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Author Topic: off-grid dump load query  (Read 10082 times)
AlanM
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« on: June 13, 2012, 10:00:01 PM »

I have finally got my system together and working. 4kW pv feeding through samil grid tie into house consumer unit. Victron multiplus is providing grid to allow gti to work. House loads take first bite at power and then the victron takes any excess and charges 980ah forklift pack. Normally when the battery is full the victron will frequency shift which knocks out the gti, but that is a bit of a waste of potential power. ( and fits)
Any suggestions to create something clever which can switch on a dump load when the battery is full, and as i am off grid, i dont wish to hear of the waste of electricity to heat water, dont have the option to export.
Have enquired with smartgauge about their battery monitor programmable relay but as of now, they have not brought a 48v version into production although they did suggest it was in the process, but no timescale given.

Alan
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billi
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« Reply #1 on: June 14, 2012, 09:11:02 AM »

Alan ,

Do  you use  the Victron s relay  already ?  It can be programmed  to turn on  extra AC consumers , when voltage rises  before the GTI  is switched off

The problem i see with the Victron  AC coupling idea is , that a proper  Battery charging  idea  seems not really possible .  But perhaps i am wrong

I guess  the optimal would be to add a Dump load controller like the Morningstar  Tristar    to grant a better charging idea .....  , but still use the Victrons relay to  try to consume nearly all power first on the AC side

Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
clivejo
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« Reply #2 on: June 14, 2012, 11:23:01 AM »

I have finally got my system together and working. 4kW pv feeding through samil grid tie into house consumer unit. Victron multiplus is providing grid to allow gti to work. House loads take first bite at power and then the victron takes any excess and charges 980ah forklift pack.

How does the Victron know what is excess power?  Do you set the charge rate manually? Cant get my head around that at all!

I would assume, as billi suggests, the Victron will have a set of trigger relays which can be set for different battery levels.  I would use these to switch on a series of loads (immersion heaters, an AC unit to keep you cool in the hot summer months!)

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DISCLAIMER : Iím not responsible for anythingÖ for anything I say or do. Cos Iím a proud member of clan Eejit who once ruled Ireland.
AlanM
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« Reply #3 on: June 14, 2012, 11:32:16 AM »

How does the victron know? Dunno? Seems like magic! But it works, so best not to question too much!

Yes, the charge rate can be set with VE configure. As far i can tell, it has one programmable relay, but it (the victron) works by taking power in and putting it in the batts when excess, but switch a load on and it immediately supports the load with power from the battery, if needed, and then when load drops out, the excess power than goes into batts.

Thanks billi, will have to figure out how to programme the internal relay to do this, possibly set at just below 100%, that way if the dump fails the victron can still frequency shift to knock out the gti?

Alan
« Last Edit: June 14, 2012, 11:33:52 AM by AlanM » Logged
clivejo
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« Reply #4 on: June 14, 2012, 11:50:04 AM »

How does the victron know? Dunno? Seems like magic! But it works, so best not to question too much!

LOL My mother tried that answer with me many years ago, it only makes me more determine to find out why!

I'm guessing the Victron monitors and adjusts its 'grid' voltage to keep it within the preset range.  When the voltage is getting low it pulls power from the batteries, when too high it charges them.  Was this by design or happy coincidence?

Seems a bit strange to me, all that swapping DC-AC-DC-AC, must be considerable loses at each 'interface'.  Of course I have no idea of your set-up and distances, but is there no way to 'charge' directly from the PV panels?
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AlanM
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« Reply #5 on: June 14, 2012, 12:02:00 PM »

 I suppose it senses the load and assists when needed, but dont know if this is done by voltage sensing. My reason for doing it like this is that my meter is on the gti output, rather than on the victron output. Therefore, metering what i generate, before battery losses, or conversion losses. Means having two inverters but there aren't any dc kWhr meters that are certified, so thats why the ac system, rather than dc and charging directly. It did take me a long time to figure out a system that would work and be eligible within the constraints of the fits regime.

Alan
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clivejo
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« Reply #6 on: June 14, 2012, 12:48:52 PM »

It kind of misses the point of what the Feed In Tariff (FIT) is all about!!  But fair play to you, being free from Electric Companies grip must give a great sense of independence.

How do you fair in the winter months?  Do you have any kind of backup for when there is no sun?
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billi
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« Reply #7 on: June 14, 2012, 02:53:53 PM »

Quote
Thanks billi, will have to figure out how to programme the internal relay to do this, possibly set at just below 100%, that way if the dump fails the victron can still frequency shift to knock out the gti?

yes  , i would say this will work, but it is  a bit guesstimating    the number under 100%   bike


My relays  switches on an AC heater   when absorption Voltage is reached , cause until then one can expect that  Sun power is allowed fully into the battery , and  at that voltage set-point   Amps  into the battery will be reduced , while Voltage stays at that level , in a charge-controller setup ,  but in your case  i think the Victron, just switches the GTI off    Undecided   and back on  (depending on HZ) and this is not propper charging , so to find that  off switching point  is important, that one   knows   when the relays should kick in ... to start more AC consumers

My AC heater has only 1500 watt  and my 4000 watt PV  normaly manages   to fully charge (charge controller) the battery, while heater is on



In your case   , beside the  FIT ,  i would recommend a  Dump Load controller  ,  to charge the battery right and the GTI stays on full blast , so first the Victron is dumping via AC  and then the dump load controller via DC  ( unfortunately this will be normally an (immersion ) heater



Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
clivejo
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« Reply #8 on: June 14, 2012, 02:58:51 PM »

That's a good point billi makes.  Do your batteries ever get up to a decent equalization voltage?  Most need this every now and again to keep them health and firing on all cylinders!
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jonesy
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« Reply #9 on: June 14, 2012, 04:09:57 PM »

Alan,
You should make one of EricW's dump controller see http://www.navitron.org.uk/forum/index.php/topic,16451.60.html (I should get a tenner each time I link this)  - but you need the burst control version.  If you put the CT around the Victron, the dump controller will sense any excess and dump it to whatever eg immersion heater, electric space heater etc. Mine is doing a good job of keeping my grid below 245V.
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1.1kWp PV & SB1700. 7kW log burner.
billi
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« Reply #10 on: June 14, 2012, 07:03:33 PM »

artful ,

can you explain ? .... to deserve this tenner  whistlie

In Alans setup , there will be no excess  , that you can sense , all "excess" goes into the battery or Grid  inverter is shut down !

How do you  manage to sense  here ?


Again   , the off grid inverter  will switch an AC load on and off , depending on PV production,  with its own  relay and in relation to battery conditions ,  and i assume , that a charged battery is more important in an off-grid house  than  watering the garden with hot water  Roll Eyes


@Alan   , do you have a  big enough Victron Model, that can  absorb your max 4 kw PV in case you don't consume direct  ?  Is the internal charger big enough ?  You should really look into this !  Cause  , if the system is not balanced, it could cause troubles   sh*tfan

Best regards Billi
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
AlanM
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« Reply #11 on: June 14, 2012, 07:35:40 PM »

Hi Billi,
the multi is the 5000 with 70amp charger, what sort of dump load controller would you suggest for switching dc loads on? I do wonder how the charging regime works when power is "backfeeding on the "ac-out", rather than on the "ac-in", in terms of absorption, bulk etc

Clivejo, "what is the point of the fits?", i no longer burn diesel for my power, that means less co2, (if you believe all that cr@p anyway), and i don't get any export, I only get the generation part, which is what i'm doing. As for voltages or winter, dont know yet, as system in its first week, but i have a mister Lister in storage to be added in later. 

Artful, thanks will have a look at that link

Alan
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billi
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« Reply #12 on: June 14, 2012, 08:39:15 PM »

it is a 48 Volt setup ...so 70 A charger   sound good ....  i am not sure about  
Quote
I do wonder how the charging regime works when power is "backfeeding on the "ac-out", rather than on the "ac-in", in terms of absorption, bulk etc

I think , there is no proper  charging  at all  , when  PV is ac coupled to the ac out  of the Victron ( but ring their support to find out )


I personally  did test  the settings  , and tuned the internal charger down to 0  and charging volts low   , the settings are more for the AC Input  like a Generator or the Grid  , but when i attached my Waterturbine   AC coupled on the "ac-out" side , the  battery was charged  fine and the charger settings for the "AC-in"are overruled whistlie

sorry picture description is in German  , but you can see on the right side, the internal charger set points  and on the left  you see battery voltage and Amps flowing into the battery   from my AC coupled waterturbine   so 6 A are flowing into the battery ( actually 12 A cause i have 2 Multiplus in parallel )  even the internal charger was set to 0 charging Amps  and Absorbtion voltage limit to 25 Volt , but actual battery voltage  is 29.1 Volt






So this is why, i think there is no absorption charge at all   , only bulk  and then Frequency related  on and off switching of the GTI , that sounds  like horror , but   on the other side  we  want to use every unit we can get , and this is where the dump load controller kicks in  , after the Victrons  internal relay for an AC Dump ....

So i think a Morningstar Tristar 60 A   (48 Volt )   should be sufficient , but you need as well the resistors /immersion elements  whistlie  (i guess ca 200 GBP  (for  48 volt DC ones  and 150 for the Morningstar)

And use  the Victrons internal  AC relay first at say  57 Volt  Battery  with 1-2 kw extra AC load  = Grid tie Inverter stays online full blast , then at say 58 Volt the morningstar kicks in   and  takes the rest  = Grid tie Inverter stays online full blast

So  this seems in my eyes  a good solution of battery maintenance and use all in an off grid "AC-couppled" idea
If something fails ( i do not expect this)   the Frequency shift of the Victron  is still there to switch of the GTI

Regards Billi


* ac.jpg (103.31 KB, 765x524 - viewed 530 times.)
« Last Edit: June 14, 2012, 09:40:15 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
AlanM
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« Reply #13 on: June 14, 2012, 09:04:50 PM »

Hi Billi,

No sign of a pic that you mentioned, was it a link or an attachment ?

I asked my battery supplier for the charging voltage and they said it should be 60v, (traction flat plate in cyclic mode), so can the morningstar trip voltage be set or is it a fixed value?

Your solution seems a sensible solution, thank you!
Will ring Victron and ask about the charging on back-feed

Alan
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billi
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« Reply #14 on: June 14, 2012, 09:23:39 PM »

oh no pic....  i can see it  ,
anyway   here again

and my last post  edited   to see picture


« Last Edit: June 14, 2012, 09:41:28 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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