LiPo Mfgs. Moving Toward Charging Safety Circuits? - RC Groups
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Sep 16, 2003, 03:11 PM
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LiPo Mfgs. Moving Toward Charging Safety Circuits?

"Perhaps you could point us to your other helpful posts making this suggestion for balancing circuits of other manufacturers? I would like to see their response to your suggestion.


Actually, Daren, safety circuitry originated with several of our members, and some of the manufacturers themselves, not me, so It hasn't been a response to anything I initiated.

The closest to the kind of response I believe you have in mind came from JJ Hong (Kokam):

RD Blakeslee - Senior Member

Registered: Jan 2002

Mr. JJ Hong,

On another forum, you mentioned a safety charging circuit which Kokam is testing and which you hoped to market, non-profit, @ $1.50.

Lithium Polymer cells are rapidly filling the marketplace, and instances of disastrous fires are seen more and more frequently, often caused by mistakes or lack of knowledge on the part of LiPo users .

Most of these fires have occurred during charging. Can you tell us when the safety charging circuit might be available?

Thank you,

- RD

JJ HONG - Senior Member

Registered: Dec 2002 - Location: KOREA

"…we made this circuit several times but during the field test we found spark voltage from old style of nicd charger.This spark peaked more than 50v suddenly.This is very hard to protect with economic scale element.we try again this week finally.
The price you mentioned is for normal pcm of mobile phone.we will launch anyhow soon in the market for the safety.

another method is under patent application.It will also be applied soon…"

The above exchange came after the following from Mr. Hong, over a year earlier:

Again, from ls perkins thread:


very good news for safety guard
we finished overcharge protection device for pack. when the charger or e-flyer makes mistakes to select the wrong current or max voltage,this device will stop charging and warning by sound.

This device shall be connected inbetween charger and battery pack.also we can find which charger is bad or good easily.

proto type is tested well today and finished plastic case.The price shall not be expensive.there are 6 types ., for one cell/2 serial connection/3 serial/4 serial/5 serial/6 serial.It is only depend on serial connections.very good device for you to sleep well during charging. when you finish the charging,this device will be still connected with charger.

The name will be 'KOKAM SAFETY GUARD"



Before the advent of LiPos on our scene, isperkins disclosed (with photos) how he charged his Qualcom metal-clad Lithium Ion cells through the Qualcom safety circuit board, which he detached before flying the cells. Later, perkins advocated safety charging circuitry in his seminal thread.

Troy (now B-P-P) independently tested Kokams early on, and was the first that I know of to report a LiPo meltdown (again, early in the lsperkins thead - anybody who hasn't read that thread in its entirety - it's very long - is missing a chance to know the early history of LiPos in aeroflight, and gain valuable background and insight).

Very recently, Emory Donaldson (Duralite) stated: "We have known from the beginning that the only safe way to present this technology to the hobby was to supply batteries with protection in the pack to prevent overcharge (voltage). This is the only sure way to protect the end user during the charging cycle. The only draw back is the cost of the safety circuit and its weight (3 to 4 grams), a small price to pay for the piece of mind that you eliminate the possibility of a catastrophic failure during charging. Yes, we include this protection in our packs and now many of the other major hobby battery suppliers are evaluating ways to include this safety circuit. All of us make every effort to supply a safe charger for the Lithium batteries but for many reasons it’s not always sufficient protection. Taking a chance that something won’t go wrong is a bad philosophy."


- RD
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Sep 16, 2003, 04:00 PM
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Daren's Avatar
Thanks for posting this information. I think its better presented as a stand alone rather than buried in another thread.

Sep 20, 2003, 07:47 AM
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In view of recent fires, bump
Sep 20, 2003, 10:37 AM
Little Bo's Lab
m4tm's Avatar


It appears that one Battery Manufacturer "KOKAM" is getting serious about safety, they will be selling a Safety Guard for there Li Pos!!!!!!!!!!...Has anyone heard anything from ETEC and Thunder Power???

Sep 20, 2003, 10:56 AM
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Mike, Kokam and Thunder Power have been talking about introducing safety circuit boards for at least several months. E-Tec may have, but I don't recall any specifics.
Sep 20, 2003, 11:02 AM
Registered User

FMA is serious 'bout safety

I just went to their site and clicked on the Kokam page and got a popup headed with
Safety precautions
for Lithium Polymer and NiCd cells/packs stocked by FMA Direct "

Now that's a responsible action, isn't it?

Sep 20, 2003, 11:51 AM
I plant balsa sticks too
luc's Avatar
All the manufacturers are serious about safety. On TP site, you will see a lot of info on charging, wiring in serie; they just developed new chargers, to be sold in october...
But mistakes or abuse by some is inevitable....
Another issue will be degradation by time, even if the packs were taken care of. Then imbalance may come, puffing, or worse. We should soon see that kind of problem too.
Oct 01, 2003, 07:17 AM
Registered User

Kokam acts responsibly

Joining Duralite, Kokam is now coming out with LiPo safety circuitry

JJ Hong (kokam) says: "We believe that without protecting users from the danger of using lipos no maker will survive in the market."

It will be interesting to see if Thunder Power can maintain its position that it has never had a pack go out of balance, and the safety problem is caused by bad chargers.

ETech has not been heard from, to my knowledge.

- RD
Oct 01, 2003, 01:38 PM
Registered User
landru's Avatar

Cell balancing PCM from Thunder Power

The Thunder Power website shows that they will soon be selling "Cell Balancing Units" for 3s and 4s packs. There doesn't seem to be any more info available on these units on the TP website. Price is listed at $25 for one 3s unit.

Here's a link to the Thunder Power website . Scroll to the very bottom of the webpage to see the listing.

Does anyone know more about these TP cell-balancing units?
Oct 01, 2003, 05:44 PM
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vintage1's Avatar
What worries me about all this, that anything that goes between the charger and teh pack, simply ought to be in teh charger in teh first place, and anything that goes between the pack and the connector is going to waste power when used to power the plane.

In short, I can see why Kokam etc would be haopoy to both sell extra kit and make people feel safer about charging this stuff, but I don't see that it really solves the basic problem.

That is, if anything goes wrong anywhere, you have a hot fire on your hands.

"Gee, I had the protector on, but I had it and the charger set for 5s1p when I put my 2s3p pack on and it blew up."

Oct 01, 2003, 06:48 PM
Registered User
landru's Avatar

Speaking of safety devices

Remember the surplus li-ion Qualcomm cel phone packs back from the pre-lipoly days? As I recall, those packs had a very effective charge/discharge protection pcb bulit right into them: temperature monitoring, cell balancing, over-charge and over-discharge cut-off.

Granted there were some problems with those little circuits when used for RC flying -- the hard cutoff under discharge, for instance. However it was a simple matter to remove the circuitry from the pack and use it for charging safety only; all that was required was a tap line to the connections between cell in series in the pack. I'd happily modify my existing lipoly packs to use such a charge protection circuit in series beween my charger and packs. Sure, ideally such protection would be built into the charger and or packs already. But as all lipoly vendors take pains to tell us, using these batteries for RC flying is still experimental.