good UPS battery charger?

[ZippyDan]

I want to charge various UPS batteries, all 12V and 4.5AH, 7.5AH, 9AH, 12AH, 15AH and up

I have a big heavy duty car battery charger, but it is not very "smart" and I think it puts out too many amps for a UPS battery. It is rated at 12V 5A. heard you are only supposed to charge them at around 1.5A, which for many qualifies as "trickle charging".

Can anyone recommend a good battery charger for this purpose?

This one has good reviews and claims to charge at 1.25A, but it is also made for car batteries and it looks like it has differnt phases of charging, so I don't know if that 1.25A is just an average.

http://www.amazon.com/Battery-Tender.../dp/B00068XCQU

For example, when I tried hooking up a battery to my car battery charger which is supposedly 5A output, it showed 10A on the meter.

 

[imagoon]

Better chargers have current limiters you can set. A smaller trickle charger like you linked would charge bigger batteries it would just take a lot longer (assuming the trickle charger is self limiting otherwise it might fry itself but must are self limited) but it would be smart enough to start limiting the load as the voltage rises to charged.

I picked one up at Autozone for the motorcycle and it worked fine all winter.

 

[aigomorla]

100W solar panel with charge controller..
thats how i recharge my AGM batteries and its off the grid + green!




However if u want a faster solution, look for almost any 12V charger.
yes the one u linked should work fine.

 

[ZippyDan]

100W solar panel with charge controller..
thats how i recharge my AGM batteries and its off the grid + green!




However if u want a faster solution, look for almost any 12V charger.
yes the one u linked should work fine.

but saying "any 12V charger" is innacurate also, isn't it? I have this charger

http://akum.lt/wp-content/uploads/2011/08/DFC10.jpg

but I am told it would be unsuitable for charging smaller UPS batteries

 

[imagoon]

but saying "any 12V charger" is innacurate also, isn't it? I have this charger

http://akum.lt/wp-content/uploads/2011/08/DFC10.jpg

but I am told it would be unsuitable for charging smaller UPS batteries

Batteries will draw what they can while they are charging. Most have a max amp rating that the charger will limit to to prevent heat damage / boiling / explosions. A 10 amp charger should not charge a battery that has a charge rate of less than 10 amps. You are quite correct unless that unit has a dial to change the current limit (some do.)

 

[Nec_V20]

I would recommend the CTEK MXS 5.0. It's pricey but it will also recondition batteries.

 

[ZippyDan]

Batteries will draw what they can while they are charging. Most have a max amp rating that the charger will limit to to prevent heat damage / boiling / explosions. A 10 amp charger should not charge a battery that has a charge rate of less than 10 amps. You are quite correct unless that unit has a dial to change the current limit (some do.)

So the battery can draw 10 amps, but that doesn't mean it SHOULD. Am I correct that UPS batteries should not be given more than 1.5 amps? It is possible to give more in bursts but it would cause too much stress over a long charge cycle. Basically, the battery is too dumb to limit its draw, and the charger is too dumb to limit its output.

 

[bryanl]

An UPS typically applies a charging voltage of no more than 13.8V and a current limited to 5% to 10% of the battery amp rating, or 250-500mA in the case of a 5 A-H battery. A manual car battery charger can be used if a resistor is inserted in series, something in the range of 50 ohms and at least 10 watts.

 

[Red Squirrel]

Find out the recommended float voltage of the cells and get a charger that can charge at that, or let you select. Typical is 1.25 per cell I believe (12v has 6 cell, so 13.5v). The battery will only draw the amps it "needs" and you can leave a battery on float indefinitely. Some smart chargers will tweak the voltage during different stages to speed up the charging process though, so if you are bulk charging many before they are put into service this may be what you want. You'll just want to limit the current to like 2 amps or something. Most car battery chargers will work ok for this, you can select between gel and flooded mode. I think gels take a slightly higher float voltage.

 

[imagoon]

The battery will only draw the amps it "needs" and you can leave a battery on float indefinitely.

This is not generally true. At battery can and will draw current based on the internal resistance of the cell which goes down as the cell gets drained. It is entirely possible for a cell to have a max charge rate of 10 amps and in an uncontrolled charge, pull 30+ amps. This will over heat the cells during charging and will cause them to boil off or vent.

 

[imagoon]

So the battery can draw 10 amps, but that doesn't mean it SHOULD. Am I correct that UPS batteries should not be given more than 1.5 amps? It is possible to give more in bursts but it would cause too much stress over a long charge cycle. Basically, the battery is too dumb to limit its draw, and the charger is too dumb to limit its output.

Correct but you should look at the battery spec sheet to find the max charging current for the battery and use anything below that.

You rarely see this issue with car batteries because they can take some pretty significant charge rates and most chargers sold for automotive have a current limiter in them already.

 

[Red Squirrel]

This is not generally true. At battery can and will draw current based on the internal resistance of the cell which goes down as the cell gets drained. It is entirely possible for a cell to have a max charge rate of 10 amps and in an uncontrolled charge, pull 30+ amps. This will over heat the cells during charging and will cause them to boil off or vent.

Yeah true, if there is an issue with the battery it could also go in thermal run away. Good idea to monitor batteries being charged especially if they are unfamiliar batteries (ex: you found them and want to see if they are still good etc).

It's also a good idea to fuse permanent strings of batteries in case such event occurs.

 

[aigomorla]

Blah... RS is correct...

I wasnt assuming you would overshoot charge Amperage...
And yes litiums are notorious for undergoing Thermal run aways...