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Guest Staggerwing

Replacement batteries for UPS

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Time to replace my batteries.. (APC Back UPS 650)Has anyone here used a much larger sealed battery outside the UPS case rather than buying the 12ah batteries that fit inside ? (And cost as much as a MUCH higher amp sealed battery...)I'm really thinking about going with a small sealed auto battery behind the desk and forget about the expense and short run time of the regular batteries.Thanks,Staggerwing

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Staggerwing, There should not be any problem with connecting an external car battery outside your UPS box, although there might be a small difference in the car battery voltage in the trickle charge mode compared to the sealed 12Ah battery. This might confuse some charge logic thinking the battery is fully charged while actually not the case. But trying won't hurt. Just make sure you don't use long cables from the UPS to battery, as the current is considerable. 20 - 30Amps or so depending on the load. With your RC background you should have any problem setting this up. Remember that car batteries likewise sealed batteries need regular discharge charge cycles, or their lifetime is reduced considerably. That's why UPS batteries normally don't last long. At our local junkyard I see tons of UPS being discarded because of dead batteries. They make nice emergency mains power units with the frequent power outages we have here. (they also have nice MOSFET's inside for building RC speed controllers ;) ) RgdsRoland

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Stag,I haven't tried that but you definitely don't want to use an automotive battery. If you run it down a few times it'll be toast. Also car batteries can give off explosive gases when they're being charged. You want to use a deep-cycle battery intended for use in devices. Yuasa and some other companies make them. Here's a place on the web that has such things: http://protectiontech.com/battery.htmI usually find these kind of batteries at electronics surplus stores. If you have any in your area, check 'em out.

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Thanks guys...I don't think I'd ever run down a 500+ ah battery using it as a UPS supply. In all the time I've had a UPS I don't think it's been on battery more than 10 mins total :-)I'll be looking at sealed gel cell, deep cycle type battery for this use.Best,Staggerwing

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Staggerwing,At the risk of giving free tech support to a competitor's product??!?By all means, adding an external battery will increase your backup time (and your charge time by a corresponding amount). Many small UPS use 4.5 or 7ah batteries for 3-7 minutes backup. Adding another set will more than double your backup (and recharge) time. Always use sealed lead-acid type batteries. Automotive batteries are not designed for standby use and will 'sulphate' over time. They also require slightly different charge voltages.NOTE! Seriously! It is always advisable for any 'standby' UPS with only internal batteries that a battery be left in the UPS with the external one connected in parallel via a fuse. The reasons are voltage drop, stability and noise. Although you can use thick wires, you are adding inductance and this, together with the inverter switching characteristics will cause a higher voltage drop. As the batteries discharge, the inverter current increases until the 'low battery' detector shuts down the UPS. The internal battery maintains a low impedance close to the inverter. Some UPS will blow up if you don't do this (I know, I've done it...). Put a new battery in it and add another one externally - my old '400 gives me >60 minutes with a 33ah battery!Jon Point*************************(effyouthree@hotmail.com)*************************

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Thanks for the added info Jon !Great, now I have to spend even MORE money on batteries... I was trying to eliminate the overpriced 12ah that are in there now :-)Can't be done for less than $55.00 USD that's as much as a large external battery here.Guess it's just standard replacements for now...Staggerwing

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Jon,Thanks for the info on keeping the original battery and hooking in the extension. Didn't know that was critical.Staggerwing,Does that $55 price include shipping? ProtectionTech's 12v, 12ah batteries are $36 and $42.

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Peter,Yes, that's delivered.... ONLY way I ever figure anything :-) Otherwise you're kidding yourself.I found a couple of 12ah 6volts with a delivered price of $26.00 now.That means I will be able to swap the internals out AND add an external for a reasonable price. I don't know WHY they don't just build the UPS (apc Backup 650)around a 12v battery rather than two 6volts ?? Seems like it would make more sense..Thanks again,Staggerwing

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Oh, they're 6 volts. I didn't know that. Must be a cost issue. Perhaps the use of 6 volts batteries means they can buy X times more of the same batteries rather than some 6V and some 12V in order to get a better price (reduce their cost).

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Folks,The reason for the 2x6V is probably form factor. By far the most common battery used in UPS until 2 years ago was 12V/7ah (Yuasa NP7-12/Yuasa PS12700/CSB 12-7 etc). These can be had in Australia for $13-$17 from a wholesaler or ~$25 from elswhere (or up to $40 if you're not careful!)In recent years, due to industrial design issues, many UPS manufacturers have gone away from standard batteries. This is mostly because current designs are 'world designs' meaning one model is sold world-wide, usually with a domestic US variant. Due to the large production volumes involved and the manufacturer's desire for a unique product, the battery manufacturers redesign their batteries to fit in thinner/wider etc spaces. Powerware (no wars please) use many different types of batteries in their current range and, as a spare part are far more expensive than their previous generic counterparts. Suffice to say, if the total voltage is 12V, you can probably just use a single 5ah or 7ah 12V battery inside the UPS (just pack some foam around it) and use whatever is economical outside the unit e.g. 1x 7ah inside and three outside (all in parallel) will give you 28ah for a total cost of ~AUD$60/US$35. Use shrouded 4mm 'banana' connectors on the back of the UPS - they work well up to ~30A. This would extend your backup time by about 130% (~336w/hr). Hope this all makes sense!Jon Point*************************(effyouthree@hotmail.com)*************************

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Yep, makes sense. Thanks for all the info Jon. It's quite enlightening. In fact, it generated a question: If you had, say, a 350va UPS and extended its capacity this way, would you have to worry about overloading the charging system after the batteries are substantially drained? Or do most small- to mid-sized UPS use the same charging system and just a different size battery?The reason I ask is that I often see 300-400va UPS for around $30-40. If the charger in it works just as well as a 600-900va, then I'd opt for the generic battery extension to a small UPS instead of paying more for a bigger UPS that simply uses their bigger batteries.

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Now we're getting somewhere... When armed with the proper information, almost anything is possible :-)I was surprised to hear that the draw could be as high as 30 amps !!Would that be a system with 300-400 watt power supply, 17 inch monitor, CDRW, CD-rom, floppy drive ? Not driven by battery back up.... USB hub, printer, scanner , label printer, speaker amps, external cable modem.Jon, you say you have 33aH battery on yours and can run 60 mins ? What are YOU powering with this to last that long ?Thanks for the info, Staggerwing

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Hi again,1. Adding extra capacity vs. charging:If you increase the battery capacity, you generally increase the recharge time by a corresponding amount. "Standard" UPS recharge times are 8-12hrs with a fully discharged battery. Most small units only have a 0.8-1.2A charge rate (internally limited) so if you add lots of batteries to it, the recharge time from 'flat' can become quite long. You won't damage anything because the chargers are current-limited - it just takes longer. For my 7+7+7 solution mentioned earlier, you could expect a 24hr charge time. In any case, having a longer backup time means that you're less likely to fully discharge it. If it's real bad, just take the batteries out to the car and plug 'em into your cigarette lighter socket whilst you go down to the shops and back! DONT USE AN AUTO CHARGER - it'll kill your gellcells!2. Capacity vs. runtimeWorking out your possible runtime is quite easy. All you need to know is the power consumption of your PC! That is hard unless you have a 'power' analyser however I can give some guidance here.Allow 300VA for a single PC with a 15" monitor. 300VA at a 'power factor' of 0.8 translates to 240W (just run with me on this if you don't understand). A PC with a 17" monitor goes to 500VA (400W) etc. This is generally the most that the system will consume at startup. My home system draws over 500VA at startup yet consumes ~240VA running with the monitor.It is a Celeron running at 457MHz, two HD, two CD, 17" monitor.A 33ah battery can produce 396W/hr (12V x 33ah). I also have a 7ah battery inside the UPS making 40ah (480W/hr). If you allow for inverter efficiency (~85%), that's 408W/hr. My system draws 240VA (192W), so 408/192=2.125hrs. In reality, most batteries' capacity is quoted at a '10hr' rate. For discharge in 1-2 hrs, the capacity is almost halved so my 2.125hrs becomes about 1 hr.3. Current draw:30A? You bet! Take the 650VA UPS mentioned in the original postings:650VA > 500W. Assume 600W for the inverter (80% efficiency). At 12V, 600W = 600/12=50A(!). BTW, this is also part of the reason for APC using 12ah batteries - 7ah batteries are limited to about 30A. Many UPS >400VA use 2x 12V batteries in series to reduce current drain. My 6KVA UPS in the office uses 10x 12V/40ah batteries in series whilst a 40KVA unit may use 24x 12V/24ah in series - ouch!I know this sounds 'fudgy' but it works and I don't have to expose you all to a near-vertical learning-curve :-). If anyone has a specific issue, please email me and I can help. Jon Point*************************(effyouthree@hotmail.com)*************************

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It's good to have some advice from a real expert. Sorry for my somewhat half-baked advice earlier. Using a car battery seems like a bad idea. I mentioned it as this setup was widely used here in Taiwan after a heavy earthquake wiped out most of our power facilities; during the rebuild time most shops ran their cash registers and stuff from a UPS powered by a truck battery so they could stay in business:-) John, UPS batteries do seem to have a rather poor lifetime. Was my advice to give it a regular discharge-charge cycle correct or is there a better way to get the most out of your cells?Thanks for the high quality answers!Roland

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Thanks Jon. I still remember the old power factor from the old engineering classes but I didn't know about the 10hr rate. So, discharge in 1-2 hrs halves your capacity? What a bummer. I'll have to keep that in mind. Hot batteries have reduced effectiveness too so you don't want to bury them in some tight spot behind the desk.

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