Shore charging questions

With the snow and overcast conditions recently in the PNW, I've needed to connect to shore power to recharge the system after consecutive 3 day/2 night out ski trips. Summer and fall were recovered/maintained quickly by the 400W solar alone. The accessible power at home is a 15A service, which is typically taking about 36 hours to go from 80% to 100% SOC. Current draw is from several LCD lights, 2 fans, recharging 2 phones and Espar D2 running most of the time.

4x100 Ah Windy Nation AGM batteries
Victron 712 Battery monitoring system
Victron Multiplus 12/3000 Inverter/charger
12AWG connecting wire between shore inlet and inverter

1. Does it matter (other than the time it takes) whether you shore charge from 15A, 20A or 30A service for the health of the batteries? Multiplus manual lists AC input current limits from 3A - 50A. Also states "for maximum battery life, a charge current of 10% - 20% of the capacity in Ah should be applied. Example: optimal current of a 24V/500Ah battery bank: 50A to 100A".
My equivalent would be 12V/400Ah: ?A to ?A (I'm not sure of the formula used to calculate the 10-20% amp range).

2. When charging from 15A service does the length of the extension cord or gauge of the wire play much of a role? I've used both 25' 14/3 and 100' 10/3. Thought about getting a 25' 10/3 if it helps.


2008 2500 170" EXT
You need to refer to battery's manual for the correct charging spec's and guideline first or foremost.


Well-known member
The charger outputs 120A.
Output power = 120A * 14.4V = 1728 W

Input power = Output power / efficiency
Input power = 1728W /0.8 = 2160 W
Input current = 2160W / 120V = 18A

That means 15A service is too low. You need 20A.

The length of ac cable and gauge plays a roll.
14 awg = 2.5 mOhm/ft
10 awg = 1.0 mOhm/ft

Line drop for 14 awg, 25 ft = 50 ft * 18A * 2.5 mOhm/ft = 2.25V
Line drop for 10 awg, 100 ft = 200 ft * 18A * 1 mOhm/ft = 3.6V

That means if you use 25 ft length, 14 awg cable the voltage at the converter is 120V - 2.25V = 117.7V

The converter will need to work harder the larger the line drop. The batteries are not affected.

4 * 100AH = 400AH
Applied current = 120A/400AH = 30%

There's no problem charging at 30%
You need to refer to battery's manual for the correct charging spec's and guideline first or foremost.
Battery manual states:
Max Charge Current: 30 amps

Charge mode @ 77 degrees F (it's probably been around 35F in the van while charging)

Bulk 14.4V
Abs. 14.1 - 14.7V
Float 13.5V

I haven't been monitoring as it went through the charging stages, but did note this morning when it displayed 100% SOC it was 13.2V. What other battery information is needed?


Well-known member
Something doesn't sound quite right.

Going from 80-100% should take 3-4 hrs, not 30-40 hrs.

One place to look is to see if the temp compensation is working.

If the charger thinks that it is just doing finishing state charging, and there are significant loads, perhaps that is slowing it down.

My van has a similar pack, 400 amp hrs of lifeline s wired 48 volt x 100 amp-hrs. The charger I am using is less powerful but could easily go from 50% SOC to completely full in 4-6 hrs.

Obviously lifeline s are different than windy nation but that is way too long.


New member
Does it matter (other than the time it takes) whether you shore charge from 15A, 20A or 30A service for the health of the batteries? Multiplus manual lists AC input current limits from 3A - 50A. Also states "for maximum battery life, a charge current of 10% - 20% of the capacity in Ah should be applied.
Quality AGM can accept a **much** higher current rate.

For many makes, 0.2C would be the **minimum** rate for good longevity.

For some 0.4C, and again that's a minimum, even 0.6-0.8C will do no harm, lead in general is self-limiting and vendor "max current" specs a legal CYA fiction.

In short go for it,

get a 50A 240V circuit installed

just don't go high nor over long; keep voltage at the vendor's to Absorb spec, and stop charge at their endAmps spec.

Ideally, adapt your charger to accept J1772 input from EVSEs out on the road, just don't hog them when genuine EVs are queuing up or they could start blocking us.
Last edited:


New member
The problem isn't the shore power you are connecting to, something is wrong with the charging settings. Check to make sure you have the correct charge rate and voltages set for your batteries. As calbiker pointed out your 15A/120V service may or may not be able to charge at the maximum supported 120 amp rate, but it can certainly get close. You should be able to charge your batteries from completely empty to full in a few hours.


New member
His rig only has 12awg from shore power plug to inverter/charger. That would limit him to 20A max unless he also wants to learn how wires overeat and start fires.
Yes obviously the infrastructure from start to finish needs to support 20% more than the maximum current it will ever see.

Did not think that needed stating, sorry. And thanks!

PS no extension cords when you get to very high currents. Since you need a pro to put in that 240 circuit, do your bits first and get them to inspect your whole setup while they're there.

Not officially take any responsibility of course, unless they want to charge over say an hour labor extra.
Last edited:


Active member
Also you said charing in the PNW after ski trip...what is the temp of the batteries when attempting charging? LiFepo4 systems and cold temps no workie.


New member
Until the cell interior itself gets below freezing, it's just a matter of charging slower.

0.1C should be fine from freezing

above 10-15°C go to a 0.2C rate,

25° should be fine for 0.3C
john61 ct and Shawn182 - yes, I recognize going to 50A (even 30A) from shore to charger I would need to replace the 12 awg wire and the inlet on the side of the van. Lifepo4 batteries not working so well in the cold is one of the reasons I went with AGM. However I didn't buy the separate temperature sensor for the Victron because I didn't completely understand the set up. Now I'm rethinking it and will probably order one so I have compensation and data points. Without the sensor I'd guess the batteries were around 30 degrees F when charging.

I'm going to need to do some studying of the charger manual to double check settings. I can't remember the ones I input, but I know I didn't change much from factory settings.


Van Guru
Set your charger to 50% rate (60A) using the dip switches. (you have 4 batteries so each should get 15A) 60A * 14.4 is 864 watts which is going to draw about 8A at 120V. Your 12 gauge wire and 15A outlet should be able to handle that just fine. Make cord to van as short as possible and monitor the AC input voltage at the charger. Definitely install the temperature compensation sensor on the batteries.

All the best,
541 490 5098
Last edited:


New member
You should absolutely get the temperature sensor for your batteries since you are using them in cold climates. The standard charging voltages provided for batteries are for 70-80 degrees, AGM batteries need substantially different voltages in near-freezing temperatures which the controller will automatically adjust once you install the sensor.
I've reviewed the install and manuals, and found several points to address (all items that you folks have pointed out).

Settings - the charger is set at factory default settings: charging current 75% of maximum and input limit is 50A

Temperature sensor - not installed, but I found it in my parts bin. I can't say why I missed it at install, but that is now correctable.

Part of my lack of understanding was mixing up the temperature sensor (TS) for the charger and TS on the battery monitor (which is a separately ordered part). So TS on the charger adjusts the flow to compensate for batteries temp during charging. While the TS on the monitor allows you to know what the battery temperature is, but doesn't modulate temperature. I think this is why people see the TS on the BMV 712 to be optional. Is this correct?

I've only used shore power twice and both times were in cold weather, so first step in to install the TS. Then I'll charge when needed and monitor the system to see if I need to change settings. Installing a higher amp house circuit will need to wait for spring. I also need to think about versatility. What will be my potential power sources since we almost always do "urban stealth" or dispersed camping.
Last edited:

Top Bottom