Was talking to AI and he/she/they said that this product can be programmed, then used to cutoff charge reliably and not used when you want to balance charge.
Less than 11 dollars on amazon. Use phone to program. I would include detailed programming instructions, but simply ask AI.
My prebuilt 7s junk came with junk 40 watt chargers which well exceeded the 29.4v max voltage of a 7S battery, and the red light turned green when amps tapered from 0.33 to 0.32, but the charger did not shut off, and amps would keep tapering towards zero, or until one cell group touched 4.25v, then the bms HVD would shut it off.
So it would happily overcharge.
Another 7s1p prebuilt I had did not have the Diode on the BMS, it would read battery voltage on the charge port, but had the same charger. with a 30V+ OCV.
That one would happily charge to above 29.4 pack voltage until the BMS tripped, and I measured 29.6 or 29.7v on a battery which should never be charged above 29.4v.
The 7s2p prebuilt battery had a BMS that was a separate port, with a 0.4v dropping Diode,( reads no voltage at charge port) so the junk charger’s ~30.3v open circuit ouptut was reduced to 29.9v or so, but still over the 29.4v of 7S.
I used an XL4005 CC/CV bucker on the output of these 40 watt chargers to limit output voltage to 29.4v or less, and could also clamp max charge current down as far as I wanted too.
I rebuilt that 7s2p prebuilt battery that has the separate port BMS on it, as the 14 DMEGC 20P cells were all still excellent balance after a few hundred cycles, despite the narrow(8mm) thin(0.12mm) nickel plated steel busbars the factory used. It now has 30mm wide 0.2mm copper busbars :).
I don’t use buckers for charging my 7s or 10S batteries anymore, I use boosters from a 4S1P Lifepo4(12.8v nominal), and I set the booster output voltage to 41v for 10S and 28.7v for 7s and will spin the current potentiometer as high as needed but as low as possible.
I only set the boosters to 4.2 volts per cell when I want absolute maximum range, and when I do that I am usually hovering and pull the plug when amps taper to 0.2 amps, but my inline wattmeter tends to read low in this zone so actual amps are likely about 0.3 to 0.4, So 99.5% charged rather than 100%. Good enough.
Anyway you seem to want to be able to charge to under 100% state of charge and there is a simple inexpensive solution. A properly rated voltage bucker on the charger’s output.
I have this one with a 12-90vdc input range and a 1.5v to 90v output. It claims to be able to clamp output current to 0.3 amps but mine cannot go that low.
Your linked device cutting AC power to the charger when its amp draw declines to a certain amount is interesting, but your AC/DC charger might present a parastic draw on the battery when it’s AC source is removed.
So wire that in fulltime, tune it and turn it up to balance charge?
What is the diff with turned off charger cut off and the green light lit plugged charger?
Also, is a buck converter stable?
There is a certain amount of headroom required. If charger output is 42v then it might have to buck to no higher than 40.7v. I will check mine, and report back. I can only check to/from 42V.
As far as stable goes, I don’t have an oscilloscope.
Mine on my inline wattmeters has stable output voltage it doesn’t bounce around that i have noticed in my use.
Ai said it is smarter than you. It said buck converter is not as safe as smart plug. BUT it backed up your contention that a still plugged up charger will slowly drain battery.
What This Means in Real Time
While that milliamp draw sounds tiny, an electric skateboard battery left connected to an unpowered charger will experience a noticeable drop over days and weeks:
In 24 Hours: It will drain about 0.1 to 0.7 Ah from your pack. If your board has a standard 10 Ah battery, you will lose 1% to 7% of your total charge just sitting overnight.
In 1 Week: It can pull 1.5 to 5.0 Ah. This will comfortably strip away 20% to 50% of your board’s total capacity.
In 2 to 3 Weeks: The unpowered charger will completely drain the battery to 0%, bypassing the smart plug’s purpose entirely and actively risking permanent battery damage.
The Verdict
Leaving it plugged in for 2 to 3 hours after the smart plug cuts off is perfectly safe and won’t noticeably impact your range. Leaving it plugged in all weekend or during a vacation will result in a dead, unbalanced, or permanently ruined battery pack.
Switch to a smart BMS and set the charge cutoff in the app.
Or buy a high voltage power supply and set it to the voltage that is about 80% and leave it plugged in.
There is no guarantee that your charger will present a parasitic draw to the battery if it loses AC input voltage.
I mentioned it was a possibity.
There is no guarantee your charge port would allow discharging though it. One of my prebuilts would not, the other would.
Does your charge port show voltage? Please do not short out your charge port trying to determine this Hopefully it is fused, if you do.
The A eye ‘safety’ argument could be entirely human error related.
Meaning Dumbass A, didn’t set the output voltage correctly, which allowed overcharge despite undercharge being the goal.
This is unlikely if one is using the correct voltage charger for their battery.
But, A dumbass might think with a bucker on the output they can use a 20S charger on a 14S battery and just spin a few potentiometers after everything is hooked up, instead of before hooking up the load.
Never underestimate human dumbassery.
But safety could also certainly mean that the bucker failed and caught fire to Dumbass A’s home.
or,
It could mean Dumbass B hooked it up backwards and released its magic stink, but no smoke, and no fire. ( I am Dumbass B)
But As Dumbass B I have busted out the replacement Bucker anyway, to check its headroom.
I plugged it into a 39.3v 10S battery and dialed the voltage potentiometer output all the way up.
it stopped rising at 37.19v. This is with only the 0.04 amp load of my inline wattmeter.
My DMM on bucker terminals confirmed this voltage spread.
I thought my other handy 10S battery was stored at 34.5 volts, but it too is at 39 volts, So I cant presently apply a load to the bucker to check how much that 2.1v headroom falls, but it is safe to presume that at 2 amps it would be below 37.19v. and more than 2.1 volts difference between input and output.
Therefore, this bucker the one I linked in post 2 has an overhead minimum of 2.11 volts, at least in teh 39 volt range, with minimal load. This could be different at higher or lower voltages.
But I am going to use it to bring both these 10s batteries down to storage voltage by powering some 12v Fans for several hours, as I do not expect to use them as range extenders anytime soon.
As far as using this particular booster on the output of the contemptible red light green light 7S and 10S AC/DC ‘chargers’ out in my garage with their cords cut off and masking tape with skull and crossbones written all over them, Ain’t gonna happen.