HMV Barn Project

[Nowhere-Man]

... Should you not have a mains supply (Power cut), you can switch the inverter itself on and it will then supply 250 AC just from the car batteries ...

Car batteries? Why on earth would you use car batteries?

Car batteries are designed with one prime purpose - to provide a heavy current for a short time to start the car engine. After that, the load is taken up, in the main, by the alternator which also recharges the car battery at the same time.

What you need are so-called leisure batteries which are designed to provide power at a much lower rate than required for starting a car but to do so for long periods of time.

I'm afraid you jumped the gun a bit here by taking me so literally. By "car batteries" I simply meant "lead acid batteries".

Basically anyone who owns a yacht or narrow boat is going to know the difference between leisure and starter batteries. At least I hope they do.

Starter batteries as you say are designed for starting an engine. These are special batteries that are rated in CCA (Cold Cranking Amps). The system used in the eighties when things were a lot simpler was as follows:

2 or 3 House batteries that (if my memory serves me correctly) can supply about 300 Amp Hours.

Starter battery connected to system by a split charge relay. On turning ignition the alternator B+ supplies about 14 volts to all batteries but (when ignition is off), the starter battery is disconnected from the House supply. Actually I need to buy one of these. There is also the diode isolation system to prevent drawing from the starter battery but this does cause a small voltage drop in charging. I'm not sure how much a diode isolator is but I'm sure the fancy regulator you need for upgrade is still not cheap. So, I may settle for just a relay. I was looking into current ratings and automotive types aren't really suited (although people use them).

As to the way and means of coupling shoreline and inverters, I do know it's important not to mix outputs. I'm not yet sure how I plan to make a system but imagine I may be converting to solar power.

At the moment, I have replaced the inverter/charger with a 15 amp fuse and have it charging up a clapped out battery that had dropped to 9.5 volts. I put a plug on the inverter as it's shown in the booklet and just plugged it in. So, the inverter is secondary and used as an appliance. The battery is reluctant to charge. It may or may not have sulphated but sometimes it's possible to get a charge. Time will tell. I have to step over it as it's on the floor at the moment charging.

One thing I discovered was I think it's a ferro resonant charger because the booklet shows a max current of 10 amps at charge yet lower voltage. When the voltage goes up to 13, current drops. There was a debate with a friend about cable size but I ended up fitting a very high amps cable, mainly to accommodate any surge or high load across the inverter.

This is a modified sine wave unit. Not sure how my radio would work on it.