A simple charger for Ni-Cd and Ni-MH batteries. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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Yes, comrades. Now we will charge the batteries, simply, efficiently, and most importantly - quickly. Why use the MAX713 chip from MAXIM. This is a specialized microcircuit, sharpened specifically for charging these types of batteries.

So, what can she do - come closer, now you will see.

So MAX713 allows you to:

• charge nickel-cadmium and nickel-metal hydride batteries in quantities from 1 to 16 pieces at the same time;
• in the fast charge mode, adjust the charge current from C / 3 to 4C, where C is the battery capacity;
• in the slow charge mode, bring the batteries to condition with current C / 16;
• monitoring the battery status and automatic transition from fast to slow charge;
• in the absence of charging current, only 5 μA from the batteries “leaks” through the microcircuit;
• the ability to turn off the charge by temperature sensors or by a timer;

Well, that's enough - and that's how much it turned out.

As usual, in order to talk in detail, we look at the diagram:

(click to enlarge)

Generally speaking, as we remember from the old clay times, it was recommended to charge batteries with current 0,1Swhere C is the capacity of the battery. However, since then a lot of beer has flowed away and manufacturers have learned to make more advanced batteries that allow them to do such disgrace as a fast charge (Fast Charge).

"It's okey", they say - you can charge our batteries with much more current - the main thing is not to exceed the value of 4C, otherwise a big-bada-bum can happen.

Of course, the more charging current is used in the charging process, the less time is needed for this very charging. However, nevertheless, you should not get carried away too much - current is current, and the durability of the battery is also not the last thing. Therefore, the MAX713 implements not only fast, but also slow charging (Trickle charge), which turns on when the battery reaches full charge with a large charging current.

The circuit shown above allows you to charge two batteries, each with a capacity of 1000 mAh, with a current of C / 2, that is 500mA.

There is an indication of power on - HL1 and fast charge indication - HL2.

Batteries are connected in series.

The input voltage should be 6 volts. Are you still here? Well, run for a soldering iron!

What? Do you need to charge four batteries at once? And not 1000mAh, but 1200?

Well, then we don’t run after the soldering iron, but listen further.

As I said, this microcircuit allows you to charge up to 16 batteries, with a current of up to 4C. So, what is required of us in order to design a charger for our specific purposes?

1. Decide on the charging current of the batteries. It would be nice to know what the maximum charging current the manufacturer recommends. Well, if you don’t know, then it’s at your own peril and risk. For starters, I wouldn't go over C/2.
2. Decide how many batteries to charge at the same time. After that, according to Table 1, determine where to solder the leads PGM0 и PGM1. Of course, in order not to re-solder the microcircuit every time, you need to provide a switch if you need to charge a different number of batteries.
3. Select the input voltage for the charger. It can be calculated using the formula: U=2+(1,9*N),
   where N is the number of batteries
   But this voltage cannot be less than 6 volts.
   That is, if you charge even one battery, the input voltage should be 6 volts.
4. Determine the power of the output transistor, and then select the appropriate one from the reference book. Power is defined like this:
   P=(Uin - Ubatt)*Icharge,
   where:
   Uin - maximum input voltage,
   Ubatt - the voltage of the rechargeable batteries - the total, of course,
   Icharge - charging current.
5. Calculate the resistance R1. R1=(Vin-5)/5 - resistance is obtained in kiloohms, to get ohms, the calculated value must be multiplied by 1000.
6. Determine the resistance R5. R5=0.25/Icharge If Icharge is substituted in amperes, we will get the resistance in ohms, if in milliamps, then in kiloohms. Don't get lost.
7. Choose a charge time. This is necessary so that in the event of a faulty battery, the charger does not drive it, the poor fellow for an infinite number of hours, but turns it off on a timer, even if the battery is not charged. To select the charge time, use Table 2. And we twist our legs PGM2 и PGM3 according to this table. Of course, do not forget to take into account the charging current that has been selected, otherwise it may happen that the device turns off before the battery is charged.

As a matter of fact, that's all. Tables will follow.

Table 1. Setting the number of rechargeable batteries

Table 2. Setting the maximum charge time

Publication: radiokot.ru

See other articles Section Chargers, batteries, galvanic cells.

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