Disconnecting charge controller after bulk phase?

If I have 4 FM80 Charge Controllers used for rapid charge during the bulk phase but due to battery limitations I can only have the current from 1 of the 4 Controllers during the absorb phase (higher vpc rate).

Is it possible to have 3 of the 4 shut down via the charge controller settings, i.e, not have them enter the absorb phase, or would I have to have an external (AUX) switch to disconnect 3 of the 4 once the Absorb voltage set point is reached?

Or Can all 4 keep running but limit the output to the equivalent of 1 of the controllers once the absorb voltage set point is reached?

Reading the operating manual for voltage set points doesn't seem to answer this for me.

Thanks.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    Please do not take offense, but this set-up doesn't make sense.

    First of all, the output from an FM80 is up to 80 Amps at any system Voltage. Four of them could push out 320 Amps in parallel, if you have enough panel to drive them all. For any size system, this would be in the realm of a megabank of battery. Otherwise you're pushing the charge too fast.

    Secondly, once Absorb Voltage is reached it stays there; current is reduced so that the Voltage level is maintained. It wouldn't matter how many FM80's were attached: if they're all programmed alike, they'll all respond alike.

    Thirdly, if you've got four you either have to have four RTS units or else (and this is a really good idea with this many units) have all the charge controllers communicate through an Outback Hub and controlled by a MATE.

    May I ask just what sort of system you've got in terms of battery capacity, array size, system Voltage, and inverter? I've never encountered anyone needing 320 Amps of charge current before. I'd suspect you have a massively over-sized bank on a 12V system when you should be going up in Voltage to supply the power requirements.

    I don't mean to be mean, but the idea of having four FM80's just floored me! :D
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Thanks for the reply.
    Yes don't take the hypothetical scenario as gospel.

    I think you answered my question when you said that they 'reduce their current' to stay at the absorb vpc point.

    Lets say the max charging amps a certain 48 v battery bank is 47 A in the absorb phase. During the bulk phase they can be charged at 275A providing the vpc point is at 54v i.e. lower to avoid heating issues and damage to the batteries.

    So I was thinking that if all '4' (or 2 or what ever produces more than 47A pending array size and config) where putting out 47 x 4 = 188A (under the 275A limit) then when the lower voltage setting for the beginning of the absorb phase it reached (54v), then they would all continue to put in more current than the 47A limit...... The 47A is per string, so I could increase the battery strings to allow more current but in this example that is not possible.

    With what you are saying; the 4 controllers would reduce each of their outputs to keep at the lower set point for the rapid bulk charge below that 47A limit?? So this absorb phase would just continue until the battery is full then go into float?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    Okay you may have got hold of some confused information about charging phases. Maybe you should review this part of he battery FAQ first:

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery%20Charging

    When you're setting up a system, the charge current rate is set as a function of the battery bank size. In other words you plan for 5%-13% of the Amp/hrs to be the peak current. The most current will flow during the BULK phase. In the ABSORB phase Voltage is held at a predetermined level, and current fluctuates. FLOAT functions the same way, only at a lower Voltage because you're not 'replacing Amp/hrs'.

    If you try to charge batteries at too high of a rate they will fry. Or 'boil' might be more accurate, as the water in the electrolyte solution will be 'gassed off' as it turns into hydrogen and oxygen. This is something to avoid. The excess heat and (possibly) exposed plates can lead to a destroyed battery in one go.

    That 320 Amps I mentioned the four FM80's can supply? That's enough for 3,200 Amp/hrs. On a twelve Voltage system that's roughly 19 kilowatt hours. On a 48 Volt system it would be 4 times that: 76 kilowatts.
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    47.6 amps is 20% of the 6hr rate for the battery bank. 275 is the max they can handle providing the vpc is at 54v i.e so it cuts off before it 'boil's the battery bank.

    These figures are straight from the manufacture and also discussed directly over the phone and email to their engineer.

    I just want to know how you can configure the settings (cutoff points,triggers) of the charge controllers to ensure that output from the charge controllers is at the MAX current limit (potentially 275A), ONLY during the bulk phase and then reduces to the 47.6amps for the Absorb phase...?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?
    solarabcd wrote: »
    47.6 amps is 20% of the 6hr rate for the battery bank. 275 is the max they can handle providing the vpc is at 54v i.e so it cuts off before it 'boil's the battery bank.

    These figures are straight from the manufacture and also discussed directly over the phone and email to their engineer.

    I just want to know how you can configure the settings (cutoff points,triggers) of the charge controllers to ensure that output from the charge controllers is at the MAX current limit (potentially 275A), ONLY during the bulk phase and then reduces to the 47.6amps for the Absorb phase...?

    When we talk about charge current in RE we are usually referring to the battery's 20 hour rate, not the 6 hour rate. What batteries are these?

    There's no worries here; ABSORB is governed by Voltage, not current. There is also programming capability to limit time (min and max) and to have the cut-off be determined by current level (drops to float if current falls below a certain level).

    You can read the whole FM80 manual here: http://www.outbackpower.com/pdf/manuals/flexmax_80.pdf
    (Always a good idea before you spend the money! :D )

    I have to say this sounds like a most unusual, and therefor interesting, system you're working on.
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Yes I was surprised they used the 6hr rate rather than the 20 too but it is 20% of the discharge rate in amps at the 6hr rate, which is 238A x 20%=47.6A).

    This works out at around 2-3% of the full 20hr rate (1808AH). The 275A for bulk charge works out at about 15% of 20hr capacity.

    I guess that is why you ask the manufacture, they all seem to have different methods.

    I have read the manual but I don't get how the bulk phase can be set at 54v and then the absorb phase at a higher voltage... I assume from what you are saying that the charge controllers will prevent to HIGH a rate during the ABSORB phase? So there is no need to have to shut down anything to reduce array power during the ABSORB phase in order to stay within these limits above?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?
    solarabcd wrote: »
    Yes I was surprised they used the 6hr rate rather than the 20 too but it is 20% of the discharge rate in amps at the 6hr rate, which is 238A x 20%=47.6A).

    This works out at around 2-3% of the full 20hr rate (1808AH). The 275A for bulk charge works out at about 15% of 20hr capacity.

    I guess that is why you ask the manufacture, they all seem to have different methods.

    I have read the manual but I don't get how the bulk phase can be set at 54v and then the absorb phase at a higher voltage... I assume from what you are saying that the charge controllers will prevent to HIGH a rate during the ABSORB phase? So there is no need to have to shut down anything to reduce array power during the ABSORB phase in order to stay within these limits above?

    The BULK mode pushes the most current it can to the battery (with an upper limit) varying as the Voltage comes up until the Voltage reaches the ABSORB set point; there is no specific "BULK Voltage". In ABSORB mode the Voltage is held steady and the current is varied to maintain that Voltage. During BULK the ABSORB timer counts up; whatever time is "on the clock" at the moment ABSORB mode is achieved is the time period the controller will remain in ABSORB (with programmable limits) after which it drops into the lower Voltage FLOAT mode, which it will maintain until this level can't be held due to drop in PV output and/or loads.

    Does that help clarify it? Frankly, the FM80 manual isn't as good as the MX60's (its predecessor) and that was a bit lax in key areas (just my opinion).

    And yes, each battery manufacturer has their own specs for charge rate. I think they do it on purpose - to confuse people!:p
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Thanks Marc.
    What threw me off in all of this was that the battery guy I spoke with indicated that the absorb charge would have to be lower and using either a super-large array or a high output generator to provide the bulk charge, then have something to provide the absorb phase. I assumed the charge controller would take care of the limits if I set them correctly - not sure what he is thinking.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?
    solarabcd wrote: »
    Thanks Marc.
    What threw me off in all of this was that the battery guy I spoke with indicated that the absorb charge would have to be lower and using either a super-large array or a high output generator to provide the bulk charge, then have something to provide the absorb phase. I assumed the charge controller would take care of the limits if I set them correctly - not sure what he is thinking.

    You're welcome.

    One of the advantages, and consequently frustrations, of the OB charge controllers is the amazing amount of programmability in them. There are a lot of options! I found I get the best performance on mine with some changes to the defaults like expanding the maximum ABSORB time to "up to 4 hours" (normally it's 2).

    BTW, one thing they don't tell you (and this is true of any component) is that running them close to their maximum limit (80 output Amps) isn't the most efficient range. The extra heat produced can cost efficiency. Several of us find that 75% capacity seems to be peak efficiency.

    I'll guess what you've got are some industrial batteries, like forklift or telecom units. :D
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Yes I have had a good look at the efficiency levels in the graphs in the manual.

    So to finalize all of this scenario:
    - I set the ABSORB set point to the lower recommended 54v
    - The charge controller will do the regulating after it reaches 54v (or via temp sensing).

    Is it possible then, if I have a massive array and several charge controllers that the current could definitely exceed the 275A during bulk phase? Therefore sizing the amount of charge controllers (and array) so that the most amps hitting the batteries could only be 275A. Do you agree? For example: 275/FM80 at max theoretical amps(80) = 3.4 So 3 of these controllers is the max.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    Actually you can set a charge current limit anywhere up to 80 Amps. 75% of that is 60, so you could have 4 FM80's and set each one's current limit to 68-70 Amps to get your combined 275 Amps. Set the ABSORB Voltage to what the battery manufacturer recommends - usually a '48 Volt' system will ABSORB at around 58 Volts, not 54. Some are set higher yet. Likewise the FLOAT Voltage is usually about 56.

    A note about the RTS - it's very important. For that reason I think having all the FM's connected via HUBb & MATE is a really good idea - as in necessary. That way one RTS will set the temperature variation for all the controllers. One problem you may have is with your type of battery; if it's one of those large, monolith type you can't get a good thermal reading on them. This is a thermal mass characteristic, where the interior temp is different from the outside case. They recommend you attach the RTS to the (+) terminal for that type, but even that may not provide best results.
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Good point. I do actually remember reading that now you point it out.

    The battery guy was adamant that 2.25VPC was the upper limit when charging at 275 amps.

    Actually just to confirm another thought. If I wanted a separate DC genset to to turn on at 50%DOD ,we calculated that the trigger voltage for these specific batteries relative to our current draw (using their charts) was 2.026VPC, so 48.6V.

    I assume if I want the genset to come on as last resort after several days of no sun then whilst there is sun the charge controllers will just do the charging when ever the voltage drops below the ABSORB set-point. After no sun and depletion of the battery to 48.6V, the genset senses this and will fire up and provide charge until its set cut off voltage (which would be 54v based on his guidance if charging at the full 275 amps).
    Am I making sense?
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Also this is where he confused me as he said (and the PDF chart states) the vpc for the ABSORB phase could be 2.3v at a rate of 47.6amps. So that is what raised my initial questions i.e. how can I bulk charge up to his limit of 2.25v and then ABSORB charge at 2.3v.

    The way I understood the charge controller worked is, that it is one or the other not both. Maybe that is why he is thinking you do the bulk charge with one section of the system and have another separate charge controller, wind turbine charger etc working at the 2.3 (55.2v) cut off point at 47.6 amps. What do you think?

    One extra question: Other than using a DC genset, parallel charge controllers from an array or parallel Inverter/chargers like the sunny island, can you recommend other methods to get the charge amps up into that 200Amp range? I am surprised that most inverter/chargers like the sunny island only put out around 100 amps max.

    Any thoughts?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    It's confusing, all right.

    A battery that needs charging is going to have a lower than normal Vpc. You put higher Voltage to it, the Amps flow, the Voltage rises, the Amps taper off. I've never heard of charging at a set Voltage and set Amperage?:confused:

    Maybe he was talking about the cell's resting Voltage being 2.25 Vpc? Or the Float Voltage?

    I don't know how you'd go from charging at one fixed Voltage to another higher one. It doesn't make sense.

    Perhaps the spec he quoted are based on Wattage input: not to exceed 14,850 Watts. I really do not know the answer to this one. Maybe it's not a good battery choice for RE.

    As for the generator question, the auto-start function is programmable to to low Voltage setting. This is done through the Inverter/Charger, and whatever unit you use will have charge input limitations. I can all but guarantee none of them will handle 275 Amps on their own. An Outback VFX3524 will do 85 Amps charging, which is usually more than enough for an off-grid system.

    Maybe we'd better look at your application as a whole.
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Not necessarily a set voltage but up to a set voltage point.

    He is indicating that the batteries can handle that high amperage 'safely' as long as you only take the battery up to 2.25vpc (54v). Then it can handle a reduced rate of 47.6A up to 2.3vpc (55.2v). Or you can just charge at 47.6A all the way to 55.2v if you had no means to charge at the high/fast rate of 275A.

    To me it just makes sense to set the voltage cut off at the recommended 54v and charge as hard/fast as I can up to 275 amp limit and then let the ABSORB phase start from 54V.

    There are a select few large DC gens that put out up to around 245 Amps. To keep RPM and cost lower, around 150Amps seems more practical, pending on the gensets specs.

    Just using an array; it seems like the fastest way to charge is straight from the charge controllers with no inverters in the system. So if the array was big enough and I have 3 x Charge controllers putting out 50amps each then (excluding losses etc) I have 150amps for the batteries. I would need 2 x inverter/chargers to put out around that figure and the cost would be much higher, particularly when I don't necessarily need AC power on site.
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    I should also add that the 47.6A is per string. So if I had 2 x strings of batteries I could charge at 95.2A, so on and so forth. I guess we are talking 'acceptance' rates here, which seem to quite often get left out of the calculations.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    The thing is, the BULK stage has a maximum current setting but there's no Voltage limit; that is set by the ABSORB Voltage. Once that is reached it switches to maintaining that V level. I seriously doubt that the cell Voltage would rise above the limit without the Amperage decreasing at the same time. Not on any system I've ever seen. So it should be safe to go.

    And yes, charge controller's don't need Inverters; they connect directly to the battery. It's just that on some systems they "talk" to each other so there's no disagreement on what's going on, so to speak.

    But you'll need a huge array for that kind of current:

    275 Amps @ 54 Volts = 14,850 less losses = 18,500 Watts total (and four controllers set to max to handle it probably).
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Yes I agree it would be a massive array and not practical, hence the use of a High amp output DC genset. But I needed to do the sums for comparison.

    If the voltage set point is lower at 54v, then would this just mean that the ABSORB would take longer to complete. So effectively it just means the bulk charge fills slightly less of the battery than if it was at say, 56v before it cuts off.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?

    Heck, you'd only need like 100 Evergreen 200W panels @ $640 each .... plus wiring, mounting, fuses, taxes ....
    :cry:
  • solarabcdsolarabcd Solar Expert Posts: 38
    Re: Disconnecting charge controller after bulk phase?

    Out of curiosity Marc, what does the output of your controller change down to once the BULK stage is finished?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Disconnecting charge controller after bulk phase?
    solarabcd wrote: »
    Out of curiosity Marc, what does the output of your controller change down to once the BULK stage is finished?

    It is impossible to say, as my system remains active during charging. As such, any current flowing into the batteries during ABSORB includes compensating for any loads that might be running at the time. The inverter itself draws current even when idle.
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