RE: [pvusers] Need advice on using UPS as inverter

["Robert Warren" <robertwarren@mail.com>]

Chris,
 What is it you are really trying to do? First, you were trying to convert an inverter to 50Hz, and now you want to use a UPS as an off-grid inverter?
 Kirk is right about the UPS not knowing what the battery size is, except that from the software end of the APC Matrix 5000, you should be able to program it for a larger battery. (It is possible to buy these factory configured for a larger battery bank, but in this case, they provide a larger charger which is located in the external battery module). However, this will not help you in charging the batteries, as the battery charger is pathetically small and would take not just 60 hours, but easily over 100 hours to charge a 48 volt, 600 amp hour battery bank.  (Be aware that APC makes a number of different types of UPS's, some of which use a 120 VDC buss, not 48 VDC like the APC Matrix 5000.)
Also, make sure you completely remove all the internal batteries before you hook it up to a larger external battery bank, as old batteries hooked in parallel to a good set of new batteries may explode, and if not, will certainly ruin your new ones. It only takes one battery going bad in a string to screw up all the others. Typical APC UPS batteries are only 14 to 28 amp/hrs each, as I recall. 
  But the whole point of your search for an inverter is to marry it to a photovoltaic charging source, is it not? Why fool around with an AC charger, as finding a 48 volt charger that will be compatible to the UPS as well as the batteries can give you other problems, mainly due to compatibility of the high voltage cut-off points. Sealed batteries like a lower float setting than wet cells. Batteries do not care where their power comes from, it is like water filling up a lake. This power does need to be regulated, however, so it tapers off as the batteries become full and then to finally drop back to a current limited, float charge. This is the function of a PV charge regulator, and I would highly recommend the Morningstar Prostar PV controllers as a reliable and economical controller. There are a lot of other good ones out there, but this will also give you your voltage and charging current digital display. 
 I don't think that the APC products are the right match for transforming into a UPS, though. APC started out as an off-grid inverter manufacturer in the wind power market, and they have come a long way since then, but they haven’t made off-grid equipment for many years, now. But hey, if you only have $60.00 invested, it isn't a huge loss if you blow it up, which may well happen. Be sure you wear goggles anytime you are hooking up batteries. Always let the fused link be the very last thing you connect. Also, if you do have a grid source of power and do not dis-able the AC battery charger in the UPS, you need to install a filter cap to absorb the pulsed DC ripple effect of the charger, to protect the PV charge controller. This is also needed to protect the AC charger from the 10 or 20 kHz pulse of your PV charge controller. I did this once on a Best Ferrups UPS, which is a much more robust inverter than the APC ones. Not as efficient, due to the big ferro transformer, but they are bullet proof. 
 The next issue is how many PV modules and how much battery capacity? A good rule of thumb is to have a battery that will charge in ten hours from the PV system, so if you get 2 five hour days of sun, you are up and running again. You have to oversize your PV system by about 25% above that to allow for efficiency loss, plus you also have to allow for the fact that you may have your load running at the same time you are trying to re-charge your batteries.  Otherwise you are driving down the road with a leaky fuel tank and will be empty before you get home.  There are a lot of PV systems out there which don’t have a big enough PV array in relation to their batteries and the loads they have to support, so the batteries die an early death. If you are going to screw around with putting together a hodgepodge of used equipment, the very least you should do is to invest in a decent battery monitoring device, like the Trace battery monitor, the E-meter, or the Trimetric. 
 Yes, you do get a good sine wave from the APC products, though. I used to carry around a portable Fluke scope, and the waveform looks fine. I didn't like them as UPS's, however, as I found they didn't have nearly as much surge protection as the Best Ferrups UPS's. This is because they are line-interactive devices, so it is a completely different design architecture.
 One of your problems might be the auto sensing of 50 or 60Hz. You want this for use in Japan, didn’t you say? It will need to self-configure to 50Hz, which it would not be able to do if you use it as an off-grid device. But if you have 60 Hz appliances, then you are OK, as this is the default setting.  Another frequent problem with the APC products when connected to grid power is that minor fluctuations in input power will turn on the inverter and run down the batteries prematurely. This is what the UPS is supposed to do, though, as it does then give you a regulated power source for your computer. But, hey, it has been about 5 years since I worked on these things, so there may be changes in some of the features. Make sure you download the operating instructions and get the service manual, too.  Try http://www.apcc.com/resource/include/techspec_index.cfm?base_sku=MX5000&language=en&LOCAL.APCCountryCode=WW
 Yes, it is easy to pick up a good UPS rather cheap as the main thing is the batteries only last 3 to 5 years, and a lot of companies just throw them away. But unless you have an electronic background, I do not recommend trying to modify these things into home-made, off-grid inverters.  If is far better to put in a few extra hours, earn the money, and buy something that was made for the job.

Robert Warren
Senior Engineer, 
Solar Century Holdings, Ltd.
www.solarcentury.co.uk

----- Original Message -----
From: "kirk" <kirk@3rivers.net>
Date: Thu, 12 Sep 2002 21:05:19 -0600
To: "''Christopher Witmer''" <cdwitmer@spamcop.net>
Subject: RE: [pvusers] Need advice on using UPS as inverter 


> It sees a voltage source and has no idea what its capacity is. It doesn't know the size of the battery. This can be a problem if heatsink is
> inadequate and it relies on the battery being small enough that charge
> tapers and keeps thermal dissipation within available mass and surface area of sink. A large cell may keep charge too high for too long. Likewise time or duty cycle of operation may be too long for output heatsink if it is designed for 45 minutes at max power and you want to run it for hours and can with large bank.
> 
> Hard to believe a pure sine for $60.
> 
> Kirk
> 
> -----Original Message-----
> From: Christopher Witmer [mailto:cdwitmer@spamcop.net]
> Sent: Thursday, September 12, 2002 4:22 PM
> To: pvusers@crest.org
> Subject: [pvusers] Need advice on using UPS as inverter
> 
> 
> In Japan I have been having a very hard time finding an affordable DC-AC
> inverter; however, it isn't hard to find a large UPS that needs
> batteries. For example, I just found a used APC Matrix 5000 (a pure sine
> wave unit) now being sold for the equivalent of about $60. (This
> particular unit is being sold without batteries.)
> 
> This UPS is designed to work with any number of add-on battery packs,
> each 48v/17ah. (APC calls these "Smartcell" batteries and of course they
> have a multi-wire connector of a unique design.) Instead of the
> manufacturer's recommended battery packs, I want to use one BIG 48v
> battery string -- e.g., something in the range of 600-1000ah.
> 
> I imagine I will have to overcome two obstacles: 1) to get the inverter
> to accept a different battery than it expects, and 2) to recharge the
> battery string without using the inverter's built-in recharge function.
> (It takes eight hours for this UPS to recharge 10 battery packs -- just
> 170ah. That means it would take 35-60 hours to recharge the large
> battery string I'm contemplating.)
> 
> I have access to a separate charger for the batteries, but does anyone
> care to speculate how easy it will be to get the inverter to accept my
> large battery string and function as I require?
> 
> Basically, I'm worried that the UPS might have some built-in self-test
> function and when it detects that something is not just as expected, it
> will refuse to function at all, and I won't be able to override or work
> around that.
> 
> Any thoughts? Thanks!
> 
> Christopher Witmer
> 
What will we do if there is another fuel shortage? 
Did you know that there is a pollution free, completely renewable fuel which you can use right now in your own car? 
Don't replace the engine, replace the fuel. Check out my website on making your own fuel: 
http://running_on_alcohol.tripod.com 
robertwarren@mail.com

-- 
__________________________________________________________
Sign-up for your own FREE Personalized E-mail at Mail.com
http://www.mail.com/?sr=signup


--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*
  List sponsored by CREST/REPP  
	http://solstice.crest.org/   http://www.repp.org/