what size supercap do i use to charge a 10000ma battery

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What voltage to apply to charge a vii.ii 5 Battery?

• Thread starter Lac
• Start date Apr 21, 2004

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• #1

I'one thousand most making a batterycharger, charging a Ni-Cd Battery rated at 7.2V 1500mAh, but what should the charge voltage be? 7.ii 5? at the orginal charger I measured around xi.8V when the charger was ON but the battery asunder.

Anyone know the right voltage?

Thank you!
Lac.

• #2

A very simple answer is plenty voltage to yeild the desired corporeality of current to flow into the battery. The voltage practical will always take to be slighly above the bombardment voltage at any given moment in guild for the battery to charge. The open up circuit voltage of a simple charger may be very high relative to the desired battery voltage but considering of it'due south design only a limited current will menstruum. The resulting voltage settles where it settles based on internal resistance and other things.

There are limits to the rate at which you lot can accuse a battery. Use of a charger based on voltage solitary might ruin the bombardment or worse, create a dangerous situation. Some batteries are fabricated to exist charged at high rates, others aren't. Sorry to be so unclear but information technology's not a elementary question.

If you aren't concerned near the time charging takes yous might construct a uncomplicated current limited charger with a ten or 12 vdc ability supply capable of delivering 50 to 100 milliamps. Run across the datasheet for an LM317 - information technology shows a simple current regulator that y'all could set up for 50 or 75 ma. It might take 24 hrs to charge the battery simply yous stay way away from overheating and other problems. There are numerous ways to charge batteries at faster rates - some very circuitous but that preserve battery life - some simpler at the expense of time or some bombardment life. Many of these are described at websites- you lot might search prior posts nether battery chargers. Some of these are really sophisticated but thanks to modest price ICs are inside the range of a person with pocket-sized electronics skills.

As a general rule, from what I've seen - a simple, low-price charger can be used if time is non an upshot. As the desire to reduce the time becomes a bigger gene then more elaborate schemes are applied to increase the accuse rates in a way that minimizes danger -mayhap at some expense in battery life. My son used these batteries in and then called fast chargers. They did piece of work and the batteries got hot but didn't explode. I think that it was more than "cut and try" rather than good design on the office of the charger manufacturer. I'm besides convinced that bombardment life was much less than it could accept been but and then like everything else in life you trade on thing for another.

You lot could "cutting and try" using the scheme I described, increasing the current. That IC (LM317)is adept for an amp or more than. I tin can't tell you how hot is too hot for the battery or at what indicate it might let go. An amp gets the accuse time downwards to a few hours or less. I've no manner to determine if you apply 12 volts if the battery volition charge at 1 amp though I'd think it would.

• #3

Hi Lac

Use the peak observe technique to decide the voltage needed.

Ante :roll:

• #4

Geez! your good stevez! This bombardment is a part of a backup circuit where the battery charges, as long as the excursion gets ability from a walloutlet, but in one case the power from the walloutlet is cutting, the battery kicks in.

Then the charging time doesn't need to be fast, I call back 15mA is enough, 1%. And so 9V (or more?) would exist enough to charge the bat?

Thanks!
Lac.

• #v

If you plan to leave this on line constantly there might be some issues with a constant trickle charge - though with very depression electric current the likelihood of a trouble ought to be low.

It would exist dainty to put something in to plow the charger off, plow information technology on. The trouble is that the departure between a fully charged battery and partially discharged 1 isn't great - and all of that changes with temperature and from battery to battery making it very difficult to know with any certainty what level of accuse is contained in a bombardment. By the time a actually profound difference exists you'll accept a nearly expressionless battery.

Really good chargers account for temperature and watch the incremental changes in voltage over time to indicate where things are at. Good project for a PIC probably but besides many things on my to-do list already.

• #6

Correct voltage for charging

Nicad batterys have very close to 1.5V per jail cell across their terminals at room temperature. If you construct a constant current charger of the Capacity of the cells times 0.095 the charger tin can be left on all the time with out damage to the cells, this is at normal room temperature almost 74 degrees F.

In your case 1500Ma Ten .0.095 = 142.5Ma. But as others have suggested
about 100Ma would be fine. As long as the charger will supply 9V at your charging current everything should be great.

• #7

thank you! Just one more than question: Can I use 12V instead of 9V to charge the bat?

Thanks!
Lac.

• #8

Lac
Yous don't charge nicads with Volts you charge with Amps the voltage is irrelevant.

Ante :roll:

• #9

Nicad Charger

I agree you charge nicads with current, just the charger must exist capable of supplying nigh 1.5 volts per cell at the battery terminals to fully accuse the battery.

• #x

Absolutely, but if the current is right why measure the voltage? At that place should of curse exist some slack regarding the voltage, I would recommend 2Volts / cell to be on the prophylactic side. The higher the charge current the college the voltage get over the cells.

Ante :curl:

• #11

I have used anywhere between 12-14 volts.

Back when I started in Radio control, I used a crude method to accuse batteries, which included a timer switch and feeling it to see if the battery got to hot.

Trickle charging gets the cells in a bombardment to equal levels, non all cells will be necessarily full. That is why alot of professional Radio command racers used Matched cells.

• #12

NICAD's should be charged with a constant current, an extremely simple fashion to do this is a loftier value resistor from a high voltage. Assuming a loftier plenty voltage isn't available, y'all can use an electronic abiding current source to practice the same affair - I would suggest 12V or so for charging vii.2V from a constant current source.

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