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Open Roads Forum  >  Tech Issues

 > question on interpreting MPPT controller display

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3 tons

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Posted: 09/03/17 03:23pm Link  |  Quote  |  Print  |  Notify Moderator

Short answer, yes amps drop off as battery nears full due to increased internal resistance (like pumping up an inner-tube...), particularly when approaching 90% state of charge (SOC) and above...

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BFL13

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Posted: 09/03/17 03:55pm Link  |  Quote  |  Print  |  Notify Moderator

"
I thought the controller always showed the max potential harvest, when evidently, it is only displaying the usable amps based on the needs of the batteries"

Not if there is a load too. Then it (at the controller) will show the total demanded amps up to the limit of the output supply at the time.

I used to think my Trimetric showed "net amps" but was corrected on here by somebody who knows better. The Tri shows only the amps in or out of the battery. The math works as though it is net, but it isn't. You need two ammeters and then can derive it all.

How does the wiring for your "battery meter" (Magnum monitor) get to show the amps to the battery from the solar controller? AFAIK you need a shunt somewhere there. Interesting. I do wonder if you are seeing what you think you are seeing, but you know the set-up and I don't.

In the OP you mention that the amps are coming from the panels. Actually with MPPT controllers (which have buck converters) it is not really like that. You get input watts to the controller, then output watts, and only now can you take your amps from those output watts.

The input amps depends on the input watts divided by whatever voltage the MPPT controller is running itself at. Not much related to output amps because of the buck converter. With ordinary PWM controllers, there is more of a direct relationship between amps from the panel and controller output amps.


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pianotuna

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Posted: 09/03/17 08:02pm Link  |  Quote  |  Print  |  Notify Moderator

Hi,

I hate to say this but the BZ controllers are not good. In fact in a head to head test with a PwC the PWC outperformed the BZ MPPT.

outwestbound wrote:

pianotuna wrote:

outboundwest,

It may depend on what is selected for set points. What controller do you have? Have you changed the stock settings?


the set points are per my batt manufacturer. I used some simple MPPT controllers made by BZ Products in the US. I don't have displays inside my camper. My Magnum 3012 display, because it has the batt monitor, gives me a net amp figure. This net figure is the gross on the controller, less the load (devices + phantom), which is fine for me. I wanted simplicity.

Someone answered my question I think. If I'm under good sun and if in BULK, harvesting 55 amps, but then in FLOAT, the controllers show only 25 amps, in the same sun, then that answers my question.

I thought the controller always showed the max potential harvest, when evidently, it is only displaying the usable amps based on the needs of the batteries.



Regards, Don
Full Time in a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

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Posted: 09/03/17 08:17pm Link  |  Quote  |  Print  |  Notify Moderator

CCs generally show the output amps. BUT the output amps supply the house load and the battery charging. It only reflects battery amps/charging when the house loads are small or 0A.

My controller can also display the panel A, V and W. The input power will be the same as the output power after adjusting for CC efficiency losses. In other words the CC adjusts the needed panel power to match the output power.

* This post was edited 09/03/17 08:24pm by CA Traveler *


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Posted: 09/03/17 11:16pm Link  |  Quote  |  Print  |  Notify Moderator

charge controller shows what the charge output is at that moment
might show 15amps, but if you have vent fans on, etc.. charge into batteries might be 10amps

the controller can show MAX if MAX is being used
it can NOT show what might be available while sitting in full overhead SUN
ONLY what is being output,


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Posted: 09/04/17 01:51pm Link  |  Quote  |  Print  |  Notify Moderator

[quote=BFL13]

How does the wiring for your "battery meter" (Magnum monitor) get to show the amps to the battery from the solar controller? AFAIK you need a shunt somewhere there.

Quote:



The ME-BMK has a shunt which measures current going into or out of the battery, as I understand it. Magnum offers these for about $165 and they just work with their inverter/chargers and give you the display through the panel you already get with the inverter.


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outwestbound

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Posted: 09/04/17 01:53pm Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Hi,

I hate to say this but the BZ controllers are not good. In fact in a head to head test with a PwC the PWC outperformed the BZ MPPT.

outwestbound wrote:

pianotuna wrote:

outboundwest,

It may depend on what is selected for set points. What controller do you have? Have you changed the stock settings?


the set points are per my batt manufacturer. I used some simple MPPT controllers made by BZ Products in the US. I don't have displays inside my camper. My Magnum 3012 display, because it has the batt monitor, gives me a net amp figure. This net figure is the gross on the controller, less the load (devices + phantom), which is fine for me. I wanted simplicity.

Someone answered my question I think. If I'm under good sun and if in BULK, harvesting 55 amps, but then in FLOAT, the controllers show only 25 amps, in the same sun, then that answers my question.

I thought the controller always showed the max potential harvest, when evidently, it is only displaying the usable amps based on the needs of the batteries.


I specified Morningstar and forgot to order them before arriving at the solar place. The fellow had been using these for 20 years, so I tossed them in. They were making about the PV panel labels.

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Posted: 09/04/17 01:56pm Link  |  Quote  |  Print  |  Notify Moderator

MrWizard wrote:

charge controller shows what the charge output is at that moment
might show 15amps, but if you have vent fans on, etc.. charge into batteries might be 10amps

the controller can show MAX if MAX is being used
it can NOT show what might be available while sitting in full overhead SUN
ONLY what is being output,


Thanks

outwestbound

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Posted: 09/04/17 02:02pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks everyone for your comments.

BFL13

Victoria, BC

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Posted: 09/04/17 03:09pm Link  |  Quote  |  Print  |  Notify Moderator

outwestbound wrote:

BFL13 wrote:



How does the wiring for your "battery meter" (Magnum monitor) get to show the amps to the battery from the solar controller? AFAIK you need a shunt somewhere there.

Quote:



The ME-BMK has a shunt which measures current going into or out of the battery, as I understand it. Magnum offers these for about $165 and they just work with their inverter/chargers and give you the display through the panel you already get with the inverter.


Interesting! There are several folks on here with that sort of inverter/charger who might not know they could maybe do that with theirs.

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