Motomaster Battery Charger How To Use

[Sanny Olafeso]

Whena battery is very cold, partially charged or sulfated, it will not draw the full rated amperes from the charger. It is both dangerous and damaging to a battery to force higher amperage into it than it can effectively use in recharging.

There are situations where a 'smart' battery charger won't recognize a battery because the battery is deeply discharged. Some chargers have a relatively high voltage threshhold. Remember, a 12 volt battery (adjust numbers for 6 volt, etc.) is effectively discharged at 11.9 to 12 volts (fully charged is 12.72 volts). A battery can be drawn lower than this, particularly if allowed to remain totally discharged for extended periods. This is not particularly good for battery health, and may in fact destroy the battery, but that is not for this discussion.

Some of the more common 'floating chargers' for vehicle or other battery maintenance, have threshhold voltages between 8 and 11 volts. If your battery voltage is below the particular level of your charger, the charger won't acknowledge a viable battery hookup, and won't pass current. Some chargers indicate a fault mode (continuous flashing), and others just don't do anything. Some charger manufacturers don't consider a battery below their threshhold voltage as worth recharging (they're not necessarily correct). Some, particularly marine battery chargers, are designed to check for battery voltage before passing voltage/current to prevent sparks, in case the charger is plugged in without being connected to a battery, when there may be a gas buildup in the compartment. All of our chargers have very low threshholds, and will charge deeply discharged batteries.

There are a couple of ways to get around this, to see if your battery will recover and take some charge. It still may have to be desulfated later. First, a non-intelligent charger, like you had in your garage 25 years ago, may be used with supervision, to cram some current into the battery, which will raise battery voltage. This is another case for having a decent digital voltmeter around the shop/house. You can keep checking the battery until it has enough voltage to register on the 'smart' charger, then let the smart charger take over. If you have golf cart type 6 volt batteries, you can series a pair (positive to negative) to look like a 12 volt battery, and use a 12 volt charger as above. Second method, if you don't have a 'dumb' charger: parallel a second battery (positive to positive, negative to negative) that you know to be recognized by the charger, with the bad battery, and attach the charger. After the charger has a while to put some current back, disconnect the good battery. It may take a time or two to get the charger to stay running. What you don't want to do is leave both batteries connected for a long time, as the good battery will end up overcharged. So, both methods require supervision.

Lead-acid batteries are charged in 3 stages, first by constant current (with voltage limit), then by constant voltage (with tapering current), then in the end during float charge the voltage is reduced to a float charge voltage level.

The 2 ampere and 10 ampere options allow charging different capacity batteries. You would use 10 amperes on a car battery and 2 ampere on whatever small batteries you might want to charge that still use the same voltage. For example, a motorcycle battery could use the 2 ampere charging option. Many lead-acid batteries only allow 25% of the capacity per hour: 2 amperes could then be used to charge at least 8 amp-hour batteries, whereas 10 amperes could be used to charge at least 40 amp-hour batteries.

An ideal battery charger does 3-stage charging based on the battery voltage - to quickly charge in the midrange, taper the charge near full, and then trickle at the right rate once full. This requires a fair amount of intelligence in the charger.

This is a cheaper battery charger that doesn't have that onboard intelligence. Instead, it lets you manually switch rates. If you will be monitoring the charge actively, you can punch up the 10A rate. If you will be walking away from it for hours or days, select 2A and that will better approximate the trickle charging it should get when full, so you will do less damage.

There are also "fast" chargers that will charge at 50 or 60A to boost a flat battery so it will start a car. Used once is usually ok if the battery is not already damaged, but if used on the same battery for long periods it damages the battery.

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