Grid tie and battery together

[jturner777]

From an experienced electronics technician, your relay is fine for your application. I would suggest you perform 2 items to increase the longevity of contacts though.
1) Parallel connect the 2 "gangs" of contacts so that the current is shared between the 2 contacts. Thus you have 80 amps capacity instead of 40 amps. And only 8 amps thru each contact instead of 16 amps thru one contact.
2) Connect a .1 mfd to .5 mfd 50 VDC capacitor across the paralleled contacts. This will greatly reduce the spark when then contacts open or close and increase contact life. Think of your old cars points and capacitor ignition system. Good luck!

[Tired sparky]

Ampster, yes it has islanding protection. I tested this by switching off the mains to inverter fused spur unit and the inverter shuts down. It also has a nifty feature where you put a sensor on the incoming mains Live cable and it knows how much power you are drawing from the mains. It then will only let up to that amount of power into the house mains from the panels!! It’s so you don’t go exporting any extra back into the grid and giving the power company free electricity.

[SunEagle]

Arc flash.jpg

Yep. I have been there and witnessed that type of arc flash. Although it was 480v AC.

I have also seen smaller devices arc on DC voltages or Hi Voltage AC (138kv) in a substation. All of them are pretty but none are safe.

[Ampster]

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The black cable from the bottom of GTI is the 230 volts AC and goes to that small white watt meter then down to the switch fused spur then into the socket and off into the house mains.
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I don;t know what the regulations are in your country, but in the USA it is required to have a safety interlock between the grid and the GT inverter to protect the linemen working on a downed grid. Generally that is part of the the GT inverter. Does your inverter have that safety interlock?. In other words, does your GT inverter shut down when the grid is down? I am just checking my assumption that the use of the term GT inverter implies that it does.

[Ampster]

Thanks, ah yes good idea, it might pay to put a fuse after the main solar panel incoming switch. I was going to get a DC circuit breaker that would both be a switch and a short circuit current breaker but never did, instead using a regular AC 100 Amp domestic distribution board main switch I had to hand.

Those are the kinds of things that worry the risk adverse moderators. It is very important when switching a and protecting DC loads to use devices that are specifically rated for DC. You probably already know this but for the benefit of other readers, switching AC is simple because 50 or 60 times a second the voltage goes to zero. That is never the case with DC and that is why DC switches, relays and circuit breakers have to be designed for the kind of arcs that flow when connecting or disconnecting a large DC load. The large contactors used in EVs are enclosed and include arc suppressing circuitry, inert gasses or both..

[Tired sparky]

Thanks, ah yes good idea, it might pay to put a fuse after the main solar panel incoming switch. I was going to get a DC circuit breaker that would both be a switch and a short circuit current breaker but never did, instead using a regular AC 100 Amp domestic distribution board main switch I had to hand.

[Ampster]

Ampster, are you saying there could be connections within the CC and or GTI that might not like being switched back and forth under a possible maximum load and might throw a wobbly?
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I was actually in the solar shed today (we are under a soft lockdown here) when it switched from battery charge mode to Grid Tie mode with the faint click from the relay! Quite satisfying, I hope it lasts a while!!!

Whatever happens its anothet learning curve and I will update good/bad things that occur.
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I don't know because I am not as familiar with the inner workings of a charge controller. It would not be an issue with my grid tie inverter because it uses optimizers on the panels which drop the voltage and current when disconnected. I was trying to provide some context around the fears of others around the risks of switching DC. One mentioned surge currents and I was just throwing out some examples of where you most likely might see them.
Most relays I have used are enclosed and the voltages and amps you are working with are reasonable. As you mention if you blow through a $15 relay I will be no big deal. The contacts will weld in one position or the other. The likelihood of a short circuit that creates those major spark storms is unlikely assuming you have fuses or circuit breakers in the right places.

[Tired sparky]

Ampster, are you saying there could be connections within the CC and or GTI that might not like being switched back and forth under a possible maximum load and might throw a wobbly?

I understand that in normal use solar CC’s gradually ramp up in power as the Sun rises so might not like sudden inrush current when being switched. Inverters should be ok as they operate as either on or off under a load demand?

I was actually in the solar shed today (we are under a soft lockdown here) when it switched from battery charge mode to Grid Tie mode with the faint click from the relay! Quite satisfying, I hope it lasts a while!!!

Whatever happens its anothet learning curve and I will update good/bad things that occur. Thanks for the good technical input from y’all.

[Tired sparky]

Solar comes in through that red switch. The negatives are commoned behind the panel. The positive goes to the tiny relay left of main switch.

From there it splits with one leg going to the white/grey MPPT CC and the other going to the Blue GT inverter.

The black cable from the bottom of GTI is the 230 volts AC and goes to that small white watt meter then down to the switch fused spur then into the socket and off into the house mains.

The grey/white MPPT CC feeds to the battery bank. There is a display screen in the house linked by a 30 metre (100 foot) Ethernet cable.

The silver box is a 24-12 volt transformer for my low volt circuits which include that black car cigarette socket. It connects to a blade fuse distribution unit on the right.

The round green lit display is a battery monitor.

The black thing under main MPPT and next to main switch is another watt meter.

The silver MPPT CC and yellow/grey display are a separate 12 volt system that will be removed as it’s redundant now I have the 24 volt system.

The grey ‘MPPT’ (PWM) CC at the bottom of the picture is the thing monitoring the battery bank and operating the relay.

Thats probably clear as mud but maybe it will help others see what I’m on about here?

[littleharbor]

Arc flash.jpg

[Tired sparky]

F8463B3C-D090-47D6-962B-005959A2712E.jpeg

[Ampster]

That is helpful information, In this application a double throw relay is needed and I am not aware of any in SSRs in that format. I am familiar with inrush current on the DC battery side switching an Inverter or controller in an EV. I haven't tested it on my hybrid inverter because I always connect the batteries and then use the circuit breaker, I did see an episode of EVTV where they were using a contactor as a low voltage and high voltage cutoff and they did blow the capacitors or Power transistors in a Chinese Inverter.

This issue in this post is about the DC from the panels and the impact on the charge controller or gridtie inverter. I do not know the impact of switching the solar input to a charge controller or inverter. It is the capacitors that cause the surge currents and there very well may be capacitors on that side of those devices and that is what the OP should be aware of. The result will most likely be a welded contact the consequences of which the OP needs to be aware of if it could result in overcharging his batteries. I can't imagine a scenerio with a grid tie inverter where welded contacts on the solar side would be a problem.

[Mike90250]

Yes, pics can be posted. Lowering the res from 12mega pixels to something more reasonable is recommended.

Here's a couple links to relays and failures and prevention
http://www.omron.com.au/service_supp...2182/index.asp

and this sort of outlines the problems too

https://electronics.stackexchange.com/questions/16581/how-do-relay-contacts-survive-inrush-current

Using high voltage Solid State Relays can work, but you need "snubbers" to cut down voltage spikes and surges which will fry SSR's

[Tired sparky]

No haven’t, I only work with 230/415 V AC. You get some pretty good arcs and bangs if you mess up tho, I have dozens of side cutters over the years that will attest to that lol.

[SunEagle]

I’m hoping these sort of components have s bit of wiggle room on their specifications? Most things in the electrical industry are for safety.

You are right but if you have never seen a DC arc flash you are missing out on a O **** event.