Charge stages on a simple marine system

[Nvert]

I have two new AGM batteries powered by two small panels wired to a new Xantrex 35C controller. It appears to be maintaining the batteries, despite generally wet cloudy weather since installation, but the batteries never get above 12.5 even in rare sunny periods. Seems like I should see bulk charge rates (up to 14) when the sun comes out, and a float level (13+) when batteries have not been drawn down.
I used small Nature Power controllers in previous configuration with lead acid batteries, and they regularly showed what seemed like normal bulk and float rates when it was sunny. The NP controllers never lasted much longer than a year though, before apparently succumbing to marine environment.
Why am I not seeing normal charge levels? No luck reaching Xantrex tech support.

( I’m a new member here. Happy to find you guys. Best of luck in ‘24.)

 

[Rocketman]

Check the settings-

if you continue to have issues- look at a Victron mppt 100/20 (or whatever is the correct size for your panels). Victron made its name in the Marine industry.

 

[wholybee]

You are torturing your batteries and are going to kill them.
The reason you never see 14V is because even in sun your 2 panels are not able to put out enough current to get the battery voltage that high. The voltage will rise as the batteries charge, but unless you are able to put out a lot of current (30-40 Amps, probably) you will not see 14V until the battery is nearly fully charged. In the past, if you had flooded batteries, only one instead of two, or if they were nearly fully charged, would explain why you saw 14V then, but not now.

The batteries are low, and failure to get them fully charged daily (or at least most days) will result in the batteries having a short life. It is very difficult to do that with solar, unless you have a lot of it. I don't know how much "two small panels" means, but for 2 AGM batteries of about 100Ah each, I would expect you need 400W of solar to charge them properly. To charge them on cloudy days, or if you have higher daily power usage, you might need even more.

I second the recommendation for a Victron Smart controller. They are very customizable and provide good information about what the panels and battery are doing. And MPPT will also work slightly better than a PWM. Also, the Victron BMV-712, so you know how much power you use daily, and if the batteries are getting a full charge.

 

[mikefitz]

The 35C controller is a PWM type so will never extract full power from the panels. The 35C is not easy to set up and is not the ideal controler for a solar set up, good for hydro or wind power.
The charge voltage setting is by potentiometers , what volts have you used?

Without details of battery model, a useful setting would be 14.6 volts bulk charge and 13.7 volts float.

If its not too late return the Xantrex and consider a Victron Smart Solar controller.

It may be worth testing the panel output for volts and current, there are you tube guides on this.

 

[Nvert]

Thanks very much for your replies and advice. I did set the potentiometers at the suggested settings for AGMs, which I believe is what is shown above (I'm away from the boat at present). Probably W and R are correct in asserting I need a different setup, like the Victron.
My two panels are Nature Power 15w, supposedly capable of 847mA in bright sun. I've had them for 5-6 years, but almost always with the two lead acid batteries and the little NP charge controllers (130w/8A). Never needed shore power; made trips up and down CA coast. Don't ask why I changed, but I take it all that is different now with the AGM, so I will look into the suggested Victron. Again many thanks for your replies.

 

[time2roll]

Need to get those batteries charged as they are sulfating. More solar or a portable charger on utility power asap.

For the effort get a 100 watt panel as a minimum.

 

[Rocketman]

With only 30w a Victron mppt 75/15 will be sufficient- but you really need more than 30w of solar. Do you have the room to put a 100w panel up? Or two 100w panels? If you do remove the 15w panels or keep them as is. Do not connect them with the newer panels.

The mppt 75/15 can output 220w of power - so it will be fine whichever way you go.

A 100w solar panel on Amazon is $60 to $80.

Good Luck

 

[mikefitz]

two panels are Nature Power 15w

These most likely have lost the will to live. Flexible panels degrade, reduce output and often fail after a few years. I suspect this is where your problem lies. Even if fully operational, 30 watts seems too small.
You don't specify the AGM battery capacity, or the application, so suggesting required panels or controler is difficult.

 

[wholybee]

30W will on average, on a sunny day, produce 10Ah per day. Your 2 AGM batteries are probably about 100Ah each. So, on a sunny day, you can only charge your batteries by about 5%. My 400W recommendation above is based on you using 50% of the battery per day, plus a bit reserve. To really know how much solar you need, you need to calculate your actual usage.

 

[Marinepower]

AGMs are more fussy to charge then lead acid and more prone to sulfation if not fully charged on a regular basis. They are better in many ways (charge acceptance / deep discharge) but harder to keep happy.


You really should have a minimum of 10% of the combined amp hour capacity of your AGM bank in a shore charger. I would say 3-4 times that amount in solar, to take into account cloudy days / winter sun.

Also, is your Xantrex temprature compensated? If not, you will need to add around ) 0.1 votls bulk/absorb for each 5 degree celcius below 25c.

 

[Nvert]

Thanks again guys. Really appreciate your comments and advice.
My boat is a 33’ J100, a racer and day sailer. I sail her once a week. Loads are pretty minimal.
I use these little panels because I could mount them on the stern, where they are always in the sun.
I will get my charger on the batts (but there really haven’t been any loads, so hopefully my current setup has acted as a trickle charge) and when I get back there I’ll test those panels again (showed solid charge when I connected the Xantrex) and replace if needed. Also ordering the 75/10 Victron. Could also use my old rod holder solar charger that connects to the 12v plug, for a little extra charge, which also worked great for couple years until I got tired of shlepping it in and out of lazarette.