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Topic # 108330 28-Aug-2012 16:47 Send private message

I have bought myself a new Ryobi battery drill and found that while the charger (Li-ion) will show a green light to indicate that the battery is fully charged it doesn't turn off the charge. Instead I have to remember to unplug the charger or else risk cooking the battery. I have been getting round this with a timer at the wall plug but this means I am guessing the charge time.

Would it be an easy modification for an electronics whiz to have the charger turn off when the green light comes on? It seems strange to me that it doesn't given that the hard bit of determining whether the battery is charged has already been done.

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  Reply # 678269 28-Aug-2012 16:52 Send private message

cep32: I have bought myself a new Ryobi battery drill and found that while the charger (Li-ion) will show a green light to indicate that the battery is fully charged it doesn't turn off the charge. Instead I have to remember to unplug the charger or else risk cooking the battery. I have been getting round this with a timer at the wall plug but this means I am guessing the charge time.

Would it be an easy modification for an electronics whiz to have the charger turn off when the green light comes on? It seems strange to me that it doesn't given that the hard bit of determining whether the battery is charged has already been done.


How do you know that it is still charging? Does it have a warning in the manual that you must unplug it after a period of time. Sounds like a safety issue if it does stop charging. Sounds like it is a bottom of the range/home handyman product.

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  Reply # 678271 28-Aug-2012 17:01 Send private message

Yeah, as Mattwnz says: "How do you know it's still charging?".

I routinely leave batteries in the charger, sometimes for many days after I put them on charge, simply because the charger is in the garage, and sometimes I don't remember to check it. The batteries are not even warm when removed after several days, whereas during charging, they are noticeably warm to the touch. I have 3 x Lithium Ion One+ 18V batteries, and 2 old NiCd ones which are still going strong after 7 or 8 years of being charged in this way.





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  Reply # 678273 28-Aug-2012 17:12 Send private message

grant_k: Yeah, as Mattwnz says: "How do you know it's still charging?".

I routinely leave batteries in the charger, sometimes for many days after I put them on charge, simply because the charger is in the garage, and sometimes I don't remember to check it. The batteries are not even warm when removed after several days, whereas during charging, they are noticeably warm to the touch. I have 3 x Lithium Ion One+ 18V batteries, and 2 old NiCd ones which are still going strong after 7 or 8 years of being charged in this way.


No way would any li-ion charger "keep charging".. it probably runs a small maintenance charge to keep the battery topped off.  If it "kept charging" your li-ion battery would turn into a li-ion grenade...

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  Reply # 678295 28-Aug-2012 17:51 Send private message

If it is still charging and gets hot after 12 hours on charge, it could be faulty.

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  Reply # 678309 28-Aug-2012 18:31 Send private message

mattwnz: If it is still charging and gets hot after 12 hours on charge, it could be faulty.

I don't think that is possible with this particular charger, because it does a battery good/no good test at the start of charging and won't charge at all unless the battery passes the test.  I have had a couple of my older NiCd batteries fail in this way, after many years of use.





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  Reply # 678312 28-Aug-2012 18:56 Send private message

The first 80% of charge can be done in 1-2h, the last 20% can take an hour (in general, not this specific charger). Li-ion fast chargers will show a green light at 80% charge so you can get on with the job rather than wait an hour for only 20% extra.




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  Reply # 678391 28-Aug-2012 20:51 Send private message

The user manual has instructions to remove the battery once the green light shows that it is charged and not to leave the battery on the charger.

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  Reply # 678417 28-Aug-2012 21:29 Send private message

cep32: The user manual has instructions to remove the battery once the green light shows that it is charged and not to leave the battery on the charger.

I would take out back ROI where you got it from. Take the battery and charger.
If it's getting hot (too hot) you don't want it at your property. Take it in and get the supplier to check it out give you an explanation that satisfies you that it's ok.

Properly managed you can recharge Li-ion in under an hour...... But you have to monitor battery temperature and voltage, and control the charge current.

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  Reply # 678437 28-Aug-2012 21:46 Send private message

The user manual is written for Ni-based batteries and just got copied for Li-based batteries. It is a design requirement that charge is terminated when either the charge current drops to below about 10% of initial current, or a timeout. It is a matter of safety. The instruction to remove from charge is just in case both the charger and the battery internal protection circuit fails, to protect the manufacturer from a claim.

You will be amazed of safety issues around any battery. Alkaline for instance constantly produces hydrogen (while used) and a huge amount of it. Ni-based batteries produce some hydrogen when fully charged. All Li-based rechargeable batteries (except LiFePO4) have exothermic reactions when they fail. Then there are regulations around freight safety, including the number of cells that can be shipped with a product. Those paper tabs you pull out to connect a battery that is already inserted in a battery compartment is not for convenience, it is because a product cannot be shipped with the battery connected.




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  Reply # 678845 29-Aug-2012 16:53 Send private message

cep32: The user manual has instructions to remove the battery once the green light shows that it is charged and not to leave the battery on the charger.


They all say that.

A Li-ion is considered charged when the constant voltage part of the charge drops to 10% of the current that you were putting in during the constant current part. This is one of the reasons you should never slow charge lithiums since the charger will never terminate the charge.

Since its constant voltage the chance of a BOOM is minimal, but its still not good for the cell if it never stops.

Most chargers will start to indicate green as soon as you hit the 4.2 volt constant voltage, and then the red goes out as the current drops so its almost totally green when it hits 10%, at which point it should stop.




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  Reply # 678851 29-Aug-2012 17:08 Send private message

I've got a current-model Ryobi charger here, although it's a NiCad. The green light stays on all the time, even if nothing is plugged in. The light blinks while it's charging then stays a solid green again once it's finished.

Another charger I repaired a couple of days ago does much the same thing, light goes on when it's on charge, and stays on even when it should be fully charged. I had to repair the charging unit after someone blew it by plugging an over-voltaged DC charger into it, and it does have a charge protection circuit in it, given that it's a cheap unit, I'd hope the far nicer Ryobi unit has the same.

Edit:

Ok, apparently the Ryobi unit doesn't - from the manual:

The charging procedure is not ended automatically... a temperature increase of the battery indicates that the battery is fully charged


WTF...




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  Reply # 678860 29-Aug-2012 17:28 Send private message

The nicd chargers are all junk on the ryobis I have had in the past - constant current with the limiting done in the plugpack and prone to variations in line voltage.

the one plus kit is the first stuff I have seen from them approching usable as far as the batteries go.




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  Reply # 678899 29-Aug-2012 18:54 Send private message

Ni-based batteries heat up at the end of charge because at end of charge they generate hydrogen which gets recombined into water by a tiny catalytic converter. The catalytic reaction generates heat.

All Ni-based battery manufacturers (like Panasonic, GP, Sanyo) state their batteries can safely be charged for a year without explosion or leaking, however they do not say that in overcharging them they loose capacity. A good quality charger will switch off. Ni-based batteries are also only 70% efficient (when charging) and the extra 30% you need to put into them is converted to heat (in addition to the catalytic reaction heat at end of charge).

All Li-based battery chargers must have a safety timer (except LiFePO4). This is not an option. The reason is because most of the time the battery is held above the voltage where lithium metal plating can occur (something like 3.8V) and when you have lithium metal you have a highly unstable exothermic chemical that is really hard to extinguish once it catches fire. LiFePO4 is the exception because the full charge voltage is 3.65V so always below the voltage where plating occurs, and furthermore you need over 600 deg C to break the bond with phosphor. Lithium battery charging is over 95% efficient so there is virtually no heat generated.

So, the Li-Ion charger mentioned in the OP must automatically switch off at end of charge (not necessarily the moment the green light comes on, can be an hour or two later) or else it is dangerous and should be recalled.




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  Reply # 679471 30-Aug-2012 21:27 Send private message

This is the response I just got through from Ryobi.


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  Reply # 679480 30-Aug-2012 21:44 Send private message

cep32: This is the response I just got through from Ryobi.


Too small, can't read it.




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