Running hot water heater from batteries

@ Crisjones
Bloody hell Chris we was just talking about you and Sue less then a min ago ,
Hope all well with you both over there , bet you glad you cross when you did .
Thanks for the info I was a bit worryed about the voltage getting to low .
Last test I did was after 20 mins 11.8v used 24Ah that the voltages under load , turning off the load and the panels the voltage recovered to 12.5v in about a min . That's with the fridge cutting in and out so there was still a small load on .
I started to wonder if there not a answer to the question . Regarding how low the voltage is safe to drop with a heavy load on .
 
sailaboutvic said:
Your calculations of my bank is correct , ofcourse I haven't any intention of running it for 3 hours or anything like that . But 45 mins early in the day would be good leaving enough day light to being the batteries back up to float again .
100Ah for 45 mins that about 75A well about the 50% ,
MY concern is the voltage , will the voltage at this point be at a point where it may damage the batteries.
I only tested this for 17 MINS , voltage then drop to 11.8 v but recovered to 12.5 v very quickly , the recovery time was with the panels turned off ,

This is Why I keep asking what the safe reading of voltage under a load of 100A I can go down too.
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The voltage is almost immaterial, as long as you don't discharge the batteries by more than 50%. 100A for 45 minutes will take about 110Ah out of the batteries, well within the 50% limit (the 110Ah is more than you would think, because of the Peukert effect).
 
pvb said:
The voltage is almost immaterial, as long as you don't discharge the batteries by more than 50%. 100A for 45 minutes will take about 110Ah out of the batteries, well within the 50% limit (the 110Ah is more than you would think, because of the Peukert effect).
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Thanks it was the voltages I was worried about.
Seen by what Chris and you and others have said , I be ok to run it for half hour once the batteries have reach float which will give me plenty of time for the batteries to recover and charge back to float before the end of the daily charging period
 
RupertW said:
My plan is a 110v invertor wired just to the immersion with a VSR so that will send a quarter of the watts to the immersion heater and cut off the batteries at 12.5v under load. and only switch itself on at 13.8v. I accept the invertor loss but it makes use much simpler and means I won’t have to mind it. My main need is finding a cheap 110v invertor with the tiniest current draw when not under load.
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We have a cheap 110v inverter doing just that. We have 720w of solar on the domestiv batteries. The immersion heater is 1200w at 220v. Running on the 110v inverter the immersion heater uses 300w. I use a 1 hour timer to run the 110v inverter with a changeover switch to interupt the 220v circuit to the immersion heater. 1hr on the 300w imersion heater is enough for two showers. Another hour and it will do all the washing up as well. Once the batteries are charged in the morning the inverter is turned on and the water is heated whist the batteries stay on float as long as the sun shines
 
As mentioned earlier in the thread, surely your solar panel controller has a 'dump' terminal for fridges, water heaters etc? Just wire said cheap inverter into this and bob's your uncle with far less risk to the batteries?
Once the water is hot it will (mostly) stop drawing current and your batteries will be properly charged.
Otherwise you have to rely on timers, or worse remembering, to switch the system over.

It does [edit: Can. I was thinking of the old LR44 relay] mean that heating water gets priority over charging batteries, but if they were really flat you could switch off the inverter.
 
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Sailing ABC did a widget that takes excess solar and puts it into a 12v heater element. Wasn't cheap at about £500 but worth watching on You Tube.
 
Have you asked the battery maker? The data sheet gives 100 minutes capacity at 100A, a few years since I played with battery storage but I think that is 100% discharge. 50% would be a conservative limit for deep cycle, I would think 3/4 hour wouldn't be an issue.
 
gordmac said:
Have you asked the battery maker? The data sheet gives 100 minutes capacity at 100A, a few years since I played with battery storage but I think that is 100% discharge. 50% would be a conservative limit for deep cycle, I would think 3/4 hour wouldn't be an issue.
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Remember that the OP has 4 batteries in series/parallel, so each battery is only getting 50A discharge.
 
gordmac said:
Have you asked the battery maker? The data sheet gives 100 minutes capacity at 100A, a few years since I played with battery storage but I think that is 100% discharge. 50% would be a conservative limit for deep cycle, I would think 3/4 hour wouldn't be an issue.
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Posting up above , I only taken 24ah from a 480 bank in 20 mins under that load , not really much .
 
Iliade said:
As mentioned earlier in the thread, surely your solar panel controller has a 'dump' terminal for fridges, water heaters etc? Just wire said cheap inverter into this and bob's your uncle with far less risk to the batteries?
Once the water is hot it will (mostly) stop drawing current and your batteries will be properly charged.
Otherwise you have to rely on timers, or worse remembering, to switch the system over.

It does [edit: Can. I was thinking of the old LR44 relay] mean that heating water gets priority over charging batteries, but if they were really flat you could switch off the inverter.
Click to expand...
If I tryed to run my 3k gen to heat my water heater off the MPPT dumper I think I have quite a big problem . :)
 
Iliade said:
As mentioned earlier in the thread, surely your solar panel controller has a 'dump' terminal for fridges, water heaters etc? Just wire said cheap inverter into this and bob's your uncle with far less risk to the batteries?
Once the water is hot it will (mostly) stop drawing current and your batteries will be properly charged.
Otherwise you have to rely on timers, or worse remembering, to switch the system over.

It does [edit: Can. I was thinking of the old LR44 relay] mean that heating water gets priority over charging batteries, but if they were really flat you could switch off the inverter.
Click to expand...

How do you imagine he'll be able to draw 100a from the solar controller ?

Given that there's dome doubt as to how well 4xTrojan T105s will cope, i imagine it might not work.
 
Vic: "If I tryed to run my 3k gen to heat my water heater off the MPPT dumper I think I have quite a big problem . :)"
Que? I thought we were talking about your solar panel system?

Paul: Of course it won't supply 100A from the solar controller, but it could supply up to near the max the solar panels can output. It is a heating element that is being powered - it will generate heat when supplied with electricity. Nothing like the rated heat output that would be achieved when connected to a mains supply, but heat nonetheless.

E.g. I have similar to one of these on my portable panels: https://www.photonicuniverse.com/up...0512EU_PU1012EU_PU1024EU_user_manual_v1.5.pdf

Ideally add a 12v heating element to shed the heat inside the calorifier rather than from the inverter as per Sailing ABC mentioned above.
 
Yes with LiFePo4 this is relatively easy - I ditched my AGM's and with 2,000AH things are a great deal more straightforward. There is no issue running it through the inverter. I also put in the new Eber Hydronic - which for lots of reasons was an epic, but is probably the best way of producing all the hot water you will need at the touch of the button - albeit not quite so enviromentally friendly. Anywhere there isnt sufficient sun for solar I recommend this as probably the best option if you want to operate off grid, and not rely on the Genset at all to produce power. With a 1,000W of solar and the Hydronic even in winter I can run totally off grid, and only need to run the Genset for very high power items when the solar cant keep up (washing machine) and then the batteries have the huge benefit of sucking up all the excess power as quickly as it can be produced.
 
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