Testing for a Smart Charger

gdmaclew

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How can I tell whether a charger is a "smart" charger?
Is there something I can do with a volt meter/ammeter to indicate if the charger is cutting off the current or going into trickle charge mode when the battery is fully charged?
Thank you.
 

Eximo

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Depends on the battery chemistry.

By design pretty much all Lithium chargers have to be smart to detect the so called knee in the charging curve. Charging beyond that point will result in thermal runaway and a fire.

Lead Acid can be dumb, but it is rare these days. Most will have a full manual mode though that you can get in trouble with, but is sometimes necessary to get a dead battery recognizable to a charging circuit as good. I would say your easiest test there would be voltage. If it charges at 15V and then ramps down toward ~13 when the battery is charged it will switch to a trickle mode. I suppose you could set up an Ammeter, but it would have to be a pretty high rated one to handle 12V charging currents

Older NiCAD and NiMH are dumb chargers I believe. Not 100% sure. They just have a target voltage controlled by a simple transistor circuit. Newer ones, not sure, been a while since I bought any.
 

gdmaclew

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Thanks.
It is a 36V Li Ion battery from my father's electric mobility scooter
.
The charger says 42V 1.8 A.

If I put a capable digital ammeter in series with the charging circuit, should the amperage drop if it is a "smart" charger when the battery is fully charged?
The indicator light on the charger goes from red while charging to green when the battery is full. It is also green when the charger is plugged into the wall but not into the battery.

The manufacturer is telling me that despite the $119 cost of the charger and $900 cost of the battery, the charger is not smart and should not be kept plugged into the battery for an extended period of time (say overnight) when it is fully charged.


Seems very strange to me.
 

Eximo

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Lithium batteries don't really discharge on their own, so in some sense unplugging it is best. But it is likely to have a parasitic drain coming from the scooter itself, and it could be offset by leaving the charger plugged in. I don't believe the manufacturer in this case.

Either the brains of the operation is in the charger, or the scooter has a simple battery management system. Measuring the current would be a pretty surefire way to see if it slows down.

Do you happen to know if the batteries are Li-Ion or LiFePO4? If you can see and count the cells, there should be 15/16 LiFePO or about 12 for Lithium Ion. LiFePO are less power dense, but far safer.

Does the charger look like this:

https://www.amazon.com/Wyness-Battery-Charger-100-240V-Electric/dp/B01MZAAZJG

Inside the brick is going to be a transformer, a big capacitor, a regulating IC for the charging, and its accompanying components. $17.99 for above seems pretty cheap, but the bill of materials in bulk is probably about half that. I see a few slightly cheaper as well. I can see this working fairly well if the safety circuits are in the battery pack.
 

gdmaclew

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I don't think there is any parasitic drain in the scooter.

The batteries are Li-Ion. I can't count the cells without ripping it open.

The battery cord end is an RCA. Center positive.

Here it is...

https://ebikeling.com/products/36v-ebike-li-ion-battery-charger

They do say...

Do not leave the battery on the charger for long periods like several days or more.

So I would think that overnight once in a while is OK. Still testing it with my multimeter.

Edit: I just finished testing and when the light on the charger turns green signalling fully charged, the current drops from 2A to 2ma.
So it looks like it is smart after all to some extent.
 
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Eximo

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I wonder if that is just an abundance of caution to avoid lawsuits or clinging to older battery types.

The times I've heard people talk about or ask about battery memory problems with Lithium...
 

gdmaclew

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Could be.

Li-Ion batteries should not have a problem with memory.

I can leave my laptop attached to it's charger indefinitely.
I have ear pods that can be left attached to its charger.
I have a Samsung smartphone that can remain attached to its charger overnight with no ill effects.
My cordless phone sits in its cradle when not being used, charging as necessary.
I have a RayOVac AA/AAA battery charger that I use to charge my Lithium Ion batteries that cost $30 and it is a smart charger.
I have a Canadian Tire 12V battery booster that weighs 5 pounds and I can leave it plugged in at all times and it will stop charging when full.
I also have a 20V Li-Ion battery pack for my cordless dril that I keep plugged in in my workshop.
I also have a 20V battery pack for my Black&Decker weed wacker and leaf blower that I keep plugged in all the time in the garage (except when it's cold - but then it won't let it charge when it's too cold)

That $900 battery cost $350 last year so maybe they are having production problems or are taking advantage of Covid.
 

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