How to check a battery charger?

[gunner55]

Over the years we have collected 3-4 maybe 5 chargers that have been used on our boats.At least 2 maybe 3 of them don't work right anymore.Does anyone know how to set them up to check them with a meter?I would like to get rid of the bad ones as this Spring I found 1 of our batteries had been boiled over.

[Tom7227]

Are you talking about on-board chargers or the ones you hook up in the garage?

 

[gunner55]

Sorry I wasn't very clear,the garage type is what I was wondering about.

[Tom7227]

If the battery boiled over it could well be that you were charging it too fast.  Search battery maintenance and read a few of the links and you will learn a lot about what makes things work better.

 

[BobT]

Most chargers are incapable of actually charging a battery too fast.  Current is usually limited to about 20A or less and output voltage should be less than 14vdc.  Unless a battery charger is designed with smart technology where it is capable of detecting when the battery is fully charged, you need to use due diligence to prevent the charger from over-charging.  A plain battery charger will typically output somewhere around 14vdc give or take.  If you leave a charger connected past the point where the battery is fully charged, the applied ~14vdc can heat up the battery and the water can evaporate.  

Note: with smart chargers the output voltage will vary throughout the different charging cycles.  For example, my charger starts out at just over 12vdc output but allows up to 20A current until the battery reaches about 90% charge. Then it limits the current and increases the voltage output to about 13.8vdc to finish the battery. Once completely charged it goes into a maintenance mode. 

Even with on-board smart chargers, one must check electrolyte levels regularly.  

 

[gunner55]

Thanks guys.Most of our chargers have a 2 amp,15 amp & a 75 or 100 amp settings except the smart charger we use down at the lake.Is it possible that the water level was too high & that made it overflow? All I do know is when it went in the boat this spring the bottom of the case that it was setting in was wet & my hands stung a bit from handling it.The baking soda water we poured in the case reacted quickly.I also keep a small bottle of distilled water in the boat toolbox & check the levels every month or so depending on use.Or maybe the settings switch isn't working right & actually putting out 75/100 amps when it's not suppose to. Is that possible?

[BobT]

The best setting to use is the 15A setting.  The general consensus from my research is that you want to recharge your batteries as soon and as quickly (within reason) as you can after each use.  The 15A setting will be sufficient for this.  Once your battery has fully recharged, disconnect it from the charger as soon as practical.  You don't have to be super concerned about leaving it connected overnight or for a little longer than necessary but I would not recommend leaving it connected for extended periods unnecessarily.  

The 100A setting, if working correctly, should pulse the output on and off automatically and is used for starting an automobile or similar by providing a high-current supply to the starting motor that is demanding it.  I don't like to use this feature myself.  

 

The 2A setting can cause trouble as I have learned from personal experience.  Your battery's internal resistance is critical to proper monitoring by the charger.  If the internal resistance has deteriorated to something less than new, the charger can get fooled into thinking the battery is not done charging when it really is as full as it will get and so the charger will continue to apply voltage and possibly overcharge the battery.  This is because the battery even once fully charged may draw enough current to fool the charger.

 

[gunner55]

I agree as we don't usually use the 100A either.What we usually do is at the end of the season when we pull them from our boat is to check the water level & fully charge them with the 15A setting.Then when they are charged we put them on a 1/2A float charger until they are put back in the boat.