Solar dump load

wakey_wake · May 1

7 minutes ago, blackrose said:

The SSR is rated at 40A so surely it can sustain 4-8A?

The SSR can, yes.

I was replying to

3 hours ago, blackrose said:

The SSR is connected to the MPPT relay terminals. Surely the MPPT relay terminals can't switch AC? Hence the DC to AC SSR.

so I thought you were pointing out that the SSR is needed because the MPPT relay can't switch the load directly.

7 minutes ago, blackrose said:

I think the quality of any electrical components is important, but since you mention flexibility, is the relay in the method I posted in the OP (shown below) that others are using any more flexible than the Victron relay in my MPPT?

Picture is broken for me, but in your OP the PDF says

Quote

Smart Relay: [12V Voltage Detection Charging Discharge Monitor Relay Switch Control Module]
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=12V+Voltage+Detection+C
harging+Discharge+Monitor+Relay+Switch+Control+Module&_sacat=0
As an alternative to the 12v smart relay for those with 24v systems and with no access to a 12v supply (for the
working power interface on the smart relay); this relay may be used instead. Though I have not used it myself as I
had access to a handy regulated 12v supply.
Alternative Smart Relay: [Multifunction Cycle Delay Timer Relay Module for timing and counting]
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=Multifunction+Cycle+Delay
+Timer+Relay+Module+for+timing+and+counting&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=12V+Voltage+
Detection+Charging+Discharge+Monitor+Relay+Switch+Control+Module
However, there is a YouTube video detailing its review and setting up.
https://www.youtube.com/watch?v=eT3Ie1bMkJk

(ugh, format broken)

Without seeing the configuration options for the Victron, I don't know. I believe Victron would do what you need, but I also said there will be only minor changes if it turns out not to.

Hmm and the first link lists boards which seem to provide digital voltage setting, but no information about hysteresis or anything else.

...so I have insufficient information on either to make a useful response.

Returning to MtB's original point, another way to provide effective hysteresis would be in the time domain: while the required voltage is reached, activate the immersion for the next 30 seconds. This way if the voltage drops you don't immediately stop the heating.

One experiment you can do fairly easily before breaking into the mains circuits is to configure the MPPT relay now, and connect

+12V --- fuse --- Common

Normally Open --- lamp or LED strip --- gnd.

Then when the light comes on, you switch the immersion heater on manually and see how the MPPT relay responds.

blackrose · May 1

2 hours ago, wakey_wake said:

The SSR can, yes.

I was replying to

so I thought you were pointing out that the SSR is needed because the MPPT relay can't switch the load directly..

Yes that's correct.

2 hours ago, wakey_wake said:

One experiment you can do fairly easily before breaking into the mains circuits is to configure the MPPT relay now, and connect

+12V --- fuse --- Common

Normally Open --- lamp or LED strip --- gnd.

Then when the light comes on, you switch the immersion heater on manually and see how the MPPT relay responds.

Yes that's not a bad idea. Thanks.

blackrose · May 3

This is the circuit diagram I've drawn.

In terms of fuses I already have the mains AC fuse fitted, from memory think it's 5A. What about the 12v fuse, any ideas on what rating that should be? Do I need any other fuses on either DC or AC sides of the system? Should there be a 5A fuse between the SSR and AC regulator?

jonathanA · May 3

I don't really see why your using the burst fire thing or the SSR to be honest. Yes I can see being able to wind the power down from 1KW might be useful if you regularly only have 500w of "spare" but not sure that's really an issue in the lithium world. Its not like there is some link between the mppt and the power controller. You will have to twiddle the pot to change the power delivered to the immersion, so seems a bit pointless to me.

I'd stick in a relay Instead of the ssr and try it like that then add the burst power thing later on if you find you need it.

Also I'm not sure about shoving mains back down to the burst fire thing. Probably better to have the changeover at the immersion selecting between direct mains or solar controlled supply.

Edited May 3 by jonathanA
Added a bit about dpdt position

wakey_wake · May 3

11 minutes ago, jonathanA said:

I don't really see why your using the burst fire thing or the SSR to be honest. [...]

I'd stick in a relay Instead of the ssr and try it like that then add the burst power thing later on if you find you need it.

I suspect an advantage of the burst fire thing over a cheaper phase chopper, but I don't have proof.

I don't see an advantage of the SSR over a mains-rated 12V-coil relay, except it's silent and has screw terminals.

That's irrelevant now because the hardware is on the boat and he wants to wire it up. 😀

1 hour ago, blackrose said:

This is the circuit diagram I've drawn.

Sorry to be fussy, but I would suggest re-drawing with

separate lines for L,N,E rather than a "combined line", else we may have misunderstandings,

more detail about the wiring of the DPDT switch: I think you'll want the incoming mains on the flying contacts,

draw the 5-core coming out of the regulator and then break it into cores in the relevant piece of hardware. Unless you found another solution to the single gland.

It might help to show how the SSR and regulator will be mounted and enclosed. (I'm terrible at that stuff.)

The DPDT as shown suggests you doubt the reliability of the new parts and want the option to quickly switch it back the way it was.

Depending on your motives or expected habits, you might keep the regulator in on "manual" mode. I presume it has a 100% setting?

Then it would only need a SPST switch to short out the SSR, and you have the option of doing the equivalent at 12V instead. If you might later venture towards a one-shot "heat my shower" button, or Raspberry Pi linkage, then this is the way and small diodes are your friend.

Be aware that the regulator and SSR will still be live when the DPDT as shown is in manual mode. The SSR won't mind, but the regulator might and your fingers certainly would.

1 hour ago, blackrose said:

In terms of fuses I already have the mains AC fuse fitted, from memory think it's 5A. What about the 12v fuse, any ideas on what rating that should be? Do I need any other fuses on either DC or AC sides of the system? Should there be a 5A fuse between the SSR and AC regulator?

12V 1A will be plenty. You can go higher if the cable is thicker, and you'll want thicker cable so it's not fragile, but the SSR needs milliamps or less.

240V 5A seems fine for a 1kW heater. 👍

I can't see any benefit of further fuses. What would they be protecting? Where would the extra current be coming from or going to?

blackrose · May 3

3 hours ago, jonathanA said:

I don't really see why your using the burst fire thing or the SSR to be honest. Yes I can see being able to wind the power down from 1KW might be useful if you regularly only have 500w of "spare" but not sure that's really an issue in the lithium world. Its not like there is some link between the mppt and the power controller. You will have to twiddle the pot to change the power delivered to the immersion, so seems a bit pointless to me.

I'd stick in a relay Instead of the ssr and try it like that then add the burst power thing later on if you find you need it.

Also I'm not sure about shoving mains back down to the burst fire thing. Probably better to have the changeover at the immersion selecting between direct mains or solar controlled supply.

Being able to reduce the power draw of the inverter should be useful. I only have 910w of solar panels. Yes, I will have to set the AC regulator but if I decide to set it to 500w in winter for example, I only have to set it once. In summer I can reset it to 1kW. Both systems I posted previously (Post #1 and post #16) use AC regulators to reduce the draw of the immersion.

The SSR is a relay (Solid state relay).

I don't really understand your last paragraph.

3 hours ago, wakey_wake said:

I suspect an advantage of the burst fire thing over a cheaper phase chopper, but I don't have proof.

I don't see an advantage of the SSR over a mains-rated 12V-coil relay, except it's silent and has screw terminals.

Is there any benefit of a 12v coil relay over the SSR?

3 hours ago, wakey_wake said:

The DPDT as shown suggests you doubt the reliability of the new parts and want the option to quickly switch it back the way it was.

I have no idea about the reliability of the new parts, but it would seem stupid to install a new system without the option to bypass it. For example if I found myself over winter in a marina with mains hookup it might be useful to be able to run the boat from shore power and use the immersion from the mains. The system I posted in the OP has a bypass switch. Not sure about the guy's system in the video in post #16.

3 hours ago, wakey_wake said:

Be aware that the regulator and SSR will still be live when the DPDT as shown is in manual mode. The SSR won't mind, but the regulator might and your fingers certainly would.

What do you mean by "manual mode"? When the changeover switch is switched to "bypass" there will be no mains to the SSR or the AC regulator.

https://www.amazon.co.uk/Heschen-Universal-Selector-Changeover-Terminals/dp/B097T3DXV8/ref=asc_df_B097T3DXV8?

Edited May 3 by blackrose

GUMPY · May 3

1 hour ago, blackrose said:

Is there any benefit of a 12v coil relay over the SSR?

Not in my book there isn't.

wakey_wake · May 3

20 minutes ago, GUMPY said:

2 hours ago, blackrose said:

Is there any benefit of a 12v coil relay over the SSR?

Not in my book there isn't.

The purchase price. Possibly power dissipation? Some are shown with a comedy pogo-like heatsink.

Both will have some 'on' resistance, but I don't if it will be significant under 4A(avg).

2 hours ago, blackrose said:

5 hours ago, wakey_wake said:

The DPDT as shown suggests you doubt the reliability of the new parts and want the option to quickly switch it back the way it was.

I have no idea about the reliability of the new parts, but it would seem stupid to install a new system without the option to bypass it.

It makes sense to test the kit when it's installed, check it's reliable, and then trust it; and if a part fails you know how to either service it or restore the previous operation. You're running both at well below their rated power so the only risk is voltage spikes - from a bollard, from an onboard motor, or the Angry Sky Pixies decide to visit.

It's also perfectly reasonable to want a switch to go "back to how it used to be", which does point to bypassing the regulator also.

2 hours ago, blackrose said:

What do you mean by "manual mode"? When the changeover switch is switched to "bypass" there will be no mains to the SSR or the AC regulator.

I refer to the DPDT bypassing the SSR+regulator as a "manual mode", e.g. for when you know the MPPT won't give you hot water of its own choosing but you decided you want it anyway, even at the expense of tomorrow morning's coffee and the defrosted food. 😉

ISTR one of the referenced designs had a three-way switch for this (on, off, auto) but if you've got the bits or already have a preference that way then it's just as good.

⚠️ the regulator definitely will be live, by back-feeding from the live immersion element. The SSR maybe also, by backfeeding from the regulator (depending on how it behaves). This is what @jonathanA and I meant by shoving mains back down the regulator.

blackrose · May 4

16 hours ago, wakey_wake said:

The purchase price. Possibly power dissipation? Some are shown with a comedy pogo-like heatsink.

Both will have some 'on' resistance, but I don't if it will be significant under 4A(avg).

Ok, I think I paid about £6 for that SSR. It's not going to break the bank.

16 hours ago, wakey_wake said:

⚠️ the regulator definitely will be live, by back-feeding from the live immersion element. The SSR maybe also, by backfeeding from the regulator (depending on how it behaves). This is what @jonathanA and I meant by shoving mains back down the regulator.

Ah I see, yes. Mistake in my diagram. So the rotary changeover switch should be at the junction where both feeds meet the immersion heater. Got it, thanks.

Edited May 4 by blackrose

wakey_wake · May 4

3 hours ago, blackrose said:

Ok, I think I paid about £6 for that SSR. It's not going to break the bank.

I don't think there is any reason to change what you have. I was only saying there are reasons for/against either.

ETA: but the reason of price turns out to be incorrect.

3 hours ago, blackrose said:

So the rotary changeover switch should be at the junction where both feeds meet the immersion heater.

It's another option. This is why I was asking what effect you wanted.

A third option is putting the regulator after the DPDT, but keeping the SSR before it.

In each case, you must assume that all parts are or could be live unless you've isolated them.

Edited May 4 by wakey_wake
ETA

blackrose · May 4

7 hours ago, wakey_wake said:

I don't think there is any reason to change what you have. I was only saying there are reasons for/against either.

ETA: but the reason of price turns out to be incorrect.

It's another option. This is why I was asking what effect you wanted.

A third option is putting the regulator after the DPDT, but keeping the SSR before it.

In each case, you must assume that all parts are or could be live unless you've isolated them.

Having the bypass side of the system is obviously complicating things. It seems either it backfeeds or means both sides of the system are live. Perhaps I need a 4 pole changeover but again it's getting too complicated.

If I did away with the bypass side of the system to simplify it, what would happen if I plugged in a generator and ran it through the SSR? Would I just switch the relay on the MPPT "always off" to make the SSR permanently conduct mains or would I switch it to manual control "relay closed"?

Presumably the SSR can't somehow backfeed to the MPPT?

Edited May 4 by blackrose

wakey_wake · May 4

(I'm starting to wonder if I'm bringing confusion you didn't need... sorry. But I know you're a bright chap 😁)

1 hour ago, blackrose said:

Having the bypass side of the system is obviously complicating things.

Yes, but it seems a necessary complication unless you put equivalent function on the DC side.

There will be times you want water heated, but the MPPT doesn't see spare energy.

I think reconfiguring the MPPT to make it close the relay, just for that occasion, could be a worse workaround?

1 hour ago, blackrose said:

It seems either it backfeeds or means both sides of the system are live. Perhaps I need a 4 pole changeover but again it's getting too complicated.

I don't see a problem with all mains parts being live. They'll be in a box and you use the isolating switch before opening the lid.

From your diagram 3rd May 10:45, I mainly wanted to be sure you weren't going to stick a finger in the regulator thinking you'd sent the power the other way; and two of us were unsure if the regulator would mind being back-fed with power on its load output.

You might wonder if the regulator will draw an idle power? No. It may have a tiny power overhead, but the regulator only gets power when the heater should have power.

Will the SSR have an idle power? I suspect not, but again it should be tiny.

1 hour ago, blackrose said:

If I did away with the bypass side of the system to simplify it, what would happen if I plugged in a generator and ran it through the SSR? Would I just switch the relay on the MPPT "always off" to make the SSR permanently conduct mains or would I switch it to manual control "relay closed"?

Without a diagram, I don't think I understand that.

From the perspective of the SSR, regulator and immersion heater: whether the mains comes from the inverter, the generator or a shoreline is unknown and irrelevant. They expect 230V 50Hz and will cope with anything moderately close to that.

From the perspective of the MPPT's relay control logic, I've no idea and I recommend the fine manual. 😎

This is why I suggested the experiment with a 12VLED strip or other small lamp.

Also you might leave that in place, else it will not be obvious whether the immersion is doing anything unless you can hear it quietly singing, or watch the inverter load.

If it's sufficiently convenient for you to ask the MPPT to close the relay, you can use that instead of the DPDT.

Or on the DC side, it is safe and easy for all manner of options: toggle switch, raspberry pi, Cerbo GX thingie,

and again you don't need the DPDT.

(Top diode is redundant but reassuring. They're ~£1 / 20.

The GPIO voltage may be slightly too low, might need a transistor. It's simple and safe stuff.)

1 hour ago, blackrose said:

Presumably the SSR can't somehow backfeed to the MPPT?

I would expect excellent isolation from the mains side to the 12V input. The datasheet 😇 will tell you exactly how good.

blackrose · May 4

1 hour ago, wakey_wake said:

Without a diagram, I don't think I understand that.

This is what I'm thinking. System using the MPPT relay, SSR and AC regulator without the previous bypass side so no changeover switch required.

I'm just wondering how it would work if I ran the boat AC system from a generator?

Edited May 4 by blackrose

wakey_wake · May 4

31 minutes ago, blackrose said:

This is what I'm thinking.

You've still got 2x 3-core going into the regulator. Maybe you've tried some and it fits?

31 minutes ago, blackrose said:

System using the MPPT relay, SSR and AC regulator without the previous bypass side so no changeover switch required.

I'm just wondering how it would work if I ran the boat AC system from a generator?

When the AC comes from a generator, the SSR/regulator/immersion don't care, but the MPPT behaviour matters.

Will it close the relay when the mains battery chargers are done refilling the bank?

Can you tell it to close the relay when external mains is detected?

Can you tell it to open the relay when mains load exceeds 2kW?

You have all the right pieces. To find out how the MPPT relay behaves, RTFM or do some experiments, or maybe someone else has one and can advise.

blackrose · May 5

10 hours ago, wakey_wake said:

You've still got 2x 3-core going into the regulator. Maybe you've tried some and it fits?

Well the regulator will need an AC feed in and a load feed out, so whatever I draw in my diagram is largely irrelevant, it won't work without 3 core going in & out. I might fit another gland.

Edited May 5 by blackrose

wakey_wake · May 5

7 hours ago, blackrose said:

Well the regulator will need an AC feed in and a load feed out,

True, but the design suggests they are in one cable which splits elsewhere.

7 hours ago, blackrose said:

so whatever I draw in my diagram is largely irrelevant, it won't work without 3 core going in & out.

I was imagining something like this. The diagram is really helpful - I chewed up several envelopes before reaching this version. 😅

The ELNNL is a chocolate block (screw terminals) in the same order as the regulator. Big dotted box is some plastic container, and cable restraints are implied (ie. I forgot to draw them).

Some folks will say you should never put two wires in one screw terminal or crimp, and there is fair justification to this. Options I'm aware of,

Wago make 3-way joiners, which I believe come in suitably rated versions
Use crimped ferrules on the wires which one might otherwise leave bare, and use double entry ferrules as designed for the double-holed Earth.
New tools, new supplies, https://www.ebay.co.uk/itm/353485780836
Use a 3-entry all-metal earth screw terminal block. Extra mounting to be done.

I don't know what a proper electrician with modern training would advise here. I may be leading you astray.

If you have a crimper and forks, they're good for the SSR.

You might have a separate chocblock for the 12V stuff to make that neater, on a similar scheme.

7 hours ago, blackrose said:

I might fit another gland.

It is another valid option. I suspect "chocblock elsewhere" is easier and neater.

MtB · May 5

3 hours ago, wakey_wake said:

Big dotted box is some plastic container, and cable restraints are implied (ie. I forgot to draw them).

The box stuff goes in can sometimes turn out to be most of the work. Or most of the expense.

Over in "The Combustion Chamber" (forum for gas engineers) considerable derision gets heaped on "Tupperware box" wiring centres. Tupperware sandwich boxes initially seem like a Good Idea for this but actually aren't once you think about it properly. Cable restraints and resistance to water penetration once you start trying to fix stuff down inside one, seem to be the main problems IIRC. The physical strength of the box for cable restraint is important. Nor do you want to be drilling holes through it to screw stuff down as water gets in past your bodgy seals....

jonathanA · May 6

These days there is no need to bodge a tupperware enclosure. Plenty of options from screwfix and toolststion with knockouts for cable entry, depending on what size you need.

If it was me I'd put it all in one box and run singles between the component parts. Cable glands for the cables in/out.

Add a few neon indicators in the lid to show what's going on and bob is your aunts live in lover...

Edited May 6 by jonathanA
Add neons

wakey_wake · May 6

53 minutes ago, jonathanA said:

If it was me I'd put it all in one box and run singles between the component parts.

Also a good option if it the user likes it that way, but the regulator has a control knob and that complicates mounting.

There may also be heat issues, but the kit is hugely over-rated for the load so that might be fine.

What's your opinion on twin wires into fork crimps, wrap-around screw terminals and chocblock screw terminals?

jonathanA · May 6

7 hours ago, wakey_wake said:

Also a good option if it the user likes it that way, but the regulator has a control knob and that complicates mounting.

There may also be heat issues, but the kit is hugely over-rated for the load so that might be fine.

What's your opinion on twin wires into fork crimps, wrap-around screw terminals and chocblock screw terminals?

Well I wouldn't be using a regulator at all but blackrose wont be in every 5 minutes he tells us, so not sure access to the twiddly pot is a big issue.

I try to avoid choc blocks they are the spawn of the devil. On a boat id only ever use them with a ferrule or pin crimp. Conventional wisdom Says fork crimps should not be used under screw terminals, rings should be used as if the screw loosens the ring crimp doesn't fall out. Personally I do use them in some situations but it's a judgement call . I'm sure someone will be able to quote the iso doc.....

Wrap around screw terminals ? Gosh used to use those 40 years ago but even then not often. Only suitable for burglar alarm wiring....

MtB · May 6

4 minutes ago, jonathanA said:

Conventional wisdom Says fork crimps should not be used under screw terminals, rings should be used as if the screw loosens the ring crimp doesn't fall out. Personally I do use them in some situations but it's a judgement call . I'm sure someone will be able to quote the iso doc.....

Shhhhh..... SHHHHHH!!!!!!!

Next thing we'll know is a new rule in the BSS if some BSS chair polisher reads this.

Fork terminations will be banned and virtually every boat on the system will be a BSS fail, so dangerous they are.

wakey_wake · May 6

52 minutes ago, MtB said:

Next thing we'll know is a new rule in the BSS if some BSS chair polisher reads this.

My boat is choc full of chocblocks, but all the chocolate has mysteriously disappeared.

1 hour ago, jonathanA said:

I try to avoid choc blocks they are the spawn of the devil. [...]

Thank you, they are fair points and I will take note as I'm refreshing things. I do like rings for security but some terminals won't take them.

1 hour ago, jonathanA said:

Wrap around screw terminals ? Gosh used to use those 40 years ago but even then not often. Only suitable for burglar alarm wiring....

Or low current 12V signals into an SSR.

I was asking about twin wires into one terminal because Blackrose needs a 3-way for the earths,

On 05/05/2026 at 18:31, wakey_wake said:

Some folks will say you should never put two wires in one screw terminal or crimp, and there is fair justification to this. Options I'm aware of,

Wago make 3-way joiners, which I believe come in suitably rated versions

Use crimped ferrules on the wires which one might otherwise leave bare, and use double entry ferrules as designed for the double-holed Earth.
New tools, new supplies, https://www.ebay.co.uk/itm/353485780836

Use a 3-entry all-metal earth screw terminal block. Extra mounting to be done.

jonathanA · May 7

10 hours ago, wakey_wake said:

Or low current 12V signals into an SSR.

They aren't "wrap around" terminals on the picture I looked at.

10 hours ago, wakey_wake said:

I was asking about twin wires into one terminal because Blackrose needs a 3-way for the earths,

I'm sure blackrose will do something he is happy with. If he takes up my suggestion and puts it all in a single enclosure he won't need to connect 3 earth wires.

Gybe Ho · May 7

On 25/04/2026 at 13:45, IanD said:

You need to connect 12V to the common terminal of the MPPT relay.

I find a brain plus a manual 240v immersion switch works quiet well.

IanD · May 7

40 minutes ago, jonathanA said:

They aren't "wrap around" terminals on the picture I looked at.

I'm sure blackrose will do something he is happy with. If he takes up my suggestion and puts it all in a single enclosure he won't need to connect 3 earth wires.

The Wago-style (lever) terminals are cheap and easily available, include 3-way "joiners", and are a lot better than choc blocks.

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