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 > Automatic, smart battery charger?

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full_mosey

Oklahoma

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Joined: 01/16/2011

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Posted: 02/04/18 09:47pm Link  |  Quote  |  Print  |  Notify Moderator

Here is the Amps graph for today 4 Feb:

Amps:
[image]

What is interesting/alarming to me is that the Amps went lower and never leveled out as I expected. Abs lasted nearly 6hrs, somewhat less than 2Feb. The late afternoon switch to Bulk=5 is due to waning V-array. The controller is trying to hold the V-batt to Target Volts.

Where is the bottom? Was the bank badly sulphated?

I will keep Float cancelled and wait and watch for a leveling out.

Maybe the race to Float is a fool's errand!

HTH;
John

full_mosey

Oklahoma

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Posted: 02/07/18 12:01pm Link  |  Quote  |  Print  |  Notify Moderator

I am working with the definition of a topped-off battery is "...when a low point of Amps is reached and held for 15 minutes during Abs.". I became weary while waiting for days to see the charge Amps flatten out at a low Amps. Weather was not cooperating.

Last night I used garage/shore power to run the 50A Magnum inverter/charger. I wanted the next day to begin with a fully floated bank.

[image]

It is a clear sunny day. In this graph you see the Magnum maintaining 14V Float Voltage until sunrise. Did I say I use temp-comp chargers? I ran the Magnum from 4PM to 8AM. By 9 the MPPT was holding the V-batt at 15V and Amps were steady at ~1.68A. The Target Volts smothers the V-batt.

This exceeds the top-off rule of thumb, and we are ready for the MPPT to Float.

Parasitic draws are:
Magnum on standby
2 x Dometic 12V CF-35 fridges
12V to USB adapter
Raspberry Pi 3 B

HTH;
John

full_mosey

Oklahoma

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Posted: 02/20/18 10:08am Link  |  Quote  |  Print  |  Notify Moderator

Why is an adjustable, temperature compensating charger important? We all should know that a battery at 25C is usually charged at 14.4V. We know we can set most chargers to 14.4V But, how often is your battery actually at 25C? Plus how often is 14.4V the correct charging Volts? The answers to both are "Not often".

[image]


This is a graph of the bank in my van covering ~260 days. It includes the extremes of Summer and Winter.

The V_Target is the regulated Absorption Voltage as calculated based on the battery temperature. I capped this at 15V.

The plots are of the first minute of the day when the Morningstar SS MPPT 15L wakes up and switches from night to Bulk stage. These are the starting bank temps and charge Volts. Normally the bank temp rises and Volts are reduced during the day. The 15L automatically monitors temps and adjusts Volts throughout the day. Even Float volts are regulated by battery temperature.

Summer is not too bad.

In Winter the constant 14.4V is way too low. With a constant 14.2, 14.4, 14.6, 14.8 setting type of charger, it never is right most of the time. Some chargers have an extra-time override, but then again, it may still not be enough Volts to top-off/finish the charge.

Comments?

HTH;
John

full_mosey

Oklahoma

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Posted: 02/24/18 08:56am Link  |  Quote  |  Print  |  Notify Moderator

Here are an interesting two graphs that show a difference between parallel and series connected 12V panels with MPPT. I have a TT and a van in the driveway. Both have their own panel arrays and they have been subjected to the same weather.

This morning, I was greeted with the fifth consecutive day of inclement weather. It was dense fog followed by rain and then complete overcast. We had freezing rain for 3 days beforehand and the panels were covered with ice until yesterday with about half covered overnight.

First, the series graph of the van.
[image]

You see V-Array, or solar Volts, beginning at 13V and the controller in Bulk. Next V-Array rises until the sky darkens and the rain begins where the V-Array drops back to 13V. After the rain passes, the V-Array rises to 32V where we see some more Amps.

Second, the parallel graph of the TT.

[image]

Here you see what happens when the V-Array Volts are cut in half due to the parallel setup. Charging starts out as above, but when the rain began the V-Array dropped low enough that the controller went into NIGHT/DISCONNECTED mode. Once the V-Array rose back to 13V the controller reverted to Bulk mode.

Comments?

HTH;
John

pianotuna

Regina, SK, Canada

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Posted: 02/24/18 09:14am Link  |  Quote  |  Print  |  Notify Moderator

Hi John,

Thanks for providing data that demonstrates what I've suspected for years--that higher voltage panels deal with poor solar harvest conditions better than lower voltage nominally 12 volt panels in parallel.

My own system input voltage to the controller is 33. I get some charging even in rain.


Regards, Don
My ride is 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.

full_mosey

Oklahoma

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Posted: 02/24/18 05:47pm Link  |  Quote  |  Print  |  Notify Moderator

I will be rewiring the parallel array to series.

HTH;
John

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