Battery Charge Requirements

BFL13 X3

To make life easier, you can use a twist timer as MEXICOWANDERER suggests.

I have 120 watts fixed on roof through controller; with good sun, that's all we need. I have a 100 watt portable panel that I connect directly to batteries when needed.

My $15 e-bay POS PWM controller has no problem just being bypassed.

Regards,
Doug

Just remember, unless you want to become a PLATINUM GRADE BATTERY SHOP CUSTOMER...

Charge those batteries long enough to allow a few of the cells (meaning all) to bubble 1 or 3 bubbles per second per cell PER WEEK. Meaning once a week. I like to do it twice a week but then I hate buying batteries. Nothing on the face of the earth can substitute looking in a cell and verifying the electrolyte is starting to bubble. By doing this, and then looking at the voltmeter and ammeter and CALIBRATING what happens when, you can eliminate the visual check after a few trial runs.

It is Damned tough to beat an INTERMATIC spring wound 2-hour timer to bypass and over-ride the solar controller. But you have to start with the batteries almost charged and 2 hours of good daylight left. Wind up the timer and let it have at it. Don't let the voltage creep past 15 volts doing this. When you are ready to equalize, shut off the coach power switch and wind up the timer two or three times after the batteries have charged as much as they can.

A hydrometer, that is a real one, not a toy, works excellent to verify battery charge. It is the supreme court of verifying state of charge in a battery. I recommend a FRANCIS FREAS. BUT BUT BUT, by doing the timer battery bubbling twice a week or at least once a week you will reduce the need for using a hydrometer by 80% and the need for equalizing 90%.

NOW, you MPPT and PWM Freaks, out there, will BYPASSING the controller BUT NOT ISOLATING IT damage the controller?

pianotuna wrote:
Hi,

12 volt panels are nominally 17 volts. PWM controllers operate at the battery voltage.

Pianotuna, I don't understand the 2nd part of this response, please elaborate. Looked like you set the controller for the type of battery which then uses the applicable settings. On some you can choose custom setting and set them to whatever you want up to the units max.


I am planning on just one panel to start and will see how it works out, we're not heavy consumers so hopefully one is enough. One panel that fits (narrow), would be either 100 or 130w's. Still have to measure for length.

Most any controller with a float voltage will charge and maintain those batteries just fine.

Hi,

With the number of watts planned for there is no need to by pass the controller.

X2 BFL

Padlin wrote:
Looking into a solar setup for my new trailer, first off is figuring out what I need for controller output to correctly charge my batteries. I'm planning on eventually having a pair of either 100w or 130w panels, that's all the space I have.

Batteries are 2 6v Interstate GC2-XHD, 232Ah.
Specs show per 6v
Bulk 7.2v
Absorption 7.75v
Float 6.6v
Equalization 7.8v

Do I read this right I need a 12v controller that will put out double these figures? Very few do, and those are user configurable to get to those levels (Blue Sky Solar Boost 3000i MPPT or Sun Chaser PWM, among a couple others).

My pair of GC2-XHDs are quite happy with a single 130w panel and a Solar30 PWM controller. The controller is set to 14.8v for daily operation. You could use a second 130w panel in the winter when demand is higher and solar day is shorter.

Expected max amps with a 130w panel is 8.2a (panel Isc) and you might see a few more amps at times so use a 15a controller for one panel or a 30a for a pair. Roof mounted flat you might get 50-60AH day from one on a really good day, so your daily usage determines if you need the second panel. IMO try it with one panel and a 30a controller (in case you get a second panel)

You only need to go into the 15s for voltage once in a while for your 100% SOC "overcharge" and with solar you don't need to have a fancy controller that can be set that high, you can just disconnect/by-pass the controller and go "panel direct" That is the same drill as doing an equalization with a manual charger--you have to be there and make sure voltage does not climb too high, take your SGs to see when SG stops rising and you are done. Also disconnect batts from rig to not let the fridge DC voltage go over its 15.4v limit.

Then go back to normal operation with the controller in the mix.

Hi,

12 volt panels are nominally 17 volts. PWM controllers operate at the battery voltage.