How to charge a Lithium Battery from spare power from a grid tie PV installation.

[JohnU]

How do I charge lithium batteries from spare power from home grid attached PV using a diverter box that heats hot water using an I immersion. I now wish to divert the spare generated power to a lithium battery. Note the diverter box works with immersion heaters as it’s a resistive load.

Hope I have explained this correctly.

I can’t find anybody who have used this concept.

 

[mopat]

Battery charger.

 

[Nevadablue]

How hot does the water get? How would hot water charge a battery except to run some sort of generator by steam?
I am interested in your question, but not sure what it means.

 

[JohnU]

Battery charger.

I’m not sure if a straight battery charger will work when it’s source is a variable voltage AC from a home PV grid tie inverter using spare power. Ideally it needs a charger with a Lithium profile but that would need an intelligent charger. That’s my problem.

 

[JohnU]

How hot does the water get? How would hot water charge a battery except to run some sort of generator by steam?
I am interested in your question, but not sure what it means.

The diverter units ( immersun ) divert power to a resistive load like an Immersion heater to heat hot water in your hot water tank.

I need a charger or solar charger controller to take the variable voltage like a resistive load and charge my lithium battery with excess power I do not use at home from my PV installation.

 

[Nevadablue]

Why is the voltage variable? If you are on the grid, a charger will be fine.
I ordered this one on recommendations from this forum. It should arrive tomorrow. I will be reporting back on how it works.
I’m still confused. You don’t have an inverter?
(the specs on the ‘input voltage’ are obviously a typo)

 

[Bud Martin]

So let me get this correctly, you want to use the variable AC output of the Immersion controller which right now is providing the variable AC to the heater depends on power availability of the PV system, correct?
Page 27
Must be simple resistive load without electronics control.

That means you cannot use the charger connected to the output of this unit.

This is the unit you have, correct?

https://www.immersun.co.uk/wp-content/uploads/2019/11/immersun-installation-and-user-manual.pdf

 

[JohnU]

That’s my Immersun. In the UK we get paid for all the power we produce from our grid tie PV installation. This type of device allows all power to be used when I produce more than the property is using by diverting the variable spare to resistive loads ie immersion heaters or simple electric air heaters.

 

[Bud Martin]

You may be able to use Current sensing switch to detect the current flowing through the heating element and use that to turn on the switch that will supply AC to your battery charger that is connected to your house outlet.
Something similar to this.

https://www.amazon.com/Current-Sensing-Normally-Adjustable-SZC23-NO-AL-CH/dp/B07N1P6TWL/ref=sr_1_3?

There are many of them.

Amazon.com : current sensing relay

 

[JohnU]

Thanks for the idea. The switch would be On or Off when what I would like is the same as my immersion heater it can take a varying power source from the Immersun. The idea is to use as much power from the grid tie PV inverter without using any mains power from the grid.

 

[Bud Martin]

Your home outlets are powered by Grid-tied PV, correct? But you want the battery charger to be variable charging rate based on excess availability PV, correct?

 

[JohnU]

My home outlets are grid tied to my solar PV inverter, on a sunny day I use less grid power as more power comes from my PV inverter. In the UK we get paid on our power we produce not what we give back to the grid. Hence companies like Immersun produce a diveter unit. This measures the amount of power coming off the PV and if it’s more then I am using instead of letting it go to the grid it will allow the margin to a resistive load. In my case this is an immersion that heats my hot water for free. When the water tank gets to a set temperature the immersion will turn off. The immersun can sense this and switch to a secondary output again it has to be a resistive load. Now I wish to have a battery charge or something similar on that output to charge a large lithium battery for free. I hope this explains it?

 

[JohnU]

We have to remember that my immersion could be provided witn 30w to 3000w depending on the difference between what I’m generating and what the property is using. This can be variable all day depending on the sun and property usage.

 

[JohnU]

Why is the voltage variable? If you are on the grid, a charger will be fine.
I ordered this one on recommendations from this forum. It should arrive tomorrow. I will be reporting back on how it works.
I’m still confused. You don’t have an inverter?
(the specs on the ‘input voltage’ are obviously a typo)

View attachment 114690

The voltage the immersun gives to a resistive load like a immersion heater must be variable as it adjust to the surplus power going to the grid to the immersion to about a delta of 60w only going to the grid if it can be diverted elsewhere.

 

[Goboatingnow]

It depends on the minimum and maximum voltages thd system produces. Is it AC or DC that is diverted.

Power supplies with CC control can be got and can operate over a fairly wide range of input ac or dc voltages.

We need more data Mr spok

 

[billt1827]

The voltage the immersun gives to a resistive load like a immersion heater must be variable as it adjust to the surplus power going to the grid to the immersion to about a delta of 60w only going to the grid if it can be diverted elsewhere.

Immersuns and similar diverters are switching devices not analogue ones. If there is excess PV power available they switch the immersion element on and the immersion consumes the full 3kW. However they do this very quickly (within the sampling time of the electricity meter). They are modulating the power by fast switching. They work well with resistive loads, they won't work well with a battery charger.

 

[JohnU]

Immersuns and similar diverters are switching devices not analogue ones. If there is excess PV power available they switch the immersion element on and the immersion consumes the full 3kW. However they do this very quickly (within the sampling time of the electricity meter). They are modulating the power by fast switching. They work well with resistive loads, they won't work well with a battery charger.

Thanks for that update. Do you think there is away I could use this switched power to charge a battery?

 

[billt1827]

You could use something like the system that OpenEVSE use in their EV charge controller. Monitor excess solar generation over use, when that exceeds the threshold necessary to operate the charger drive a relay to switch the charger off. When generation drops below use switch the charger off after a delay - you don't want to switch chargers on and off too quickly.

It should be possible to use a Shelly EM to sense production and drive a Shelly 1 to do the switching if you don't have any other monitoring. (I haven't used a Shelly EM so I can't say for sure that it would work.) However you would still end up using some grid power, it won't be as effective at not importing as an Immersun.