Using a Li_Ion charger with Ni-MH

I was wondering whether a 4.2V li-Ion charger could be used to charger 3 se ries NiMH batteries, assuming appropriate current limits where in place. I understand that they may not achieve full charge, but could be charged to

80% I think. This is because I use NiMH batteries in my product and have to design the charging circuit and there is a lot more choice in Li-ION charg ing ICs. Any thoughts would be appreciated. Steve
Reply to
steve
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series NiMH batteries, assuming appropriate current limits where in place. I understand that they may not achieve full charge, but could be charged to 80% I think. This is because I use NiMH batteries in my product and have to design the charging circuit and there is a lot more choice in Li-ION charging ICs.

If you have to ask, you shouldn't do it. If you don't have to ask, you shouldn't do it. Use the chip designed for the task.

Reply to
mike

3 series NiMH batteries, assuming appropriate current limits where in plac e. I understand that they may not achieve full charge, but could be charged to 80% I think. This is because I use NiMH batteries in my product and hav e to design the charging circuit and there is a lot more choice in Li-ION c harging ICs.

Actually, just found a TI app note that says it works well, however you onl y get around 80% of full charge though this may extend the life of the batt eries (bq24040 series)

Reply to
steve

series NiMH batteries, assuming appropriate current limits where in place. I understand that they may not achieve full charge, but could be charged to 80% I think. This is because I use NiMH batteries in my product and have to design the charging circuit and there is a lot more choice in Li-ION charging ICs.

What about using LSD-NiMH?:

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Standard NiMH self-discharge rather quickly.

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Look at: bq2002/C/E/F bq2004/E/H bq2005 bq24400/1

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Coulumb counter and measure four cells voltages (multichemistry):

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Glenn

Reply to
Glenn

Also look at:

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Glenn

Reply to
Glenn

I wouldn't advise this, unless you can reprogram the li ion charger and get a little more voltage from it. Charging NiMH cells in series in general isn't a great idea. If you do it, you have to be very sensitive to slight changes in the pack voltage, if you want to fast charge. You could alternatively use a dumb, slow trickle charger, but even then you have to be careful.

Reply to
Paul Rubin

series NiMH batteries, assuming appropriate current limits where in place. I understand that they may not achieve full charge, but could be charged to 80% I think. This is because I use NiMH batteries in my product and have to design the charging circuit and there is a lot more choice in Li-ION charging ICs.

Hi Steve

Please read about this, while designing:

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Fast, High Efficiency, Standalone NiMH/NiCd Battery Charging:

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Quote: "... The LTC4010 (16ben) and LTC4011 (20ben) are NiCd/NiMH battery chargers that simplify Nickel-based battery charger design and include power control and charge termination for fast charging up to 16 series-connected cells using a synchronous buck topology. ..."
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LTC1759 - Smart Battery Charger:

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LTC1760 - Dual Smart Battery System Manager:
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"... The LTC1760 implements all elements of a version 1.1 ?Smart Battery System Manager? except for the generation of composite battery information. ..."

LT3652 - Power Tracking 2A Battery Charger for Solar Power

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"...Resistor Programmable Float Voltage Up to 14.4V Accommodates Li-Ion/Polymer, LiFePO4, SLA Chemistries..."

Complete NiMH/NiCd Charger for 1 to 16 Cells:

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New:
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Glenn

Reply to
Glenn

Thanks, what a great lot of information. The reason I thought NiMH would be a good battery technology is that is is relatively safe if slow charged, easy to ship via air and customer installe d if need be and AA NiMH batteries can be purchased anywhere if required. T he unit requires a 5V rail of around 1.5amps, either from a Micro USB or vi a the batteries with smooth switch over, also the batteries will need char ging. We are a host device with 3 USBs and a Micro USB wall power supply in put. I did think of some variation of USB OTG such as the bq24195, however the Boost mode start up time is too long (200mS)and because it uses current termination for charging cannot fully charge NiMH battereis. If there is s ome Li-Ion battery pack with in built safety circuitry of a similar size an d cost to 3 AA batteries please point me in the right direction. Thanks again for all your advice and pointers

Reply to
steve

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similar size and cost to 3 AA batteries please point me in the right direction.

Hi Steve

This might be interesting. But the AA LiFePO4 has only

3.2V*400mAh=1280mWh, they are cheap, the LiFePO4 chemistry is very robust, might have very long life - it depends on how gas-tight the accumulator is made. I do not know their self-discharge rate. If water disappears the internal impedance go up.

(LSD-NiMH has 1.2V*2000mAh=2400mWh. May last 1-3 years)

US$8 (4 pieces)

4pk Solar Tech 3.2V AA LiFePO4 Rechargeable Batteries:
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3.2V; 400mAh AA Size battery LiFePO4

(Search for lifepo4 aa at amazon. The same product can have different prices)

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A123Systems M1-cell 2.3Ah 3.2V is as far as I can remember, laser welded (therefor very gas/water-tight) so it is estimated to last more than

10-15 years - even at high temperature (60°C) according to their brochure. More than 3000 full cycles:
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You can overcharge LiFePO4 chemistry, discharge to zero volt; then overcharge, overdischarge it (high ampere), reverse charge it, it won't explode according to many tests, but it will of course diminish the battery-life. (FYI: I have currently no shares in any battery firm ;-)

br,

Glenn

Reply to
Glenn

More about LiFePO4 batteries/accumulators:

SANDIA REPORT SAND2008-5583 Unlimited Release Printed September 2008 Selected Test Results from the LiFeBatt Iron Phosphate Li-ion Battery Thomas D. Hund and David Ingersoll Prepared by Sandia National Laboratories Albuquerque, New Mexico 87185 and Livermore, California

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Quote: "... Test results have indicated that the LiFeBatt battery technology can function up to a 10C discharge rate with minimal energy loss compared to the 1 h discharged rate (1C). ... The majority of the capacity loss occurred during the initial [!] 2,000 cycles, so it is projected that the LiFeBatt should PSOC cycle well beyond 8,394 cycles with less than 20% capacity loss. ... [See graph pdf-page 23] [ Read: 48% capacity available at -30°C. ] [ very useable! ] [ Read: 65% capacity available at -20°C. ] [ Read: 74% capacity available at 0°C. ] ...

3.8 Over Voltage/Charge Abuse Test In Figure 16 the events in an over charge/voltage abuse test are documented. Initially, as expected, the cell voltage increases quickly while being charged at 10 A, but then slowly increases after 4.7 V. The cell voltage slowly increases for about 30 minutes while the cell temperature continues to slowly rise to about 100 °C at which time cell voltage spikes to the maximum value of 12 V. At about 110 °C the cell vents liquid electrolyte without any fire or sparks and then open-circuits at 116 °C. After open-circuiting and a loss of electrolyte, the cell looses all voltage at 120 °C. The data acquisition shuts down due to a no voltage condition, but temperature is manually monitored until the cell reaches its maximum value at 160 °C about 20 minutes after the cell open-circuited. ..."

Nail penetration testing A123 Li-ion [ one of the best LiFePO4-batteries ]:

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Compare with the other Li-ion (non-LiFePO4):

Exploding Laptops on Good Morning America:

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Nail penetration testing Standard Li-ion:

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Spark, Smoke & Boom!: World's Most Dangerous Battery!:

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Modify Li-Po Battery Nail Penetration Test:

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Glenn

Reply to
Glenn

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