can extra chargers be used with inverters

lexington · August 2014

Can an intelligent extra charger be connected WITH an existing inverter to the same battery bank, without any of the two going up in smoke? Here are the facts:
1. Existing inverter: 48V/5KVA, low frequency, with inbuilt charger of 35amps.
2. Extra charger: intelligent 3- stage, 48V/50A charger, MCU controlled, fan cooled.
3. Battery bank: 48V/1600AH composed of 32 pcs of 200AH/12V AGM, lead acid battery. (4 X 8 batteries, 8 strings in parallel)
4. There are 5hours of utility supply per day, mostly at night. The idea is to increase charging current and AH supplied to batteries at night for use in the day time.
5. Current estimated load AH consumed per day: 511AH.
6. Combined C/Rate: 35+50 = 85amps, which is better than the existing 35A, but less than the C/10 of 160A.
7. Can this method of adding extra chargers be used in all other cases of insufficient charge by the inverters?

Hope to resolve the issue BEFORE anything is purchased. Will this be a solution practically?
Thanks to everyone.

Cariboocoot · August 2014

Re: can extra chargers be used with inverters

Welcome to the forum.

Yes battery banks can be connected to more than one regulated charge source at the same time. Most chargers use Voltage to regulate and all they see is 'X' Volts on their terminals; they don't know or care that some of it is coming from another charger. The trouble comes if the combined output current of the multiple chargers can exceed the safe maximum for the batteries.

Now about that battery bank. Thirty-two 12 Volt batteries on a 48 Volt system. That means eight parallel strings of four. No way is current being shared evenly on so many strings even if it is wired "perfectly" (equal length wiring to positive and negative bus bars).

1600 Amp hours @ 48 Volts is a whopping 38kW hours @ 50% DOD. Why on Earth is there so much battery? You would need 160 Amp potential to properly charge that and that isn't coming from a 35 Amp built-in charger plus an external 50 Amp charger. That battery bank is doomed and if it's been in use for very long has probably already suffered greatly. Is there any solar charge source on this?

Load estimate of 511 Amp hours (24.5 kW hours) per day. If I were you I'd be measuring that as precisely as possible and making a concerted effort to reduce consumption. Some of that battery may not be doing much, meaning the rest may be doing too much.

Finding really large chargers for 48 Volt systems is difficult unless you go with commercial units. At the required current here that may be necessary. Otherwise it might be worthwhile to change the inverter for one that has a more robust built-in charger. An Outback Radian, for example, puts out 115 Amps.

Even then I think that battery bank should be thoroughly tested (not easy with AGM's) and probably replaced with fewer, higher capacity units (if indeed that much stored power is needed).

BB. · August 2014

Re: can extra chargers be used with inverters

Welcome to the Forum Lexington.

Short answer, yes, you can put several chargers on one battery bank. They will not cause any physical problems. I recommend that your "home run" each controller back to the battery bank--Each with its own fuse/circuit breaker (to protect wiring against short circuits).

You may have other issues here... You only have ~5 hours of power per night to recharge your battery bank? That is getting to be a pretty short time to fully recharge a lead acid battery bank. If you assume that you need a minimum of 2-4 hours of absorb (holding battery at ~58 volts), that only leaves a few hours to "bulk charge" (getting full current from charger into battery bank).

Lets guess that you need 511 AH (at 48 volts) and 2 hours of absorb and 3 hours bulk. And that most of the energy will be returned during bulk:

511 AH / 3 hours of bulk charging = 170 Amps of charging current from charging sources minimum

Your 1,600 AH @ 48 volt battery bank is really large--And using 4 parallel strings of AGM will need you to monitor its performance very closely. You will want to have "balanced wiring" (like #3 in link) between strings. And have a DC Current Clamp meter so you can measure current flow in each battery string current during charging and discharging (once a week to once a month--To ensure that wiring is good and no battery cells are failing shorted or open circuit).

If you have the batteries brands/models available, I would be suggesting that you get larger AH rated batteries and get to the range of 1-3 parallel strings of batteries (I really like 1 or 2 parallel strings if possible).

You can easily justify charging at C/10 to C/8 (10% to 13%) rate for solar, and for AC charging, you can go 20 to 25% rate of charge--If you can get a charger that monitors battery bank temperature--That would be great too. Otherwise, keep track of battery bank temperature. High temperatures shorten battery life (every 10C increase, life is reduced by 1/2) and can have thermal runaway (At C/8 rates of charge, batteries can become hot. And hot batteries reduce their charging voltage--Can lead to thermal run away).

AGM batteries do have lower internal resistance, so they can supply/accept higher current levels vs flooded cell.

Lastly, but really should be first--Have you addressed your loads and done pretty much anything you can to conserve energy usage? In general, it is almost always cheaper to conserve power than it is to generate power.

Also, battery backed systems for shifting power usage (charge at night, use battery power during the day) does have losses. To use some typical (conservative) numbers:

90% battery efficiency
80% charger efficiency
85% inverter efficiency
Overall efficiency = 0.9 * 0.8 * 0.85 = 0.612 = 61.2% end to end efficiency
1/0.612 = 1.63 = ~63% more AC line energy needed to run system.

Any thoughts/questions?

-Bill

Photowhit · August 2014

Re: can extra chargers be used with inverters

lexington wrote: »

Hope to resolve the issue BEFORE anything is purchased. Will this be a solution practically?

Yay you!

You want to put 85Amps for 5 hours = 425 Ah into a battery bank daily and take 511Ah out...on average? That's a no brainer, are you not telling us something? other sources of charging?

8 Strings is NOT realistic as others have said. You can get a 48v 1600Ah traction battery if you have a place to put it 4000lbs, it will not be maintenance free. Your looking for a 24-85-25 24 cells, 85amps per positive plate(6 hour rate), 25 plates (12 positive)

Multiple charger should not be a problem, up to the designed charging max for a system this size, some small inverters might find higher battery voltage a problem, but I doubt you'll find a 48v that will have a problem with this.

vtmaps · August 2014

Re: can extra chargers be used with inverters

lexington wrote: »

Can an intelligent extra charger be connected WITH an existing inverter to the same battery bank,
<snip>
2. Extra charger: intelligent 3- stage, 48V/50A charger, MCU controlled, fan cooled.

Generally, yes you can hook up as many chargers as you wish. BUT, maybe it won't work.

It depends on how "intelligent" the charger is... some chargers when first turned on go through a routine to evaluate the battery and will not work properly if the battery is connected to another charger.

Some chargers do not use the standard RE bulk-absorb-float protocol... if the charger uses a constant current protocol it will be confused by other chargers or loads. An example would be a forklift battery charger... the forklift is being charged with no load on the battery and no other charging source. Some automotive chargers do the same thing... they expect that the car is not being driven while charging.

RE charging protocols work very well with multiple charging sources... as long as they all use the same protocol.

What intelligent charger are you thinking of?

--vtMaps

Vic · August 2014

Re: can extra chargers be used with inverters

And, often, external battery chargers do not measure the battery temperature, and compensate the charge voltage according to the measured temperature. In addition to all of the very good reasons to NOT run parallel battery strings, is, that with many, many smallish batteries, there is no good place to mount a Battery Temperature Sensor -- the large area needed to place all of the batteries often has temperature variations. In addition, unequal current sharing, especially during charge will cuase some batteries to be warmer than others. AGM batteries are very sensitive to the exact charge voltage, as has been noted.

Also noted, previously, is the fact that the Inverter/Charger that you are considering has a very low charge current capability vs its claimed power output capability. If you really need as much power delivered from the batteries that you have noted, you will NEED a much more capable inverter/charger to charge the batteries from AC power, IMO.

It IS very good that you are asking about your envisioned system before anything has been purchased. Many times people join this Forum to ask advice on how to use inappropriate/unmatched components.

Just opinions. Good Luck, Vic

zoneblue · August 2014

Re: can extra chargers be used with inverters

If you use 500Ah per day, and the bank can reliably be recharged overnight, you ought to be able to reduce the bank to about 1000Ah, yeah plus a bit for efficiency.... 50% DOD daily is working it reasonably hard, but probably most cost effective. Your using 26kWh per day, that is kind of up there, national average in my country. Id be looking at shifting some loads to propane if possible, easier and cheaper to store than electricity. If your recharge is eratic, then i see why you need 1600Ah. But you do need lots more battery charger whatever you do. AGMS need even higher charge rates than flooded to keep things stirred up. Cant EQ or do long absorbs like FLA. This sounds like a good application for LiFePo4 or traction FLA with thier 80% DOD range.

lexington · August 2014

Re: can extra chargers be used with inverters

thanks for all the inputs from members here is the latest update:

1. i am trying to reduce the load consumption to around 255AH.

2. the supply is epileptic in my country, especially where the system is located is usually 6hours of light, it MAY be more, but one cannot count on that. that is the problem and the reason why the battery bank is large. it was meant for use when those 6hours of light are given at night BUT not during the day.

3. the largest battery capacity available here is 200AH, AGM. higher capacities not on sale.

4.the external charger i checked out in our capital city is available in two voltages, 48V/100amps and 96V/50mps., it claims to have 7 stage charge, absorb, recharge stages. i am trying to upload the charger manual, can't seem to find out how.

5. based on your advice, can the 48V inverter be changed to a 96V one and the battery set reconfigured to 800AH/96V, this will be 4 strings instead of 8 before. i think this will afford more uniform charge of parallel strings.

6.The 96v inverter has 25AMPS inbuilt charger. Based on load use, the battery will not be drained per load cycle. a member mentioned an OUTBACK RADIAN INVERTER? any link on how to get this?

7. if the load profile is reduced, will 25amps inverter charge current not cause problems of under-charging since it is less than the c/10 rate of 80A? my aim is to reduce the load consumption to only what the chargers can refill per day (every 6 hours). i am suggesting that generators be used to augment the supply if the utility supply is insufficient.

thanks for advice in advance.

BB. wrote: »

Welcome to the Forum Lexington.

Short answer, yes, you can put several chargers on one battery bank. They will not cause any physical problems. I recommend that your "home run" each controller back to the battery bank--Each with its own fuse/circuit breaker (to protect wiring against short circuits).

You may have other issues here... You only have ~5 hours of power per night to recharge your battery bank? That is getting to be a pretty short time to fully recharge a lead acid battery bank. If you assume that you need a minimum of 2-4 hours of absorb (holding battery at ~58 volts), that only leaves a few hours to "bulk charge" (getting full current from charger into battery bank).

Lets guess that you need 511 AH (at 48 volts) and 2 hours of absorb and 3 hours bulk. And that most of the energy will be returned during bulk:
511 AH / 3 hours of bulk charging = 170 Amps of charging current from charging sources minimum

Your 1,600 AH @ 48 volt battery bank is really large--And using 4 parallel strings of AGM will need you to monitor its performance very closely. You will want to have "balanced wiring" (like #3 in link) between strings. And have a DC Current Clamp meter so you can measure current flow in each battery string current during charging and discharging (once a week to once a month--To ensure that wiring is good and no battery cells are failing shorted or open circuit).

If you have the batteries brands/models available, I would be suggesting that you get larger AH rated batteries and get to the range of 1-3 parallel strings of batteries (I really like 1 or 2 parallel strings if possible).

You can easily justify charging at C/10 to C/8 (10% to 13%) rate for solar, and for AC charging, you can go 20 to 25% rate of charge--If you can get a charger that monitors battery bank temperature--That would be great too. Otherwise, keep track of battery bank temperature. High temperatures shorten battery life (every 10C increase, life is reduced by 1/2) and can have thermal runaway (At C/8 rates of charge, batteries can become hot. And hot batteries reduce their charging voltage--Can lead to thermal run away).

AGM batteries do have lower internal resistance, so they can supply/accept higher current levels vs flooded cell.

Lastly, but really should be first--Have you addressed your loads and done pretty much anything you can to conserve energy usage? In general, it is almost always cheaper to conserve power than it is to generate power.

Also, battery backed systems for shifting power usage (charge at night, use battery power during the day) does have losses. To use some typical (conservative) numbers:
90% battery efficiency

80% charger efficiency

85% inverter efficiency

Overall efficiency = 0.9 * 0.8 * 0.85 = 0.612 = 61.2% end to end efficiency

1/0.612 = 1.63 = ~63% more AC line energy needed to run system.

Any thoughts/questions?

-Bill

vtmaps · August 2014

Re: can extra chargers be used with inverters

lexington wrote: »

the largest battery capacity available here is 200AH, AGM. higher capacities not on sale.
<snip>
based on your advice, can the 48V inverter be changed to a 96V one and the battery set reconfigured to 800AH/96V, this will be 4 strings instead of 8 before. i think this will afford more uniform charge of parallel strings.

Four strings is still too many... more so with AGM than flooded batteries. I don't know where you are located... if you can't get the sort of battery that you need, then maybe you can't do what you want to do. There may be other solutions... can you break up the system into multiple smaller systems?

--vtMaps

lexington · August 2014

Re: can extra chargers be used with inverters

i'm located in Nigeria. nobody wants to maintain flooded batteries. they prefer AGM's / VRLA's. breaking into smaller systems? they specifically asked foe a single unit. inverter used in previous system did not work from day it was installed and handed over. contractor not available any longer. trying to see what best can be done to provide adequate backup for systems connected to the computer. the load is this:

10 desktop pc's with flatscreen monitors
2 flatbed scanners (25WATTS)
i central server printer HP LASERJET 3020 (660watts)

the desire is to have 8 hours operation per day. that's why the battery bank installed was large. the objective is to put batteries back in use. thanks.

Cariboocoot · August 2014

Re: can extra chargers be used with inverters

Ouch. Ten desktop computers can suck down a lot of power. 150 Watts each easily. The trouble is it will vary depending on which ones and how they are being used. It may be 90 Watts or less sitting idle and 200 Watts running 'full out'.

If you estimate 150 Watts on average X10 plus the two scanners @ 50 Watts and the printer @ 660 (might actually be higher) you've got 2210 Watts running for 8 hours or 17,680 Watt hours. That's about as much as a household uses in 24 hours.

If we divide that by 48 Volts we get 368 Amp hours consumed, meaning a minimum battery bank of 737 Amp hours. The trouble is that first variable is a big one. This is probably why the batteries were sized at 1600 Amp hours: 25% of that is 800, 'sized up' from my 737 estimate. It makes sense.

So the question is: can the battery bank be safely reduced to half size? What will happen if the power goes down? If this is a 'do or die' situation then having two redundant systems becomes even more logical. I'm not sure what the budget is, but if you go cheap on a project like this you will also go shoddy and it won't work. Which is what you've got now.

You may be stuck with 200 Amp hour batteries, but maybe not with eight strings of them or perhaps not all together. Hopefully you're not stuck with one inverter. Or at least not with the one you've got which doesn't appear to be very good.

In Nigeria you use 230 VAC 50 Hz power (I think). That means you could look at Outback export models http://www.solar-electric.com/inverters-controllers-accessories/inverters/ouin/oupoinoffgrb.html and possibly stack two of them (140 Amps charging, 6kW output potential). Victron may also offer something suitable: they are well-liked overseas but not common in North America where we are. I don't see any mention of a Euro standard Radian, but the Conext XW series is available in 230 VAC 50 Hz version. Also check out SMA's Sunny Island offerings.

lexington · August 2014

Re: can extra chargers be used with inverters

thanks.
yes in Nigeria the voltage is 220Vac/50hz. the problem is the insistence for a single inverter, sized at 5kva. so my suggestion was to be:

1. get an inverter rated for 96V.

2. my intuition tells me that inverter will only be used sparingly, as efforts are being made to get more stable power supply that will last more hours, AND give more charge over time.

3.the desktop systems are only used for running custom data management software.

4. well 4 strings of 8 batteries in series at 96V IS better than 8 strings, not so?

5.printer usually used heavily only when reports are prepared at end of the month or quarterly.

6. if a 96V/50Amp commercial charger is bought in addition to the 25Amps from the inverter will it make the system more reliable?

they are asking for systems that can be purchased locally in case of problems or warranty issues, but i will explore the inverters you suggested and try and convince them based on your advice and inputs here.

i have learned a lot. thanks.

Cariboocoot · August 2014

Re: can extra chargers be used with inverters

I'm thinking what you really need here is a commercial UPS unit. They use higher Voltage battery banks and are designed to do exactly what is required: back up power computers so they don't go down. They are not cheap and are outside the realm of our forum, but a couple of the members (Techntrek?) here use them I believe.

lexington · August 2014

Re: can extra chargers be used with inverters

hi,
i actually measured the consumption of the printer when printing via a digital clamp meter, and 660 watts was reading. when not printing consumption is low.

i believe you are referring you the VFX3048 OUTBACK? will it be ok to split batteries into 2 separate banks? 4 strings per inverter? will that be ok?

thanks for your prompt response.

thanks again.

lexington · August 2014

Re: can extra chargers be used with inverters

thanks,
the inverter or so-called ups unit i met there was a 30kva, 108V unit. strangely when the cover at the back was opened, i was amazed at what i saw:
72 pcs of 12v/7Ah batteries as used in common 650VA bluegate UPS units!!! how was that supposed to back up, even 5 desktop pc's?

32pcs of 200AH/12V were purchased under advice of initial contractor.

that is why, i hope that 2 separate 48V inverters or 1 unit of 96V inverter may be used instead to power up the batteries. i believe that the inverter will be used sparingly when their is an outage just to keep work going. they are trying to minimize diesel costs.

thanks again
.

Cariboocoot · August 2014

Re: can extra chargers be used with inverters

lexington wrote: »

hi,
i actually measured the consumption of the printer when printing via a digital clamp meter, and 660 watts was reading. when not printing consumption is low.

Laser printers can have a high demand heating up the fusing element. It varies with the printer and how often it heats, so the 660 Watts may be accurate or only averaged.

i believe you are referring you the VFX3048 OUTBACK? will it be ok to split batteries into 2 separate banks? 4 strings per inverter? will that be ok?

thanks for your prompt response.

thanks again.

If you couple the AC outputs of the FX inverters you must also couple the DC inputs. So in that configuration there would still be eight parallel battery strings, but two inverters to charge them all from.

If you separate the AC outputs of the FX inverters the DC inputs do not need to be coupled and each would have four parallel battery strings which is not a problem on 48 Volts. When you do this you must wire some outlets to one inverter and some to the other, and remember which is which in case you have to switch loads between them.

lexington · August 2014

Re: can extra chargers be used with inverters

thanks,
the desktop pc's are in separate offices and i believe they can be isolated in groups, even though it would be pretty tedious to work through the surface trunking used to power the systems. the computers were placed on a different wiring from the rest of the building and they only are placed on the inverter back-up.

sorry to ask again: if 4 strings are ok for 48v inverters, are they ok for 96V?

i am trying to assimilate all you have said, and trying to match it to available resources and inclination of management. i will let paste on the forum a progress report as things develop.

thanks, again.

BB. · August 2014

Re: can extra chargers be used with inverters

I would look very closely at the computers (and other power usage)...

I know that laptop computers are very expensive in other parts of the world (they are getting pretty cheap here)--But depending on software/needs and even more efficient desktop computer power standards--You can drop that 150-200 Watts to 30 watts or even less pretty easily with laptop/better choices in hardware (for example, if Linux, use any of the large numbers of small computers out there like Raspberry Pi or similar). Modern LCD monitors can use much less power too.

Most computers are much larger (more memory, faster processors, etc.) than many people can really use. If just doing standard data processing, less powerful machines and/or turning down clock speeds (if configurable on your machines) can help a lot. If you need lots of processing power (servers, lots of computations) or need configurations (run Apple or PC applications), you may be stuck with high power usage.

Also, if you have a warm/hot climate--Dumping 10x150W=1.5kWatts of heat into your building vs 10x30w=0.3 kWatts of heat into the building can reduce A/C and/or circulating fan needs too.

Laptops also have built in batteries--So UPS needs can be greatly reduced too (i.e., short power hits will not reboot your computer--Gives you time to start up a genset and/or use a less sophisticated UPS system.

-Bill

lexington · August 2014

Re: can extra chargers be used with inverters

thanks,

changing to laptops was my initial answer to large consumption of the desktop pc's. their reply was that staff were more inclined to take the desktop pc's for private use and then, not return them when disengaged from service. desktops were less prone to such " appropriations".

the PC's are relatively new, not core i3 or the such, mostly duo core, i think. 150watts seemed a reasonable estimate of power consumption.

like you rightly said, there are fans installed in every room.

i'll have to make do with systems as they are, that is why i joined the forum: get the best advice to manageably use the resources available.

thanks for your advice.

BB. · August 2014

Re: can extra chargers be used with inverters

Since you have so many PCs... I wonder if you can justify building one more low power version. Getting a low power mother board (some are supposed to be less than 6 watts for the bottom end--probably not enough for your needs--But...) and experimenting.

http://www.silentpcreview.com/Intel_DQ77KB_mITX

You have a Current Clamp meter--So you can monitor power usage with your experimental system and have something to roll-out as you can justify (or even possibly do a mother board swap in the existing systems).

I know the issues of laptops walking... Years ago in the US, it was assumed that the average corporate laptop had a "useful life" of about one year (stolen, dropped, fell off roof of car, etc.).

I would suggest you look at your costs to provide clean/reliable power (capital costs for equipment/installation, ongoing maintenance, etc.)--And see if you can reduce your power needs by 2/3rds (example) if the UPS/Power System savings can be channeled to more energy efficient equipment.

See if you can buy a kWatt*Hour meter to do some testing... Existing power usage numbers (and cost of power/cooling/etc.) may help your economic case too. There are 220 VAC 50 Hz versions of Kill-a-Watt type meter too:

Kill a Watt 230 VAC / 50 Hz

-Bill

zoneblue · August 2014

Re: can extra chargers be used with inverters

96V inverters are somewhat rare. None of the main off grid manufacturers make one. We keep asking, and they keep saying its too hard. Thats not to say they dont exist, some companys make specialied inverters for electric cars which can be 120V or so. Really depends on what you can get where you are.

While multi batt strings isnt ideal, and you didnt hear this from me, but lots of people do it, and get away with it. The important thing, Id be adding as much battery charger as you can afford to get the charge rate somewhere in the 20% C range (AGM only). That will allow a full recharge in 7 hours. To maintain the batt strings, you need breakers on each string, exactly equal length cables to each string, and twice annual string balance inspections.

can extra chargers be used with inverters

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