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invertek charger solar input


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Hi All,

 

I added around 500w of solar to the roof at the beginning of the year, and though it seems to be working just fine I have a couple of ideas that may improve things.

 

Firstly is the connection of the MPPT into the batteries.

 

i have a fairly cheap 40a mppt, standard amazon chinese job, it seems to work well in isolation, however when i start the generator (no shore power) to charge via my 1500w Invertek inverter/charger (stirling rebranded) the mppt display shows a huge reduction in charge current, I'm guessing because the control circuits in the mppt see the terminal voltage as quite high as it is being artificially boosted by the charge voltage from the inverter and believe the batteries to be "full" and thus reduce the solar current?

 

I'm looking at reconfiguring the system to take the most advanting of the solar and have a couple of direct questions!!

 

Firstly, My Invertek inverter does have provision for solar input, it lists several compatible MPPT's which unsurprisingly are all Invertek branded and stupidly expensive. Is it necessary to specifically use an invertek mppt, is there any data communication between the inverter and the mppt which would make it brand unique? If it is compatible, would it be a better place to connect it than directly to the battery terminals in parallel to the inverters connection.

 

Secondly, there are three pairs of terminals on the MPPT, obviously panel input and battery output, the other pair are marked "load" I have left this disconnected as most of my pre-distribution cable is 95mm2 and the terminal struggles with 6mm2 Do I need to find a "dummy load" or something to connect to this?

 

Thirdly, can the assembled think of a better way of doing all of it???

 

Thanks in advance,

 

Bex 

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First it is VITAL that you grasp that after the first half hour or so of charging it is the BATTERIES that control the charging current they will accept (at any given voltage).

 

Before that half hour or so is up the batteries are asking for more current than the charge source can supply so two things happen. The charge source runs at maximum output and the charging voltage is depressed. The voltage gradually climbs to the source's regulated voltage as the batteries charge and the current thy demand drops.

 

If you are charging from two charge sources then during that first half hour or so the batteries will demand so much current that both sources will supply the maximum they can but eventually the charging voltage from both will rise until one or the other reached its regulated voltage. Then, at that point if one charge source is set slightly higher teh lower one will appear to shut down.

 

It won't actually shut down and if you turned on a heavy electrical load it would start providing charge again until you turned the load off.

 

By an hour ago on this nice bright day (in the south) there is every chance your solar controller has decided it should be in float mode. That means it has reduced its charging voltage to prevent it damaging the batteries so it is probably regulating at about 13.8 volts. Upon start up the charger/inverter probably sets itself to a regulated voltage of around 14.4 volts while it decides what it needs to do. (Very soon I would expect that also to go into a float voltage at which point the MPPT might or might not display a higher charge).

 

Now the charger at 14.4 volts will basically do all the charging because at 14.4 volts the solar can not push any current into the system with only 13.8 volts. This is normal.

 

I do not think you have doe anything wrong, the system is behaving exactly as I would expect. You probably have very well charged domestic batteries that will only accept a low charging current.

 

You do not need to do anything. Try it whilst getting light tomorrow and the situation may reverse itself. All perfectly normal.

 

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In answer to your question about the load terminals on your MPPT, the short answer is to ignore them.

The long answer is that the original design idea for these chargers was to use them on solar street lights, so the batteries would charge by day, and then when it got dark (panel voltage is v low) it would automatically switch on the light (load).  You can probably program how long the light should be on for as well.  So unless you really want a light that comes on when it gets dark, ignore the load output.

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Perhaps it is easier to say that whichever charge source be it alternator, inverter/charger or solar that has the higher voltage at any one time will do the majority of the charging (after the first half hour or so).

 

I have heard that some suggest that the load terminals can be sued to charge the engine battery but I am far from sure about that. I am with Chewbacka, ignore them.

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Hi Tony,

Still here, and offering advice, you helped me a very lot during the initial build, though I VERY much doubt you would recognise me!

 

Our domestic usage is huge, I live aboard but make no concession the fact my home is a boat and run a 46" tv, and a valve amp on my hifi, my electrical draw is huge.

 

On a good sunny day my solar is great, but does not provide a full charge so i use the genny. unfortunately I tend to have to start this when I leave for work, as it is rather late when I get back.

 

Ideally I would like the batteries to make as much use of the solar as possible, rather than the mppt going into float, which lead to the question about the inverter being a better option for charge management, with the mppt connected to that.

 

thanks again, Bex

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As far as the Invertek Inverter goes and needing a specific Invertek MPPT....this will probably depend on what the connection is between the 2 units.

If there is/are electronic signal cables (plugin data cables etc), then you will probably need to buy one. If the connections are purely positive and negative cables, then chances are you can use your present unit as it's only an electrical connection, not an information link.

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But does connecting the solar charging cables to the inverter/charger solar input do anything more than just connecting them internally directly to the battery connections? Perhaps a neater solution from a wiring point of view, but functionally no different from what the OP has already done?

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29 minutes ago, David Mack said:

But does connecting the solar charging cables to the inverter/charger solar input do anything more than just connecting them internally directly to the battery connections? Perhaps a neater solution from a wiring point of view, but functionally no different from what the OP has already done?

Exactly this. 

3 hours ago, Tash and Bex said:

Ideally I would like the batteries to make as much use of the solar as possible

So put the initial charge in with the Genny/charger in the morning and then leave the solar to slowly finish the charge through the day. 

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1 hour ago, WotEver said:

So put the initial charge in with the Genny/charger in the morning and then leave the solar to slowly finish the charge through the day. 

That is the way to do it. During that initial half hour or so I talked about and it may be longer if you are a heavy electricity user, the batteries will take everything the charger and solar can throw at it because the heavy current draw will pull both sources voltages down to below regulated level so you maximise the output of both. after the charging voltage has hit (say) 14.2 to 14.3 it means the   batteries are demanding less charge so turn the charger off and leave the MPPT to finish the job.

 

There is one further consideration in that chargers and solar controllers that drop into to a float voltage in all likelihood do it too early so the general advice is that when the source drops into float is turn that source off for a minute or so and then back on (if there is no switch between the panel;s and MPPT just cover the panels for a short while. Then whatever the source is (apart from a standard alternator) the charging voltage will jump back up for a while. I think that I were in the OPs situation I would experiment with setting the float voltage on the charger and the MPPT to 14.4 volts so it never actually dorps into float but if the  charger as to be left on 24/7 it would be vital to set it back to 13.6 to 13.8 volts. Otherwise you will damage the batteries.

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Tha

15 hours ago, WotEver said:

Exactly this. 

So put the initial charge in with the Genny/charger in the morning and then leave the solar to slowly finish the charge through the day. 

Issue being I often leave the boat at 6am, and don't return until 7pm!

 

Perhaps it is time to invest in an autostart marine genny (gulp)

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3 hours ago, Tash and Bex said:

Tha

Issue being I often leave the boat at 6am, and don't return until 7pm!

 

Perhaps it is time to invest in an autostart marine genny (gulp)

Sorry but this is going to appear very hard and heartless.

 

Or take a hard look at the electrical equipment and decide which are vital and which are not much more than nice to have. That may get the demand low enough to do a good long once or twice a week charge and let solar do the rest as best it can.

 

A 46" TV and valve amplifier are far from essentials and I bet you have more like that.  All would be perfectly doable if you have a shore line but you seem not to so you must make adjustments to your lifestyle to accommodate what is possible rather than try to generate enough electricity in winter to live as you want to because given your restraints that is going to be almost impossible. I would be very wary of a generator that may run while you are away from the boat for many hours.

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Agree with the above, there are constant tales of people trying to live in a floating house without shore power that always ends the same way - knackered batteries.

 

Possibly lithium batteries need looking at as they charge much faster than lead acid, so you may get enough into them in your hour or so in the evening and they are far more tolerant of undercharging.  But they are expensive, and the more power you want to use in a day, the more of them you will need.  So you do need to consider power usage.

Edited by Chewbacka
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56 minutes ago, Tony Brooks said:

Sorry but this is going to appear very hard and heartless.

 

Or take a hard look at the electrical equipment and decide which are vital and which are not much more than nice to have. That may get the demand low enough to do a good long once or twice a week charge and let solar do the rest as best it can.

 

A 46" TV and valve amplifier are far from essentials and I bet you have more like that.  All would be perfectly doable if you have a shore line but you seem not to so you must make adjustments to your lifestyle to accommodate what is possible rather than try to generate enough electricity in winter to live as you want to because given your restraints that is going to be almost impossible. I would be very wary of a generator that may run while you are away from the boat for many hours.

Tony, I appreciate your heartlessness however I will not make concession to the fact that I live afloat when it comes to living, and whilst you are correct, if I light purely with candles and spend my evenings reading a book in silence then I could make considerable energy savings.

 

I would prefer to use technology to solve my problem rather than run away from it, to which end 600ah of batteries, 500w of solar and a small suitcase generator do the job. I replace the flooded cells annually and all is well.

 

I will shortly be fitting a full size domestic washer/drier...that's likely to need a decent generator anyway, I could of course get a dolly tub and mangle!!

 

Thank god I didn't mention my tropical fish tank....!

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It sounds to me as if you are a prime candidate for a properly cocooned permanently installed marine generator that hopefully you can run outside the 8 till 8 time slot without annoying other boaters. Then, as long as its powerful enough you would never need to worry about charging again. However I would not want it to run when no one is attending the boat. This will not be a cheap option, probably costing over £10,000 professionally installed but will meet your electricity needs. This will not preclude changing to lithium batteries at some point in the future.

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Exactly Tony,

 

The only difference to your suggestion is that I wouldn't have it professionally installed and that I would buy a second hand unit. 

They are designed to run constantly even when unattended and I would have little compunction doing so ergo I would not need to run it outside of the 8-8 guidance hours.

 

Lithium is certainly an option, I have been investigating the 48v home battery solutions that are appearing to market as well as an electric drive alternative to my diesel propulsion

 

 

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