which charge controller for my... custom UPS system

System

at first, you may think that i am in completelly wrong forum/site, but i am not. please keep reading.

i have a need for a UPS with relativelly high capacity. UPS devices that i had:

• had capacity to run my equipment for less than 10minutes
• were unreliable - sometimes relays does not switch fast enought and power for computers is cut.
• relativelly high cost for new battery (keeping in mind its such a low capacity)

i had come up (long time ago) with an idea to build my custom UPS system, like online UPS. the key ideas:

• use old car batteries connected in parallel (maybe separated with diodes)
• avoid voltage converters (aka inverters) where possible

so, i (intend to) use:

• efficient power transformer ~220V to 12V [already running toroid transformer 12V 37.5A]
• use special ATX PSU that requires 12V input instead of ~220V [already running]
• connect network devices (switch, access point) directly to 12V
• connect lights - luxeon star rebel LEDs (2160lumens, 30W) [already running]
• charge controller [need advice]

the remaining unsolved issue is charge controller. i do not need powerfull one because:

• i do not need fast recharge - the main purpose of the system is to act as UPS - input (mains) power is available most of the time
• i need to connect high current load (up to 25A), but i will connect it directly to battery (not to output of charge controller) because i do not need discharge protection (first - complete discharge is unlikelly; second - i risk only some old car batteries).

therefore in worst possible case i could use as weak as 1-3A charge controller.
actually i plan to buy a 10A one because i want to be ready to connect solar panels up to 10A in case i get some in near future (currently i have (made by myself) a 5W panel - i think it is pointless to try to connect here such a small one).

i am searching at ebay. the problem is that most sellers do not provide (they do not know) enought information... the characteristics that i miss most of the time are:

• is it a dumb relay (i have really seen those) controller or PWM
• what is the minimum input voltage for controller to begin charging? with normal load connected the voltage at the transformer output sometimes drops even to 13V
• is it efficient enought
• can it be used outdoors
• some units have certification marks like "CE" - in those cases i could infer that units have filters (to filter out noises created by PWM) and other stuff. but others seem to be manufactured in unknown "garage"..

so, considering the requirements i mentioned, could anyone recommend me a charge controller?

i am looking at these:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230457477592&ssPageName=STRK:MEWAX:IT
--- does not have certification marks. unknown manufacturer.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280412826498&ssPageName=STRK:MEWAX:IT
--- relays, PWM?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230458246016&ssPageName=STRK:MEWAX:IT
--- relays, PWM?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270555312622&ssPageName=STRK:MEWAX:IT
--- looks good

what do you think?

and also... can you see any critical mistakes in my design?

thank you

BB.

Re: which charge controller for my... custom UPS system

As long as your 220/12 volt converter outputs a reasonable float voltage for the battery bank (around 13.5 volts or so) and is able to handle your DC loads (computer + lights + etc.)--You appear to be OK (you should have fuses/breakers between the battery bank and your various loads/charging sources to help prevent fires).

I don't think you need any diodes on the battery bank.

Obviously, car batteries are not ideal for deep cycling--but as a standby power source for your UPS--they probably will work OK if treated properly.

Most "standard" DC power supplies/chargers have a mode where if the battery voltage falls below ~13 volts, then the charger steps up to ~14.2 volts or so to quickly recharge the battery bank back to full charge, then drop back to 13.5 volts for "float" charging--just enough voltage to keep the batteries fully charged).

Regarding the solar panels--I am not sure why you would use them at all unless they are fairly large (at least equal to your load current/power). And if you where going to run your DC loads from your solar panels, they should be something like 5x your average load (assuming 4 hours of "full sun" per day)... Probably not economically practical for your use.

Instead, you may wish to simply use a generator as backup power for your 220/12 charger instead for longer term power outages.

-Bill

niel

Re: which charge controller for my... custom UPS system

if you are doing an ups arrangement then why are you looking at charge controllers or do you intend to add photovoltaic panels too?

it sounds like you are trying to reinvent something that already exists. it's called an inverter/charger and will automatically trigger in an outage. you may get away with using modsine which is cheaper as pcs aren't that picky about waveform purity. i'm not all that familiar with what's available for your voltage and frequency, but i know they are out there. btw, these are usually hardwired and fused.
as to the batteries, do not use car batteries as these are purely for starting vehicles with high short bursts of current. you need deep cycle and many use the 6v type used in golf carts and wire enough of them in series to achieve the proper voltage for the inverter. most operate at 12v, 24v, or 48v and if higher voltages are used it saves in wiring to a point. you need to know what your loads need in watts over say a day and many get a meter like the killawatt to measure the watt hours over a day.
http://store.solar-electric.com/kiacpomome.html
if you find a reasonable inverter without a charger then you may use a separate charger. is this the reason you want a controller is to make a charger out of it?

System2

Re: which charge controller for my... custom UPS system

BB. wrote: »

Regarding the solar panels--I am not sure why you would use them at all unless they are fairly large (at least equal to your load current/power). And if you where going to run your DC loads from your solar panels, they should be something like 5x your average load (assuming 4 hours of "full sun" per day)... Probably not economically practical for your use.

solar panels for me is an exotic part at the moment. my thinking was like: from environment perspective, better to use at least some of them than none.

BB. wrote: »

Instead, you may wish to simply use a generator as backup power for your 220/12 charger instead for longer term power outages.

long term power outages are unlikelly. i calculated that batteries will have enought capacity to power my devices during outage.

System2

Re: which charge controller for my... custom UPS system

niel wrote: »

if you are doing an ups arrangement then why are you looking at charge controllers or do you intend to add photovoltaic panels too?

i intend to use PV panels in future...

niel wrote: »

it sounds like you are trying to reinvent something that already exists. it's called an inverter/charger and will automatically trigger in an outage. ...

yes, it may look like i am reinventing a wheel.. but (i think) i am not.
first, i have already mentioned disavantages of using generic UPS systems targeted to mainstream custommers. like efficiency. i don't like the idea of using inverters - they are energy hogs. 12/220 inverter waists some energy when stepping up voltage, then load (like computer) waists energy again converting voltage back down. i mentioned other disadvantages also.

but it is a little unclear to me what exactly did you mean by saying "it's called an inverter/charger"? did you mean the whole generic UPS systems/devices, or something else like controller circuit boards?

thank you

porkfarm

Re: which charge controller for my... custom UPS system

I am in the same boat as you, I have a large battery bank that I want to float charge. I have access to a bunch of used APC UPS units that are used for racked computer systems.

Instead of buying the 2100 dollar inverter charger that I should use ( magnum that I think solar can also be worked in.), I figure these APC units are already inverter chargers. 5000 has a 3574 inverter with 208V and I have a 1000 that is 110V.

From all the research I have done, I think it is key that the charger be a tapper charger that can be on all the time as the float volts breaks down to the perfect charge rate of 2.23 - 2.27 per cell. Anything higher/lower than that and the batts get harmed. But that is for my ABSOLYTE IIPs . If I use a charger that has a bulk, I think I risk harm. IOTA seems to be the charger of choice for my 48V bank. Check out some of the specs @ the store on this website.

If these APC's don't work out, that's where I am getting my IOTA..:D

niel

Re: which charge controller for my... custom UPS system

a computer back ups is different than an inverter/charger as these are made for continuous duty unlike those made for pc shutdowns and you will find higher power levels accommodated by a single inverter. i will cite an example of one, but it is not necessarily a recommendation that you obtain that particular inverter/charger.
i refer to the magnum export modsine inverter/chargers.
http://www.magnumenergy.com/MM-Eseries.htm
clicking on the pdf data sheet shows the specs. power levels need to be determined that you'll need and if you elect for sine wave then these don't qualify in that area and you'll need to search for that type. again this is an example and i'm sure these are not the only ones out there.