To make sense of this article, please read "Charging batteries - the problem" before reading this.
So how do we charge the habitation batteries effectively?
Basically, there are a few ways to do this.
1. Simplest, but least popular, is to join all the batteries together permanently, wired in parallel. The starter battery will always be at the same state of charge as the habitation batteries, because they are joined together, pulling together.
The habitation batteries won't take the strain of starting the engine, because the leads from the habitation batteries aren't thick enough to carry a lot of current.
The alternator only has one lot of batteries to look after, which is exactly what it is designed to do. The one snag is that if you run your batteries down to the point that the engine won't start, you are stuck. I think this is possibly a risk you can avoid by being careful. I have never, ever, run my habitation batteries low enough to be in that situation. But thise is one failure mode that could carch you out: if one of your batteries develips a fault that makes it self-discharge (old batteries often do) it will bring all the other batteries down too.
2. The second approach (the one I prefer and I use) is to install a battery to battery charger. This is a device that takes power from the starter battery, and passes it to the habitation batteries at the appropriate voltage and currennt for their state of charge.
These things work brilliantly, are easy to install and are a fit-and-forget setup. The biggest snag is the cost. Battery to battery chargers cost between £100 and £500 (or more). I have had two Sterling battery to battery chargers, and I like them although both of mine have failed, one of them beyond repair. Their biggest drawback is that they have astonishingly noisy cooling fans.
I replaced my working Sterling B2B unit with a Redarc one, made in Australia. It has no fan, so is silent. Despite that, it doesn't seem to overheat.
Other leading brands are Ablemail and Victron. I've not used them, so can't comment on whether they are any good.
3. The third option is more or less a DIY battery to battery charger. Instead of paying hundreds of pounds for a specialist unit, buy off-the-shelf components. Have an inverter that switches on when you start the engie, supplying power to a mains-powered smart battery charger connected to your habitation batteries.
The snags with this arrangement are a slight loss of efficiency in converting to and from AC mains voltage, and the undeniable fact that there is more to go wrong.
The avantage is that it is likely that you could buy everything needed for about £100.
So how do we charge the habitation batteries effectively?
Basically, there are a few ways to do this.
1. Simplest, but least popular, is to join all the batteries together permanently, wired in parallel. The starter battery will always be at the same state of charge as the habitation batteries, because they are joined together, pulling together.
The habitation batteries won't take the strain of starting the engine, because the leads from the habitation batteries aren't thick enough to carry a lot of current.
The alternator only has one lot of batteries to look after, which is exactly what it is designed to do. The one snag is that if you run your batteries down to the point that the engine won't start, you are stuck. I think this is possibly a risk you can avoid by being careful. I have never, ever, run my habitation batteries low enough to be in that situation. But thise is one failure mode that could carch you out: if one of your batteries develips a fault that makes it self-discharge (old batteries often do) it will bring all the other batteries down too.
2. The second approach (the one I prefer and I use) is to install a battery to battery charger. This is a device that takes power from the starter battery, and passes it to the habitation batteries at the appropriate voltage and currennt for their state of charge.
These things work brilliantly, are easy to install and are a fit-and-forget setup. The biggest snag is the cost. Battery to battery chargers cost between £100 and £500 (or more). I have had two Sterling battery to battery chargers, and I like them although both of mine have failed, one of them beyond repair. Their biggest drawback is that they have astonishingly noisy cooling fans.
I replaced my working Sterling B2B unit with a Redarc one, made in Australia. It has no fan, so is silent. Despite that, it doesn't seem to overheat.
Other leading brands are Ablemail and Victron. I've not used them, so can't comment on whether they are any good.
3. The third option is more or less a DIY battery to battery charger. Instead of paying hundreds of pounds for a specialist unit, buy off-the-shelf components. Have an inverter that switches on when you start the engie, supplying power to a mains-powered smart battery charger connected to your habitation batteries.
The snags with this arrangement are a slight loss of efficiency in converting to and from AC mains voltage, and the undeniable fact that there is more to go wrong.
The avantage is that it is likely that you could buy everything needed for about £100.