Central heating pump off 12V?

[Peasgood1]

I know there are some clever folk on here when it comes to electrickery so I thought I would ask.
I am lucky enough to live out in the sticks, one of the few downsides is that the electric supply can be a bit iffy at times.
All my heating is via a wood fueled AGA type thing and pumped with a standard central heating pump. My concern is the electric going off when my log fire is at full chat and me not being there at the time. In theory it should be fine as the radiators upstairs will act in a capillary fashion if no pump, plus there is one rad up there dedicated to that purpose. I still wouldn't like it to happen with me not there all the same. (if I am there I can run off some hot water from the tank.

Anyway, my theory is that if I have a leisure battery with a mains trickle charger to it and an inverter off the battery to power the pump if the supply goes off I will be OK.
Any of you clever chaps able to offer a schematic of the above or even advise on a better way to do it maybe?
I have thought about sorting it many times but never got round to it. I heard on the radio today that the national grid is at full stretch these days, better i get it done. Also heard there is a chance of a bad winter again (there is always a chance) Would like to be able to run my heating if the electric goes off.

 

[rustic]

Years ago we had a coal fired open fire with a 16" back boiler that gave us hot water, and fed a few radiators, but you had to manually switch the pump on.
On many occassions when we were out, the fire had nearly gone into melt down, producing steam and banging away...:doh
What I did was to put a n/o normally open thermal switch of approx 60 c on the feed pipe going upstairs. When the fire got hot, the water in the pipe got hot, and the thermal switch closed the contacts that then switched on the pump and we had hot water in all the radiators.
So this is something you could utilise.
For power fail detection, you need a mains powered relay that is normally connected to the mains, when the mains fails, the N/O contacts on the relay close, this could then supply an inverter that drives the pump.
But the contacts would need to be suitable for the high current.

NOW control of the pump can be an issue, regarding electrical safety, if you want to utilise the same pump, then you need to isolate the pump from the mains, both Live and Neutral, with relay contacts and then connect to the inverter output.
Quite easy to do, BUT you must avoid the risk of back feeding the inverter output to the mains and vice versa. Fusing is also important too, and of course cable size.
Earthing for safety, so quite a few considerations.

This can be all be achieved using a mains powered relay, with three sets of changeover contacts, however as the contacts will be supplying mains live neutral, Inverter live and neutral, and 12 volts feed for the inverter, there is a GREAT risk of cross connection, as the electrical clearances are critical.

Better to use two relays, one to switch mains, and one with heavy duty contacts to switch the 12 volt feed to the inverter.
Both relay coils will need to be 240 volt ac.

Certainly dooable..:thumb2

Rustic

 

[zippy656]

Why not just a 12v pump, no inverter would run longer than a 240v running from 12v

Oily bits might be of some help sure he had 12v pumps when i was there last

 

[trophymick]

We use a small generator for the central heating pump when the electric goes off, one of the perks of country life.:thumb2

We have a Charnwood multi fuel fire/boiler.

 

[solarman216]

so easy to do, you just need an inverter for the pump, now pump will be around 45 watts so a low power inverter will be fine, say 300, as the off load demand will be low, and you just run the pump from this inverter all the time, via a relay if it is controlled by some external source like a stat on the fire, the inverter will be powered from a battery that you will need to calculate the capacity for the longest power cut likely and a charger that will match the pump power plus a bit say 10%, this way you have no issues with mains and inverter conflicts and guaranteed pump power whatever, Rick

 

[rustic]

We use a small generator for the central heating pump when the electric goes off, one of the perks of country life.:thumb2

We have a Charnwood multi fuel fire/boiler.

Better if it was auto start though, should the power fail when you are away.

We also have a generator, and we manually connect that to the house in power cuts and we are the only house in the village with power, the neighbours double check their fuses, "well his power is OK it must be us..." :augie:augie:augie

The most important item is the central heating controller and pump.

 

[Peasgood1]

so easy to do, you just need an inverter for the pump, now pump will be around 45 watts so a low power inverter will be fine, say 300, as the off load demand will be low, and you just run the pump from this inverter all the time, via a relay if it is controlled by some external source like a stat on the fire, the inverter will be powered from a battery that you will need to calculate the capacity for the longest power cut likely and a charger that will match the pump power plus a bit say 10%, this way you have no issues with mains and inverter conflicts and guaranteed pump power whatever, Rick

That is more like what I had in mind.
The pump doesn't normally run for all that long. Without actually doing the calculations I am confident the fire will go out before the battery goes flat. A different matter if I want to run the heating and the electric is off for a day or two. TBH that would be very unusual.

What sort of relay do I need for the above and what type of charger too? I assume the charger has to be of the type that turns itself off when the battery is fully charged. Do they call them smart chargers?

 

[rustic]

Numax do a good 10 amp charger, which is a multi stage charger, that starts up without pressing any buttons once the power is re-connected. These can be connected ALL of the time, as the charge rate drops to suit.

The "Ring" version and like many others, requires button pressing after each power loss, so this is essential to you, otherwise a very brief black out of a second or less will disable the charger, then a few hours later you have no pump...:doh

I have two Numax chargers on the boat, one for each 100 Ah battery, as we only get occasional electric hook up, so time is of the essence... and the outboard doesn't put out that much, and we also have 30 watts of solar power.
Now there's a thought, if you could charge with a solar panel...:nenau

Battery wise, with the calculations, I wouldn't discharge the battery beyond 50%

As a quick guide, without showing the calculations, a new 100aH "leisure" or "marine" battery, taken to 50% discharge, will run a 55 Watt pump through say a 300 watt inverter, for approx 10 continuous hours.

If you want 20 hours, double up the battery.:thumb2
Also consider that the battery will deteriorate year on year, and after 5 years the battery might only be able to hold half the charge, so may only give 5 continuous pump hours. At this point, I guess Rick will chip in with more advice as he is the expert, so only take my advice as a guide.:thumb2

For the relay, there are octal base relays with two changeover contacts, some have three changeover contacts and have 11 pin bases.
The relay plugs into the base like the old valves:doh and generally have 10 amp contacts. The coil voltage can be ordered as 12 volt DC or Mains ac, depends how you want to control the pump.
I would assume you would do the control at 12 volts DC, put in the thermal switch as per my earlier post and you will have a fully automatic control system.

These relay bases have screw connectors and have good clearance between connections, so are ideal for mixing the separate voltages.

I think that Rick is right about keeping the voltages separate, this way with the inverter on all the time the pump is needed, as per my original post, you would really need to know what you were doing to be safe under any fault conditions.

As a fall back, have the pump plugged into the inverter with a 13A plug type, so IF or when... the inverter breaks down, you can still use the pump as long as you have mains electricity.:thumb2

With this bad weather coming, you will probably need the circuit very soon.

best regards,

Rustic

 

[Peasgood1]

Excellent stuff, thank you for your help folks.

So I need a 100Ah leaisure battery, a "connect & forget" charger and a 300W inverter.
Can I just connect them all together,plug the pump in and leave it? What I really want to know is if the charger being on when there is demand on the battery is OK.

What was the relay for? there isn't one there at the moment. The controls are very simple, there is a pipe stat on one of the pipes that comes out of the boiler, when that pipe reaches a certain temperature the pump comes on. The stat just acts as a very simple on off switch. It has been like that for 5 years or so (since I put it there)

 

[zippy656]

Where the pump is connected to 230v,

fix plug and fit into inverter.

Connect inverter to battery

Battery to charger

Charger to where pump USED to be fitted


Bob's your dads brother

 

[solarman216]

the relay connects the pump to the inverter when the relay coil gets power from the thermostat that controls the pump now, this makes sure that the mains coming from the stat is isolated from the inverter and pump, if you are unsure of this then I suggest you get an electrician in to wire it for you, it is an easy way to blow your inverter if you get it wrong, Rick

 

[solarman216]

Where the pump is connected to 230v,

fix plug and fit into inverter.

Connect inverter to battery

Battery to charger

Charger to where pump USED to be fitted


Bob's your dads brother

the flaw with that zippy is the pump will run continuously and the charger will only come on when the pump should run, = flat battery in a short time, Rick

 

[zippy656]

I ment just 230v feed

Switching is still from the stat.


So pump runs when needed.

Battery always charged, unless power cut

 

[solarman216]

I ment just 230v feed

Switching is still from the stat.


So pump runs when needed.

Battery always charged, unless power cut

that is where you need the relay, to connect the inverter to the pump only when the stat says so, Rick

 

[Peasgood1]

The only "mains" in the stat is from the pump plug. Plug that into an inverter instead and it is then isolated from the mains.
The pump is plugged into the mains at the moment via a standard 3 pin plug. The feed from this plug is switched by the thermostat between the plug and the pump. So if I take the three pin plug out of the socket there is no mains supply to either the stat or the pump.

Can't I just plug this three pin plug into the inverter instead? Which I think is what Zippy meant.

From Rustic's calcs I reckon 10 hours continuous running would amount to a good few days use. The pump doesn't run a great deal really unless the fire is flat out. This usually only happens if my girlfriend is here for the weekend and is keeping the fire fully stoked. (a weekends worth of innuendos in there somewhere lol)

 

[solarman216]

No no no no no, you need fail safe operation with a solid fuel fire, what you are describing is remove pump plug from mains and put it into inverter, great but who is going to do it if you are not there, boom, you have to have the relay to switch the pump on when the fire reaches a set temp, no ifs no buts it is the only simple way to do it, Rick

 

[zippy656]

Ah, time to have a think

 

[Peasgood1]

No no no no no, you need fail safe operation with a solid fuel fire, what you are describing is remove pump plug from mains and put it into inverter, great but who is going to do it if you are not there, boom, you have to have the relay to switch the pump on when the fire reaches a set temp, no ifs no buts it is the only simple way to do it, Rick

If there is a power cut as things are now the capillary action of the system is the failsafe. Same as any solid fuel system. As I said very early on in this thread there is a radiator in the system dedicated to this purpose and in addition to that the water does circulate through the heating (rather than just the domestic hot water) anyway.
I admit I would be worried if the electric went off when the fire was at full bore but it is designed to cope.

What I have now goes mains>stat>pump, all I am suggesting is going inverter>stat>pump. Simply plug it in the inverter instead of in the mains socket. I am not bypassing the stat nor am I risking mains going down the plug into the inverter, the only electric in the system is out of the inverter.

The only possible issues are there is no relay in the system now, the stat switches the mains supply. It is rated to do that but I accept a relay would be belt and braces.
The only other thing I wasn't sure of was if the charger would be OK if it was connected to the battery and the pump came on. That isn't going to damage the charger is it?

 

[Peasgood1]

This is how it is. All I was proposing was unplugging from socket and plug it into the inverter instead.

 

[solarman216]

If there is a power cut as things are now the capillary action of the system is the failsafe. Same as any solid fuel system. As I said very early on in this thread there is a radiator in the system dedicated to this purpose and in addition to that the water does circulate through the heating (rather than just the domestic hot water) anyway.
I admit I would be worried if the electric went off when the fire was at full bore but it is designed to cope.

What I have now goes mains>stat>pump, all I am suggesting is going inverter>stat>pump. Simply plug it in the inverter instead of in the mains socket. I am not bypassing the stat nor am I risking mains going down the plug into the inverter, the only electric in the system is out of the inverter.

The only possible issues are there is no relay in the system now, the stat switches the mains supply. It is rated to do that but I accept a relay would be belt and braces.
The only other thing I wasn't sure of was if the charger would be OK if it was connected to the battery and the pump came on. That isn't going to damage the charger is it?

yes you are correct, if you have a fail safe gravity heat dump then inverter - stat - pump will work fine, Rick