UPS battery replacement: lead-acid to Ni-MH chances

[Barkuti]

Hi,

OK. I just dropped by looking for advice in a somewhat technical question I found no better place to ask. There we go

Family business, managing a lottery and gambling office of a state company. Games/bets are served over a propietary computer/data network over ADSL, serviced using a propietary software system online terminal. Terminals must be kept online at all times...

And for convenience, we safeguard the terminal from power failures using a SAI (power outages while servicing transactions means stupid reporting downtimes; other critical operations benefit aswell). So it may be convenient and useful for us to run the terminal SAI powered when a blackout hits. Moreover, the SAI has no possibility of management.
You get the picture. Lots of deep cycles for the poor cheap lead-acid SAI... dead battery.
BTW, SAI is a Riello iDialog plus ID60 -600 VA-.

Using a standard automotive battery apparently fixes the deep cyclation/battery overload issue, due to much higher capacity. But if power outs when no-one is in the office... battery will still die, even if it takes 4 or 5 hours. With a blistering stated recharge time of 6-8 h for the puny 7 Ah standard battery, expect at least a couple days to get the big one back into full condition! lol

So I was wondering about the possibility of fitting a custom built Ni-MH to the SAI (no deep cycling issues thus).
Lets say, for example, a 10S6P (10 in series, 6 in parallel, 60 cell array) of 2600 MAh AAs.
Voltage range is 12 to 15 V. Nominal voltage is the same as in the lead batt, and peak voltage is high enough so no over-charging problems should arise (lead is usually charged to 2,4 or 2,45 V per cell, 14,4 - 14,7 V peak).
MFG (over)stated peak capacity 15,6 Ah. Let's say the battery is good for 12 Ah.
The UPS would, at most drain barely above 30 Amps at peak load. That means a 2,5C worst case scenario discharge rate. 1C discharge rate for typical operation. Should be handled easily by the cells.

OK. That's my idea. Now, if someone has something so say about UPS batt charging circuitry messing around here or there, or whatever... do it!
Thank you in advance.

Regards,
Barkuti

 

[FredWagner]

I'm unfamiliar with the SAI acronym. If it's the same an UPS as in the forum title, we're good. The charging circuitry in your Riello Dialog Plus is designed for Lead-Acid. It would have to be modified to properly handle NiMH or any other technology. How many of these terminals are you supporting ? dozens, hundreds, thousands ? How many times a year or month do you experience a power failure that outlasts the batteries in your current units. There are UPS's available (APC comes to mind) that are designed so you can add battery capacity as needed, but they're not cheap. Or you could just get an 'ordinary' UPS with a much higher VA rating, and it would have longer battery life in stock configuration with the load from your terminal.

Fred Wagner

 

[etarhan]

a) Battery charging algorithms for lead acid and NiMH are quite different, which means that these NiMH cells OR the charging circuit of your UPS may blow out in short time (even literally!).

b) Capacity ratings for NiMH (or other technology) batteries do not indicate the current you can draw from the battery in a sustained session. mAH rating only indicates the total power you can expect to draw from the battery. From experience, I know that drawing 2600 mA from a 2600mAH battery kills it so fast that you would think the battery was faulty from the start.

c) I would use a separate charger to charge the lead-acid batteries FAST whenever needed, and hook it up through a relay so that when mains power is available, the batteries are disconnected from the input of the UPS (to isolate the higher charge voltage). If the trip speed of the relay in case of a mains failure is unacceptably slow (a slim chance, but...), I would hook the relay so that one battery would be in constant touch with the ups, and the rest of them would be charged by the external charger.

Good luck.
Engin Tarhan

 

[technome]

Barkuti...
Unit you have is 600va, likely that is input, output is likely much less, around 400 watts.

LiMh
(10 in series, 6 in parallel, 60 cell array) would give you...
60 cells x 2600ma (2.6 amps)x 1.2 volts= 187 watts, enough to run an average PC desktop for about an hour.

As Fred stated, LiMh batteries require a total different charging circuit, with a more robust voltage or temperature circuit.

http://en.wikipedia.org/wiki/Nickel-metal_hydride_battery

What you need is as the link below. I have a couple dozen of these units at different clients, they a refurbished ( new batteries). I never buy "new", as most unit I purchased "new", sat on a shelf for a year before shipment (half dead batteries). If your server is dual power supply, each power supply can be plugged into one of these. These units weigh 140 lbs, most of which is battery weight. Not sure of your location, but there are many dealers selling refurbished UPS units.

http://www.refurbups.com/APC-SU3000RMXL3U-Smart-UPS-3000-Rack-Mount-XL-3U-Black

........................................
Chernobyl disaster..a must see pictorial

http://www.kiddofspeed.com/default.htm

 

[john09871234]

Hello
Before replacing lead acid battery with nickel cadmium battery proper precautions should be followed and avoid direct contact with the acids in the battery
.......................

JohnMiller

http://www.topsyssolutions.com