question on interpreting MPPT controller display

[outwestbound]

Hi. This is intended to be general. If an answer can't be made without knowing the exact unit, then please let me know. My question may be poorly phrased.

Does the amount of amps shown on the controller as coming in from the panels depend on the battery bank's state of charge?

I have an 830AH AGM batt bank and 960 watts of PV panels. When I originally tested the system, the bank was DOWN 250 AHs and the controller was bringing in about 55 amps from the panels in BULK mode. Now, I'm only DOWN about 65 AHs, and in similar sun conditions, the controllers are indicating only about 24 AHs in FLOAT mode.

Does the controller always show what the max coming in can be, or does it show what the battery bank is capable of accepting, depending on the banks state of charge and thus, the mode the controller operates in (e.g., bulk, absorption or float).

Hope this makes sense.

[pianotuna]

Hi outwestbound,

To adjust the Magnum charging rate, touch favs, then rotate the dial until F3 appears. That allows you to select the number of amps that the Magnum will draw from shore power (lowest setting is a mere 5 amps) or from a generator (in my case 24 amps from the Yamaha 2800 sIEB).

I do use this feature to limit my demand to 80% (12 amps for a 15 amp, 24 for 30, and 40 for a 50 amp shore power).

If you are in load support mode this will trigger it sooner. If there is poor voltage then limiting the amps can "force" the Magnum to do voltage support and not just load support. I DO NOT RECOMMEND THIS.

Voltage support is best done with an autoformer.

[pianotuna]

Hi outwestbound,

Another thing that happens with the starved acid AGM design is that the cells literally can not get to 100% discharge--they can't because they run out of acid before the plates run out of active material. If there were a way to add more acid they could be discharged more.

My own personal view is that the lack of acid works to protect the plates and may slow down the shaling that always occurs on the positive plates.

That is, I think, also why a 100 lb flooded jar will have slightly more amp-hour capacity than an AGM of exactly the same weight.

The surplus acid format that I use does not offer that protection--so I need to be careful to not take the jars down below 50% state of charge.

[pianotuna]

Hi red31,

Slight over charge is fine with a flooded jar, because if it gasses you can top up the electrolyte with distilled water.

You can not "top up" an AGM so I'd always attempt to keep the voltage slightly below the gassing numbers. I.E. do not overcharge an AGM unless you intend to equalize it.

red31 wrote:
is that @ 14.0v or 14.7v? , '14.7'

I'd rather dance on the side of slight overcharge than constant undercharge.

[pianotuna]

Hi outwestbound,

Equalization on a flooded jar is done by exceeding the gassing voltage. If it is done while connected to the RV the top limit for voltage is 15.4. Higher than that, and there is a risk of frying the computer boards in the fridge and other (expensive) items.

If the bank is disconnected, then equalization voltage may go up to 16 or 17 volts. You WANT the jars to gas. Distilled water can be added to flooded jars to make up the losses.

On an AGM, if it gasses beyond the valve regulated pressure, the cells will vent--and there is no way to replace the lost electrolyte. That means permanent lost capacity.

BFL13, MrWizard. and I are all using a special subset of AGM called "surplus acid". They are used in telcom cell towers. They are closer to flooded and are GREAT for low long draws. Your full river jars require different charging protocols, because they are a "starved acid" design. I'd advise you to follow their charging recommendations "to the letter", if you want long life. Standard AGM jars require fairly high charging rates to "wake them up", and they accept more current than regular flooded jars.

Flooded jars start to taper on charging at 85% SOC.

outwestbound wrote:


I have no knowledge in this particular area, but why would the sealed battery profile have no equalization? This poses no risk if they get equalized every 29 days in the flooded profile?

I decided to stay 12Vdc on the bank. Too much brain damage to change!

[outwestbound]

checked settings. max charge set at 80%, so that's good. the indication of full is set to display "float charging". set points on the charger appear to match batt specs.

it's floating at 3amps going in, so looks full!

thanks for indulging the creep in this post. I'll read up on this stuff and write up a diagram and spec sheet on what I have. then I'll pay a consultant this winter to help me answer whether a better controller and/or generator setup will make sense. I'll also know more after using the stuff a couple more months.

you all have been very helpful. thanks so much

[BFL13]

Here are the exact charging instructions for those DC 400-6s

http://resources.fullriverbattery.com/fullriver-battery/charging-instructions/batteries.pdf

Note the way they mark end of the absorption stage, and when it is full. You need the meters and set up to be able to see when you are there.

Note they suggest (it is not a law) to use 20% charging rate as a way to save gen time. You can go higher but not much. My AGMs say 27% max.

20% of 830 is 166 amps. Your charger goes to 125 amps. But your Honda 2000 can't do that much in VA even with the power-factor correction in the charger.

You can do it on shore power at the lower rate since time does not matter, but off-grid using the Honda you will have to dial down the amps of the charger like PT does so the Honda can do it or else get a second Honda to parallel them. However, if there is sunshine you can charge with the Magnum and solar at the same time and they will add their amps, so that would help.

Having so much battery is causing an imbalance in your set-up. Looks like you will need some generator /Magnum time (with solar on too) to do your Bulk, and solar to do the rest if you expect to reach Full in daytime while also running the RV.

You might want to set up for split- bank operation since you have so much battery. Run the rig on one set of 415 and get the other set to proper full. Then swap around.

[outwestbound]

pianotuna wrote:
Hi BFL13,

Equalization should only be done on AGM jars when loss of capacity is noticed. It needs to be done gingerly while monitoring temperatures and amperage draw. Charge voltage must be close to the gassing voltage (which is temperature dependent) but should NEVER exceed the gassing voltage. This has the quaint name of "dancing on the needles".

this equalization process is what concerns me about setting the BZ controllers to flooded, cuz it seems to say that it will equalize every 29 days @ 14.9Vdc. I'll call BZ and see if I can set equalization on manual for the flooded profile, if this makes sense.

[outwestbound]

BFL13 wrote:
Don't forget you have to add more AH in than went out just to stay even. Charging efficiency. That varies over the SOC range. On my Trimetric monitor I find I need to go to about 15AH "over" to get to the point where the batts (about 430AH worth of open flooded) are full by hydrometer count.

The Tri has an adjustment for that if you fiddle with it and every day were the same. (they aren't of course) I don't bother. If it gets to about + 15AH and solar is done for the day, I reset the Tri AH to zero. (on solar don't leave the Tri in auto-reset!) If it doesn't get that high, as is often the case on partly cloudy days, I don't reset the Tri. Only reset when you know your batts are full---not when the bogus Tri instructions say "full" is.

I'm beginning to appreciate using only the amps and volts figures and not these SOC percentage and other indicators shown on the inverter/charge display.

My charger is doing exactly what you say; very helpful. I started the Honda at -45 and the amps are at about 10ish and I/O is +6, so thanks for the info. I couldn't have forgotten it, because I never knew this 🙂

[outwestbound]

pianotuna wrote:
outboundwest,

The Magnum running flat out at 125 amps of charging only draws 15 amps. I think that was pretty clever of them--because it means you can charge at full bore on a 15 amp shore power supply.

In real life, I limit mine to 12 amps, because I don't believe in drawing more than 80% for long periods of time. This also limits my charging amps to the maximum my bank can safely accept.

On your bank, fully charged would be when the rate reaches between 8 and 9 amps.

Very helpful. Thanks. In early 2016, Lifeline ran themselves completely out of inventory on the L16 6v. Couldn't get then anywhere in Florida, so I punted and got Fullriver DC 400-6, which offered the same form factor. The bank's location had already been built and planned for, so size was important.

You've been very gracious with your time as this thread has crept from my initial question. I need to do my homework and re-read the literature and get converse in this again. I'm going off my memory from a year ago, and haven't thought about this since.

Because I'm comfortable with math, I recall wanting to run the figures in an excel spreadsheet from PV panel through the system, but there are so many efficiency factors that I recall it was frustrating.

My phantom load is about 2vdc, so I'm assuming if my magnum panel is telling me 6-7 amps charge rate at the end of the process, then that's about 8-9 at the battery, using information I've learned in this thread. Yes, the loads obscure the measurement of voltage - frustrating.

To limit the charger's power input from shore down from 15 to 12, are you just using the shore setting and turning it down?

[BFL13]

Don't forget you have to add more AH in than went out just to stay even. Charging efficiency. That varies over the SOC range. On my Trimetric monitor I find I need to go to about 15AH "over" to get to the point where the batts (about 430AH worth of open flooded) are full by hydrometer count.

The Tri has an adjustment for that if you fiddle with it and every day were the same. (they aren't of course) I don't bother. If it gets to about + 15AH and solar is done for the day, I reset the Tri AH to zero. (on solar don't leave the Tri in auto-reset!) If it doesn't get that high, as is often the case on partly cloudy days, I don't reset the Tri. Only reset when you know your batts are full---not when the bogus Tri instructions say "full" is.

[red31]

pianotuna wrote:

The bank is AGM and they start to taper at about 95% state of charge. The bank is 830 amps so the last 5% is about 41.5 amps. He gets 55 less the 7.3.

is that @ 14.0v or 14.7v? , '14.7'

I'd rather dance on the side of slight overcharge than constant undercharge.

[outwestbound]

pianotuna wrote:
outboundwest,

The Magnum running flat out at 125 amps of charging only draws 15 amps. I think that was pretty clever of them--because it means you can charge at full bore on a 15 amp shore power supply.

In real life, I limit mine to 12 amps, because I don't believe in drawing more than 80% for long periods of time. This also limits my charging amps to the maximum my bank can safely accept.

On your bank, fully charged would be when the rate reaches between 8 and 9 amps.

Thanks. I was -45AH and started the Honda a little while ago. The SOC now says 100% and the -45 deficit is now a positive number, but the charge remains in absorption and is down to about 11 dc amps. It flashes like 7 or 8, but stabilizes around 11. From what I hear above, I should let it get to "float", which should be around 8 to 9 amps. If this is correct, I may have been shutting off the Honda too soon, as I was looking at the other indicators above on the display.

[pianotuna]

Hi BFL13,

You forgot to mention positive plate shedding which happens with every cycle and there is not a darn thing anyone can do about it.

You can more or less eliminate sulfation of the negative plates--you have proved this for literally years, and have documentation to prove it. (ty again for all your efforts).

In the OP's case fully charged may be between 8 and 9 amps.

You do need an ammeter and a volt meter.

Equalization should only be done on AGM jars when loss of capacity is noticed. It needs to be done gingerly while monitoring temperatures and amperage draw. Charge voltage must be close to the gassing voltage (which is temperature dependent) but should NEVER exceed the gassing voltage. This has the quaint name of "dancing on the needles".

BFL13 wrote:

Slow death by gradual sulfation is the fate of every battery, but you can speed that up by leaving them less than fully charged. It is only "damage" if it happens too soon for your battery budget. How much effort you put into caring for the batts is situational to your circumstances and the scenario.

The ONLY way to know if an AGM is truly full on a recharge is to observe the amps it accepts at the end of the recharge while the battery has no load on it.

You must have an ammeter and a voltmeter.

The regularly scheduled "equalization" on some chargers' profiles like once a week or once a month is not really a desulfation level equalization at all. It is just a dose of the regular "bulk" voltage of 14.x to prevent stratification of a flooded battery. N/A to AGMs AFAIK.

You have serious long drawn out tapering of the amps between 95-100% recharge so getting to proper full is not easy. Especially when the usual blurbs say "full" is when amps get down to about 2% of bank capacity in AH. That is maybe 98% SOC depending. So they are inviting you to be sulfated sooner than you might like.

[pianotuna]

outboundwest,

The Magnum running flat out at 125 amps of charging only draws 15 amps. I think that was pretty clever of them--because it means you can charge at full bore on a 15 amp shore power supply.

In real life, I limit mine to 12 amps, because I don't believe in drawing more than 80% for long periods of time. This also limits my charging amps to the maximum my bank can safely accept.

On your bank, fully charged would be when the rate reaches between 8 and 9 amps.

[BFL13]

"My batts are (4) 6v, 415AH bats serial/parallel for 830AH @ 12Vdc. Do you know how often they should be brought to full charge in order NOT do damage them? "

Slow death by gradual sulfation is the fate of every battery, but you can speed that up by leaving them less than fully charged. It is only "damage" if it happens too soon for your battery budget. How much effort you put into caring for the batts is situational to your circumstances and the scenario.

What is the battery model/brand exactly? It would help to see the spec sheet for them.

I thought they were flooded, but PT says they are AGM. AGMs need occasional "reconditioning" if left undercharged at times. Equalization of a flooded battery is ok because the gasses go off, and you can water them, but a sealed battery can't do that (unless it vents--oops)

The ONLY way to know if an AGM is truly full on a recharge is to observe the amps it accepts at the end of the recharge while the battery has no load on it.

You must have an ammeter and a voltmeter. This is hard to achieve while RVing when there is a load on the batts. (With open flooded, you can use an hydrometer--wear the same shirt and pants until the holes get too big and then start over with the next set of "battery clothes" )

The regularly scheduled "equalization" on some chargers' profiles like once a week or once a month is not really a desulfation level equalization at all. It is just a dose of the regular "bulk" voltage of 14.x to prevent stratification of a flooded battery. N/A to AGMs AFAIK.

No idea of your scenario etc, but I can say I learned to carry four batteries in summer while on solar instead of the six I use in winter with no solar. ISTR, 2oldman on here, also reduced his battery bank size which was too big for the solar to get done in a normal nice day.

You have serious long drawn out tapering of the amps between 95-100% recharge so getting to proper full is not easy. Especially when the usual blurbs say "full" is when amps get down to about 2% of bank capacity in AH. That is maybe 98% SOC depending. So they are inviting you to be sulfated sooner than you might like.