Question - now that winter is gere my big solar no longer replaces the power I use daily from my big battery bank - so what 230v charger should I install?
My suggested answer ..
It depends on how big the battery bank is ....
When you have a lot of battery and solar, then winter comes along, then as you say, solar starts to fade, so you need other sources. I have been living with a 600ah lithium bank for 2 years now and experience exactly the same thing. My attitude to 230v charging is that I want a full charge from an overnight plug in - which basically means a minimum of 12 hours. So the maths is simple - 600 / 12 = 50, so to charge a 600ah bank from zero in 12h I need a 50a charger. A 50a charger isn't cheap, so I am willing to compromise - the Victron 30a is a great charger, so 600 / 30 = 20 ... Is this a fair compromise? I think so, I will rarely arrive at EHU with a 100% empty battery - it will likely still have up to 100ah left, and if using a camp site or visiting a friend we will try and arrive mid afternoon, and will rarely leave before midday, so that's easily 20 hours ... so the arithmetic is easy, and made easier by using the app on your smart battery or smart shunt.
And for a smaller battery - ie 300ah - the sums are again easy - you can probably get away with 20a, and these are now under £100.
But ... you also have to deduct what you will be using while you are charging. Example - I consume 6a per hour with TV lights and computer on, so between 6 and 12, plus a bit in the morning, that will be a reduction in charge of around 50ah, so you have to also take that into consideration.
Lifestyle is another consideration. I full time and hate plugging in, plus campsites are expensive, but we still need laundry and pitstops, so I tend to combine everything in one go - the aim is to leave a campsite in winter after just one night with full batts and clean clothes! Plus you can add back in driving time and alternator charge - and again the app tells you what is what and when you will need to seek charge.
WHAT CHARGER?
Generally speaking, most Lithium installs I do I install the Victron 30a. I am not a Victron fanboy, but I rate their chargers as pretty much best value for money for a big lithium bank. They are quiet, they have a no fan mode at 50% reduced power, they have an app, they are well built, easy to connect, fused internally .... but if you install one in a classic Hymer you must not use the original Hymer charger cable without modification. if you do the power will go through the hymer fuse box, and strom meter and is in excess of their rating, plus the path is lossy. I can advise on this, but if your charger is next to the battery then it's a 10 minute job to connect directly. And if for some reason you want mega fast charging then you can paarllel up 2 Victrons quite happily. If for some reason you don't want Victron, I can advise on other makes.
AN ALTERNATIVE TO CHARGERS
Also if you are a self installer and like doing this stuff, you can also save money by instead of buying dedicated chargers, buy inexpensive 230v/24v power supply unit(s) and connect the 24v output to the panel input of your solar controllers. Then they think the sun is shining all night and you should get full output, complete with lithium profile. That's what I have been doing, and it works. The only downside is that is complicates the cabling - you have to have a method of switching between 24v PSU and panels. But it's cheap - 400w PSUs are less than £30 on Amazon, and they are designed for 24/7 use in LED lighting installations. But they also have fan noise. It is an option, but if you don't understand any of this paragraph, then just buy a charger!
EHU POINTS AND TRIPS
Tripping an EHU point is not an issue for battery charging - if you have a 30a charger, that's 30a x 13v = 390w. Divide that by 230v, and it's well under 2a at 230v. Even if you had a 60a charger it's not a problem. Most EHU points are 13a - that's 3000w, and even the most measly ones are 6a = approx 1500w. It is only when you start plugging in high power devices like kettles, fan heaters, aircon and big airfryers that you start to trip out EHU points.
OHM'S LAW
A basic understanding of Ohm's Law is invaluable when dealing with 230v and 12v - chargers and inverters. Ohm's law (look it up!) is just a simple calculation. Watts equals volts times amps. Amps equals Watts divided by volts. Volts equals watts divided by amps. So you only need 2 of the 3 values to calculate the other. And the thing to remember with 12v is that the more amps at 12v, the bigger and thicker the cables need to be - because it is the amps that need the copper. And conversely that's why you only need thin cable in a house, because a house is 230v. So to power a 1000w appliance in a house you only need a 4a cable, which is much thinner.
The watts are constant, the volts and amps change. So to run a 1000w airfryer (look at the label to get the watts) through a 12v inverter - it's 1000 / 13v = 80a (always round up) .... so that means you want cabling good for 80a .... but good practice at 12v is to have a margin of at least 50% preferably 100%, so things run cool and not at the max ... so for a 1000w load I would use a 2000w inverter and cabling good for around 100a, rounded to the nearest size. This is how you use OHM's law to size a 12v system. But safety margin is not an issue when sizing chargers - if you buy a 30a charger, that is what you get, so the only issue is cabling - you want a cable that can pass 30a with 2% loss or less ... chargers are usually supplied with cable, so use that if possible. But if you need to extend it more than double, then you need to recalculate.
For sizing cables I always use the online calculator at 12vplanet
https://www.12voltplanet.co.uk/voltage-drop-calculator.html
Search for Victron IP22 12/30
400w 230v to 24v DC power supply (artificial sun!)
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