost converter. 

It's mainly the software and the resolution of the current and voltage feedback at the extreme end of that voltage curve and the small change in PWM change duty cycle necessary to change the battery output current in this scenario is what hinders this from being the best way.

If you want to try this, I would use one of the hydro modes where you can adjust the PV input voltage more precisely and not just try to track like a normal solar panel.  SOLAR mode for instance would be a bad mode to use for this.  P&O might also work ?

Adding a small resistance value power resistor to the input would also help the adjustment to be smoother.   

Charging a 12V battery from 24V battery would most likely be easier than trying to charge a 12V battery from a 48V battery, say.  Ratio of 2:1 rather than 4:1    Think of the Classic as a car transmission.  High RPM to lower RPM.  High voltage to low voltage.   

So, if you try this, let us know how it works !
K7IQ 🌛  He/She/Me