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This may be a silly question, but I have an Apollo Gem installed


to use spare power from my solar panels to heat the hot water, via the immersion and this works well.

The unit can however support two outputs, in what they describe as variable or threshold modes as described on pages 21-24 and page 47.

Variable is documented as being for pure resistive loads, whereas threshold is for most other things and to use this you define the power the load requires and the Gem only enables it when this is available.

Now I assume I can definitely use threshold mode, with the output running to a dedicated single single gang socked in the garage, to charge a car with the threshold set to say 2.5Kw. However with only a 4Kw supply the amount of time this much power is available will be limited.

Now specialist chargers like Zappi can happily send less that 3Kw to the car, if this is all that is available. As such the car can handle this.

Would the electronics in the 3-pin PHEV charging cable be able to handle being connected to the variable output, as it will get the expected 240v, but the power delivered will obviously vary depending on what is free? Or would this simply not work, or worse possibly cause damage?

Thanks
 

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This may be a silly question, but I have an Apollo Gem installed


to use spare power from my solar panels to heat the hot water, via the immersion and this works well.

The unit can however support two outputs, in what they describe as variable or threshold modes as described on pages 21-24 and page 47.

Variable is documented as being for pure resistive loads, whereas threshold is for most other things and to use this you define the power the load requires and the Gem only enables it when this is available.

Now I assume I can definitely use threshold mode, with the output running to a dedicated single single gang socked in the garage, to charge a car with the threshold set to say 2.5Kw. However with only a 4Kw supply the amount of time this much power is available will be limited.

Now specialist chargers like Zappi can happily send less that 3Kw to the car, if this is all that is available. As such the car can handle this.

Would the electronics in the 3-pin PHEV charging cable be able to handle being connected to the variable output, as it will get the expected 240v, but the power delivered will obviously vary depending on what is free? Or would this simply not work, or worse possibly cause damage?

Thanks
The short answer is definitely not. Resistive means an immersion heater or convector heater.

Edit: However, the threshold setting might work, but the minimum current for charging is 1.6kW. Any less and the charging simply stops.
 

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The long answer is that "threshold" will almost certainly work but only with a fixed EVSE and one that you can vary the advertised output (eg like a Viridian EVSE). You will need to do some fairly simple electronics/wiring/circuit building.
 

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If you have a dumb Rolec EVSE, the ECU ("brains" module) in it will be a fixed 16A or 32A one. But it can be swapped out for the Viridian Mainpine ECU (choose tethered or untethered) and this one lets you set the car's charging current in very fine increments, from 6A (the minimum allowed) upwards. So a rotary multi-position switch + a bank of resistors can be wired up to choose this. But it's not ideal; if you set your threshold to 2.4 kW, the Gem won't charge the car until you do have that much leccy free. Turn the kettle on for a cuppa, that margin suddenly goes, and you'll interrupt the EVs charging with zero notice while it's drawing the 2.4 kW that you'd selected on your EVSE. The EV isn't going to like this. Mine will detect a charging EVSE failure, throw a hissy fit & give me a hard error message on the screen next morning.

You'll also not be charging the car at all while there's between 1.5 kW & 2.4 kW available, which can be a lot of a slightly-overcast summer day. If you try to make more use of this lower level, and set your threshold to 2 kW, you'll capture more of the dull days, but miss out when the clouds suddenly roll back and you could be grabbing 3 kW.

The correct sequence for an EVSE to shutdown a charge is it reduces the charging current from 32A, 16A, whatever, down to 6A over a period of <5 seconds ish. Then, the EVSE removes the "charging electricity available" signal so the car knows to stop charging nicely, and current drops to 0 amps without any nasties. I have no doubt that Zappi does this, but a crudely tweaked EVSE or an EVSE that's suddenly interrupted by timers or GEM-like "smart" switches is not a nice solution.
 

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If you have a dumb Rolec EVSE, the ECU ("brains" module) in it will be a fixed 16A or 32A one. But it can be swapped out for the Viridian Mainpine ECU (choose tethered or untethered) and this one lets you set the car's charging current in very fine increments, from 6A (the minimum allowed) upwards. So a rotary multi-position switch + a bank of resistors can be wired up to choose this. But it's not ideal; if you set your threshold to 2.4 kW, the Gem won't charge the car until you do have that much leccy free. Turn the kettle on for a cuppa, that margin suddenly goes, and you'll interrupt the EVs charging with zero notice while it's drawing the 2.4 kW that you'd selected on your EVSE. The EV isn't going to like this. Mine will detect a charging EVSE failure, throw a hissy fit & give me a hard error message on the screen next morning.

You'll also not be charging the car at all while there's between 1.5 kW & 2.4 kW available, which can be a lot of a slightly-overcast summer day. If you try to make more use of this lower level, and set your threshold to 2 kW, you'll capture more of the dull days, but miss out when the clouds suddenly roll back and you could be grabbing 3 kW.

The correct sequence for an EVSE to shutdown a charge is it reduces the charging current from 32A, 16A, whatever, down to 6A over a period of <5 seconds ish. Then, the EVSE removes the "charging electricity available" signal so the car knows to stop charging nicely, and current drops to 0 amps without any nasties. I have no doubt that Zappi does this, but a crudely tweaked EVSE or an EVSE that's suddenly interrupted by timers or GEM-like "smart" switches is not a nice solution.
Does an EVSE really need to to down the charging current from 32A to 6A over a long period, 5 secs or so ?

If one interrupts a charge manually, it looks to be pretty instantaneous, certainly less than 100ms.

Also wondering if the GEM has multiple output levels?
 

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The J1772 spec allows the car a few secs to respond to changes in info, maybe 3, maybe 5. I can reduce the current on my granny Evse from 16A to 6 instantly, and the square wave signal will change instantly, but it actually takes about 2 to 3 secs for the car to respond. Simply yanking the supply away instaneously while say 32 amps is being drawn is asking for trouble imho. Yes the car will survive it, could happen when there's a power cut but not nice.
 

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On that basis, one could never end a charging session at anything other than 100%.

Sorry just don't buy this piece of folklore.
 

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Evse min charging current is 6A, whether on 120V or 240V. So you get minimum transients/spikes etc when switching on/off at 6A, then ramping up/down. Fwiw my car detects sudden unexpected loss of charging and assumes the Evse broke.
 

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Evse min charging current is 6A, whether on 120V or 240V. So you get minimum transients/spikes etc when switching on/off at 6A, then ramping up/down. Fwiw my car detects sudden unexpected loss of charging and assumes the Evse broke.
Even if the pilot is powered down????

Does the Zappi really power up and down over a period of minutes?

If so, not sure if that is done as per OEMs specs in which case the Zappi must have design approval by Merc, Tesla, BMW, MITSUBISHI, MG, etc.

Interested to see how this is coordinated in practise.
 

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Discussion Starter #10
Many thanks for all of the replies, very helpful.

My level of understanding probably covers DCs, but AC with capacitive/inductive loads get far more complex. As such I was simply thinking of Power = Volts * Amps and so assuming the Gem Variable output is always 240V then the variable power output would simply be the result of the current changing.

On page 5 of the document Gem states

In threshold power mode Apollo GEM uses a programmable threshold to determine when enough surplus power is available from the micro generation system to power a connected appliance. This mode would be used typically to power non-heating appliances that cannot use a variable power supply. Again, priority is always given to the energy demands of other household appliances.


Now I can see most electronics would not handle variable power, but I was hoping that battery charging is an exception as by definition this is allowed as proven by Zappi and others. However unfortunately it seems I am incorrect.
 

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Things like Zappi have to have full mains power coming in, as they vary the power they offer to the car second by second maybe. Solar output can ramp up hugely in a few milliseconds, and the Zappi will see this and suddenly change its offer from maybe 6A up to whatever the solar spare amps are, could be 3.5 kW say 14 Amps on a sunny day with a 4 kW panel setup, lots more if yu have a bigger system obvs. So it will vary the low-voltage square wave-form very quickly indeed. The car will track that, increasing and reducing what it takes to match. The car has about 3 secs to respond, so I'd expect the Zappi to be kind, and take a few seconds (say 5?) at least between changes to what it offers. It's going to be very unhappy if it offers 14A to a car, only for the input to be restricted to say 10A by the GEM! It's also going to have its own low voltage supply to feed its own cpu, and that bit of circuitry also may not like the chopped-up mains waveform that you get with these variable-mains-out things. Only very simple things, like resistive heating elements, incandescent lightbulbs, are suitable for these chopped-up distorted mains waveforms.

Zappi tells the car how much current is available over a low-voltage CP line, and it's up to the car to not exceed that current. If the car does exceed it, the Zappi should detect this as a fault in the car, and shut down the charging process & signal a fault.

Gem in Threshold mode is going to be doing a simple mains-on/off switch, none of that fancy mains chopping stuff.

In variable mode, there are various things it could do to the mains waveform to control the output power. It could let each bit of the voltage sine-curve starting from 0V rise, and as it rises (and maybe starts to fall back towards zero) it could measure the instantaneous current; by summing the incremental bits of power used during this half-cycle (1//50th of a second), it could work out how much power has been used. When the limit is reached, it could turn the sine-wave off instantly for the rest of that half-cycle. This then repeats for the next half cycle of opposite direction current flow, etc.

Or, it could make a very smooth sinewave (to avoid that sharp cut-off which may generate RF noise & interference) which is at some lower voltage than 250V, if its reducing the power below 3 kW. To do this, it would be turning the input 250V sinewave on & off very, very quickly indeed, watching the voltage going up, and when it's above the path of this low-voltage sine wave, switches off for a few microseconds, then on, then off, and with a bit of smoothing in the output circuitry you won't see these switches, maybe just a tiny bit of ripple. If it does this, and you've set a 6A limit and the Zappi is using all of this, you might only be giving Zappi 100V AC! Ugh.
 

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A lot of cross purposes in the above posts.

If you set the threshold power at say 10A, and provide a switched signal to the Viridian controller to advertise to the car to draw 10 A, then the car will draw 10A of surplus solar generated power, actually balanced from the grid.

If the sun intensity increases, and say 18A surplus available, 8 amps would be "wasted".

If the sun intensity dips so that the surplus dropped to say 9 amps, the threshold would switch off and the car would stop charging ( or you could have the Viridian default srt to say 6 A).
 

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Exactly, which is why a purpose-designed solar-aware charger such as Zappi will do a much better job of optimising use of solar leccy. Trying to "roll your own" with a crude on/off threshold switch isn't anything like as good.
 
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