12V surge protection for solar PV

[mikepepler]

Fuzzy - yes, mine's the Mass Sine 12/2000-230V. It's about 1m from the charge controller (which is the source of the power making the voltage spike), and it's about another 1m from there to the battery. 50mm2 cables in straight runs. There is always going to be some inductance and capacitance in any cable, but I doubt these are long enough for it to be an issue.

Chris, I have it set up in 'search mode', so it uses less than 1W, pulsing the mains output briefly every 2 secs. If it detects a load then it stays on. The only loads I leave connected are fridge and freezer, both of which use mechanical thermostats so when they are off they really are off. This is why I also have the 180W inverter, for the always-on loads. It only uses a couple of watts in standby, bu in practice is always supplying power to the router. (I tried turning that off overnight but BT's hardware at the cabinet interpreted this as a poor quality line and slashed the broadband speed!)

[kenneal - lagger]

Mike, could you put the fridge and freezer on a time delay switch so that if they go off they have time to discharge the pressure before restarting. We've got our freezers on multiple delays so that they come on individually after a delay of about 15 minutes after the genny starts up. We have a macerating pump on the grey water sump which often comes on with the genny so we don't want five freezers coming on at the same time. This wouldn't be a complete fix but it would protect your white goods.

[mikepepler]

Thanks Ken, I was wondering if this was a possible workaround, pleased to hear it works in practice.

I measured the fridge and freezer's power consumption last night, which was as follows:

Fridge:
- startup ~450W
- running ~40W
- compressor stall ~450W for 30 secs, after which a cut-out operates for a minute or two

Freezer:
- startup ~850W
- running ~70W
- compressor stall ~480W for about a minute, after which a cut-out operates for a few minutes.

What happens is that when a voltage spike causes the inverter to trip out and reconnect, then the fridge and/or freezer ends up in a compressor stall - and the cut-out operating causes another inverter trip when the load disappears.

Having taken another look at Victron's product range, it seems they have stuff available now which they didn't when I was last buying an inverter. I'd been assuming my only choice was to replace the Mastervolt with another 2-3kW inverter, which would cost a lot. However, it seems that if all I want to handle is the worst case of the fridge and freezer starting simultaneously, then then something with a surge capability of ~1300W would be fine. I can then keep the Mastervolt as it is for running the big stuff like the washing machine. So I could either get:

2x Phoenix VE.Direct 500VA https://www.victronenergy.com/inverters ... 50va-500va

1x Phoenix Inverter 800VA https://www.victronenergy.com/inverters ... 0va-1200va

The second option is slightly cheaper, and can cope with up to 17.3V input (17V for the first one). It's eco-mode isn't programmable like the first one is, but that wouldn't be a problem for my planned use.

So the question really is: Is it worth spending £275 on an additional inverter simply to get the batteries fully charged in cold weather.... It certainly won't pay for itself in normal operation, as I still have access to the grid. In the event of a power cut it would start to earn its keep, but we've only had the briefest of outages since I installed the first version system nearly 6 years ago...

(p.s. I just found the second option above a lot cheaper at £187, albeit with a Schuko socket)

[Pepperman]

How big is the Mastervolt inverter, and does it have an 'always on' load? I've seen some ~3kW inverters that consume 20-30W even when there's no load?

I've been thinking one solution would be to have something around 500-800W on all the time for lighting, IT, fridge etc. and a 2nd inverter around 3-5kW which is only switched on when needed for the big stuff like induction hob, power tools etc.

Our inverter/charger (Mastervolt Mass Combi) has quite a chunky background load unfortunately which really saps the batteries, especially in winter. It claims low consumption but I don't believe the specs.

When we move out of the boat back on to dry land and do a proper off grid set up I'm going to switch to 12V refrigeration and go virtually entirely 12V with an inverter solely used for higher 230V loads. By then USB-C with Power Delivery should be standard so it should make mostly DC living very doable.
With a decent sized PV array and batteries it should be possible to get close to 100% solar with that approach.

[clv101]

When we move out of the boat back on to dry land and do a proper off grid set up I'm going to switch to 12V refrigeration and go virtually entirely 12V with an inverter solely used for higher 230V loads. By then USB-C with Power Delivery should be standard so it should make mostly DC living very doable.
With a decent sized PV array and batteries it should be possible to get close to 100% solar with that approach.

I'm flip-flopping on the suitability of 12V in a 'house scale' environment. Cable loses/costs are not insignificant when thinking about 10s of meters of cable.

For starters, any reasonable sized battery store is going to be at least 24V but more likely 48V. So the options are; an AC circuit from inverters, a 48V DC circuit or a 12V circuit from a DC-DC converter.

I've also seen people running a separate (smaller) 12V battery bank (as well as 48V) maintained from an AC charger from the inverter. This means 12V is available all the time, and the inverter is only switched on when it's specifically needed for something.

[adam2]

I am aware of one very large system that uses 3 wire DC at 12/0/12 volts, this voltage being chosen to permit of 12 volts for lighting and various small appliances with 24 volts for refrigeration and inverters.

This was a good choice at the time as high efficiency lighting was largely 12 volt.

Serious consideration is now being given to changing the system to 3 wire DC at 24/0/24 volts, or possibly 26/0/26 volts.
Although there is a fair bit of legacy 12 volt lighting and equipment, much of this could be changed to 24 volt.

[Pepperman]

Yeah to be fair I'm thinking DC rather than 12V specifically. It'l' probably need some stepping down to lower voltages in some areas.

The cable run length is certainly a potential issue but I'm happy to overspec and invest in decent guage cable where necessary. The key will be careful design so that the battery is close to the heavy loads. My current thinking is a central core to the home where the battery would be located (well within the thermal envelope of the building - ventilated of course).

To be honest there won't be much in the way of heavy DC load as I would be aiming for maximum efficiency. AC can take the occasional heavy item.

[fuzzy]

The other solution is to find out what things actually need to run. LED lighting has various DC options if you string LEDs yourself. Most AC equipment is just 5 - 40V DC stepped down and rectified from AC, so modifying stuff for direct from DC makes sense. I have aways been disappointed at the price of 12V fridges and freezers, but maybe someone can commercially replace AC compressor motors with low DC options.

[clv101]

To be honest there won't be much in the way of heavy DC load ...

Indeed, the fact that potential DC loads wouldn't be that high is what's leading me to a high quality, low power inverter, on all the time.

[mikepepler]

What are your biggest loads Chris? I started out with some 12V stuff, but in the end have done everything at 230V, as you can use standard appliances. Our biggest occasional loads are washing machine (~800W spin), vacuum cleaner (~900W) and iron (2kW). I think we'd have struggled to do them on a dc system.

BTW, on the surge issue, I've ordered a new inverter as I found a place doing them for about £100 less than normal: http://www.batterymegastore.co.uk/produ ... 10200.html