What is the difference between nicd and nimh battery chargers

Asked 3 years, 7 months ago. Active 1 year, 11 months ago. Viewed 17k times. Now I just went and bought a new pack with a charger anyways, and it's NiMH. Lorenzo Donati -- Codidact. Add a comment. Active Oldest Votes. Fast charge, on the other hand, may give you issues, because it needs an end-of-charge detection circuit that works differently between the two chemistries: Fast Charge Fast charge for Ni-Cd and Ni-MH is usually defined as a 1 hour recharge time, which corresponds to a charge rate of about 1.

Olin Lathrop Olin Lathrop k 36 36 gold badges silver badges bronze badges. Nicads aren't anywhere near as touchy as lithium batteries. Nicad in a NiMh charger should be fine. Trickle charge is fine as long as you keep an eye on the charge time, and fast chargers for NiMh will also detect a full Nicad and shut off the charge cycle. Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. On the other hand, if the charge current is too high, the battery may become excessively hot requiring an NTC thermistor located near the battery to pause the charge cycle allowing the battery to cool down before resuming the charge cycle. When the battery temperature is within limits, the battery voltage is measured and must be below the max limit.

Several hundred milliseconds after the charge cycle begins, if the battery voltage exceeds 1. This overvoltage condition usually means the battery is defective requiring that the charger be manually reset by replacing the battery, toggling the shutdown pin, or removing and reapplying power.

This hold-off-time ranges from 4 minutes to 15 minutes depending on the charge current and charge time settings. During the charge cycle, the battery voltage slowly rises. When the battery approaches full charge, the battery voltage begins to rise faster, reaches a peak, then begins to drop.

The charger continuously samples the battery voltage every 15 to 40 seconds, depending on charge current and timer settings. A user programmable recharge feature starts a new charge cycle if the battery voltage drops below a set voltage level because of self-discharge or a load on the battery.

Also, if a fully charged battery greater than 1. If the timer stops the charge cycle, it is considered a fault condition and the charger must be reset by removing and replacing the battery, toggling the SHDN pin or toggling the input power to the charger. For example, a mAHr rated battery can supply a mA load for one hour before the cell voltage drops to 0.

Because of chemical differences between the two battery chemistries, NiMH cells generate more heat when fast charging.

For applications that require a load, refer to the power path components shown in Figure 2. When the input voltage is present, the load is powered from the input supply through Schottky diode D1 and the battery is isolated from the load.

Many of the inexpensive NiMH battery chargers are simply NiCd chargers that have been modified slightly. Typically a 5 hour NiCd charger has a switch that allows the charge time to be increased from five hours to eight hours.

Thus a 5 hour NiCd charger becomes an 8 hour NiMh charger. As we mentioned above, we do not recommend this type of charger design. While a timer type charger is less expensive to manufacture than a smart charger, it can lead to overcharging and battery damage if batteries are frequently charged before they have been discharged that is, the batteries are used for a short time and then fully charged again. NiMH smart chargers have actually been designed to detect when a NiMH battery is fully charged and then shut off or go into a trickle charge mode.

Because of the more complex circuitry, this type of charger costs more to make, but should lead to greater battery life. Some of these chargers only cost slightly more that the "dumb" chargers.

The answer to this question depends on the type of NiCd charger. Depending on the type of NiCd charger you have, the older NiCd charger may undercharge NiMH batteries most likely , it may overcharge them less likely , or it may charge NiMH batteries properly but it's not likely to do so automatically and could take a very long time.

Let's take a look at the three cases. Many of the older NiCd chargers are the simple timed type charger which will charge batteries for a fixed amount of time and then shut off. Unfortunately, since NiCd batteries have a much lower capacity than NiMH batteries, the timer is likely to shut off long before the NiMH batteries are fully charged. This won't harm the batteries, but the NiMH batteries won't be fully charged since the timer will have stopped the charge cycle too soon.

Also common among older NiCd chargers are the so called "overnight" chargers which charge batteries at a low rate as long as the charger is plugged in. This type of charger can fully charge NiMH batteries, but it might take a very long time to do so.

It's possible that an old NiCd charger could take as long as 48 hours to fully charge new high capacity NiMH batteries! This type of charger is not likely to damage NiMH batteries unless the batteries are left in the charger for weeks at a time, but it may not be very convenient to use. If you have this type of charger you can get an idea of how long you'll need to charge your batteries by using the calculator found above. The final possibility is that the older NiCd charger is a rapid charger that will charge NiMH batteries but will not have the necessary circuitry to stop the charge cycle once the NiMH batteries are fully charged.

If the NiCd charger is designed to charge batteries in less than two hours it may be this type. In this case the risk is that the older charger will overcharge NiMH batteries. This will be apparent if the batteries get very hot during the charge cycle. It is normal for NiMH batteries to get warm as they become fully charged, especially in a rapid charger. If the NiMH batteries get too hot to handle and stay that way for more than 20 or 30 minutes, then the NiCd charger is most likely overcharging the NiMH batteries and may shorten their life.

You would be most likely to encounter this type of charger if the charger was designed for rapid charging radio control RC vehicle batteries. This really depends on what you are going to use them for exactly.

NiCD batteries are commonly used for power tools and in that capacity they are in many ways superior to NiMH batteries. For high drain digital devices where weight is of primary importance, NiMH batteries are the best choice. NiMH batteries are also considered an environmentally friendly battery chemistry. NiCD's are toxic and recycling them is mandatory. NiMH batteries are a much more modern phenomenon.

Research and development began at the Battelle-Geneva Research Center in , and was satisfactorily completed in The chemical composition of a standard nickel-metal hydride battery looks like this: a nickel hydroxide positive electrode plate, a hydrogen ion negative electrode plate, a separator, and an alkaline electrolyte such as potassium hydroxide.