Renogy Wanderer 10A LiFePo4 "excess production"

[ctrout]

I have been running a few panels on my RV (3x 100w Renogy mono, 40A MPPT, 3x 110AH AGM) for several years and not really thinking about it but recently decided to build a more "well planned" system for my sailboat. I bought an Amperetime 200AH battery and a Renogy Wanderer 10A controller to charge it with. In testing this new system out at home, I have found that when the battery is full, the Wanderer begins pulsing 41v at 0.4A with two, 100w panels in series. I disconnected one panel but it still pulses about 20v at 0.4A. A minor annoyance is that this causes my cheap 750w inverter to cut out and alarm for overvoltage. My bigger convern is that the battery is supposed to charge at no more than 14.6v. If I install this system in my boat, am I going to be damaging my battery by hitting it with 20v @0.4A all week while it sits in the marina between trips? Is it normal for a PWM to do this? I was reading the thread " What happens with excess production off grid?" (https://diysolarforum.com/threads/what-happens-with-excess-production-off-grid.29040/) And it seems that the understanding is that the panel should go to Voc @ 0.0A when the battery is full. Mine goes to Voc @0.4A.

As an aside, I have ordered a 40A MPPT and 2000w pure sine inverter to use with this battery at home while the boat is in storage over the off seasons but was planning on using the 10A wanderer and only one 100w panel on the boat. It's a Catalina 22 so not much room for a ton of panels.

 

[DJSmiley]

Pulsing is exactly the behavior of a PWM controller: Pulse Width Modulation.

For a PWM controller, to gain maximum efficiency, it's recommended to have the panel voltage as close to the cell voltage. This is also the reason why there are '12V' or '24V' solar panels on the market. They do give a higher voltage (16-20V for a 12V panel) which is exactly what suits a PWM controller.

Basicly, this is legacy solar charging, how they used to do it. It does work fine for lead acid, those don't mind the short bursts and they have a self discharge so in the end everything is fine.
A PWM works by either connecting the panelvoltage directly to the battery (using the panel's current limit to reduce the voltage), and disconnecting, where the connect/disconnect time varies depending on SOC.

A higher panel voltage is basicly unused, it only causes, as you see, higher spikes. The PWM can't efficiently use the higher voltages since it doesn't regulate voltage, it regulates bursts. The higher the input voltage, the less efficient the controller is.

They also usually can't handle high PV voltages (since that doesn't make sense). Your Wanderer ( assuming its https://www.renogy.com/wanderer-li-30a-pwm-charge-controller/ ) can handle up to 25V. If you've connected 2 panels in series (40V) you probably have fried the controller...

Nowadays, MPPT controllers aren't expensive anymore so there is no reason to stick with legacy old PWM controllers.
Higher panel voltages are switched down (step-down) to battery voltage with high efficiency. And a higher voltage allows thinner wires, and less voltage drop in the wiring.
Also, it's not connecting panel voltage directly to the cells (causing short bursts unlike a PWM), thus in the end its much better for LFP.

Anyway: Wait for the MPPT, put panels in series and enjoy.
The Renogy? Probably fried (25V max PV input, you've applied 40V). If not fried, sell it to someone who likes 1998's techniques of solar and leadacid.


Nice example of a PWM:

 

[ctrout]

Thanks for the quick reply. The little 10A PWM seems to have handled the 40v just fine. I have it down to just one panel today and it was charging nicely. It actually threw an overvoltage code when I tried to install a third panel in series, so the overvoltage protection to the controller works. My concerns over the 20v pulsing has me thinking that I really don't want to use the PWM on my LiFePo4. I guess I'll be ordering a small MPPT for that purpose.

 

[MisterSandals]

I guess I'll be ordering a small MPPT for that purpose.

Here is a great little MPPT: (Victron 75/15)

Amazon.com: Victron Energy SmartSolar MPPT 75V 15 amp 12/24-Volt Solar Charge Controller (Bluetooth): Industrial & Scientific

Buy Victron Energy SmartSolar MPPT 75V 15 amp 12/24-Volt Solar Charge Controller (Bluetooth): Energy Controllers - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

You will love the Bluetooth. And with a 5 yr warranty, it’s a pretty easy choice.

 

[DJSmiley]

Or, if you don't need the BT and don't mind with a little harder configuration (but that has to be done only once) and are on a tight budget: the epever 1210AN ($65 or so)

The Victron is higher quality and much more user-friendly, but the Epever does a great job at a much lower price.