I’m sorry for being so off topic, but I figured this would be the most appropriate place to ask my question.
Recently, my area (San José, California) has been getting more than its fair share of power outages, and I’ve been wondering about investing in a UPS for my computer, and a few other things. I recently had the chance to open up an older (but not ancient) UPS, and was slightly disappointed when I found a 12V 2.2Ah battery.
Now, FIRST has given us 18Ah Exide motorcycle batteries in the past, so I’ve been thinking about replacing said 2.2Ah battery with a cell which has more capacity. After the thought of pilfering a battery from my team crossed my mind, I began wondering about the plausability of using a typical car battery as the cell of a UPS.
When researching car batteries (mainly on a trip to the local Costco’s automotive and handtool section) I saw many references to a “Cold Crank Amperage,” being the amperage said battery could output at 32degF with no amount of time appended (so as to calculate Ah), but I could never find a description of any of their batteries in Ah, so I couldn’t really tell what I was looking at.
If anyone could enlighten me on any of the technical aspects of lead-acid cells, or even general battery theory, it would be much appreciated, along with the specific feasability of replacing the standard cell of a UPS with that of a higher capacity.
Thanks in advance.
The batteries FIRST gives us are gel cell batteries, the electrolyte is in the form of a non-spillable gel, not liquid hydrochloric acid like in car batteries. The acid in a battery is not so strong that it will dissolve things before your eyes like acid in the movies, but if you spill it on your hands and don’t wash immediately and throughly it will start to burn and itch about as bad as a bad sunburn. And if you get it on your clothes, the next time you wash them there will be perfect holes the size of the drops of acid that got on them. So what you save in battery cost you will wind up paying in clothes or carpet cost. Car batteries also give off hydrogen gas when being charged, so it is not safe to charge them in a tightly sealed area where the gas could concentrate to explosive levels, I think this warning applies to gel cell batteries also.
About CCA (cold cranking amps) and Ah (amphours). Amp hours are a measure of a battery’s capacity at a certain discharge rate, usually at 1/10 of the battery’s capacity. For example, the battery you mentioned was labeled 2.2 Amphours. You would think this means the battery can deliver 2.2 Amps for 1 hour, it probably can’t. But it probably can deliver 0.22 Amps for 10 hours. The slower you drain a battery the more you get out of it up to a point. A car battery is designed to deliver hundreds of amps for just a couple seconds. So, CCA is the current a battery can deliver for a very short time and it doesn’t’t tell you anything about the total capacity of a battery. Car batteries are also designed to be always charged up and if you discharge one completely it damages the battery. After all that, you can buy a better battery. Look in the yellow pages under batteries and tell them you want a gel cell, deep cycle battery, in my area they are sometimes called trolling motor batteries because people use them with small electric boat motors for fishing. Surplus catalogs like www.allelectronics.com and www.goldmine-elec.com sometimes have good deals on surplus batteries.
As to your original question on the UPS. A 2.2AH battery is a pretty small UPS. However the electronics in the UPS are designed around using that battery. Some of the things the UPS is ckecking and/or adjusting are battery health, charging current, load current, etc. By using a higher amp hour battery may affect any of these conditions besides the problem with enclosing a larger battery in the same UPS case. This is not maintenance I recommend a newbie perform for the obvious reason that a UPS generates lethal, repeat LETHAL voltages as part of it’s normal operation.
As to the second part re:cold cranking amps. This is a marketing (mostly) term that relates to how many amps can be delivered by a new, fully charged battery at a specified temperature. It is more of an indication of the internal resistance of the battery at max rated current at rated temperature.
Many manufacturers include the Amp Hour rating in the model number of the battery, i.e. a MV1260G battery would generally be a 12 volt 60 amp hour battery in a manufacturers “G” case style with “MV” terminals. Batteries for new cars are chosen by size available for mounting and how much current is needed for accessories. A van with a big lighting package, power everything and front and back air conditioners will need a higher capacity battery than a sub compact with manual windows and no air.
Found these definitions on a site this morning. They are not official but you get the general idea…
CCA Cold cranking amps. Maximum number of amps a battery can supply for 30 seconds at a temperature of 0 degrees F, before dropping to 7.2 volts. This is a more severe test than MCA and results in a lower number.
MCA Marine cranking amps. This is similar but is measured at 32 degrees and so results in a higher number for the same battery.
Amp Hours This is normally measured at a 20 hour rate. The amp hour rating is the number of amps a battery will supply for 20 hours at 80 degrees F before dropping to 10.5 volts, multiplied by 20 hours. ie If a battery can supply 5 amps for 20 hours then it is called a 100 Amp Hour battery.
Reserve Capacity The number of minutes a battery will supply a specified constant current (normally 25 Amps) at 80 degrees F before dropping to 10.5 volts.
This measure is more appropriate for an automotive application and is intended to tell you how long you can keep driving with a dead alternator.
Thank you both for the information.
I guess at this point we all have more on our minds (and in our schedules) than personal projects, but it’s very useful information to have.
Thanks again, and good luck this season.