midnight solar battery monitor

wast · May 2018

Estragon said:

I assume you're talking about batteries to run the fridge (2x24 vs 4x12)? If so, yes, for a couple of reasons. Four batteries in parallel could charge/discharge differently, leading to unequal states of charge. Second, at 24v the DC currents are 1/2 those at 12v. For example, say the fridge draws 600w to start. Ignoring inverter losses, that's 600/12=50a@12v, vs 600/24=25a@24v.

If you already have a good (pure sine wave) 1000w 12v inverter, I'd use it. If you're planning on buying one, 24v may be a better choice. A cheap hardware store square wave inverter may cause heating of the fridge motor and potentially reduce lifespan or possibly not run at all.

2x24 for the batteries was what I was talking about... I don't have an inverter as of yet so if get an inverter then maybe the route to take... this 12 versus 24 versus 48 really boggles this old mind.... oh well if I keep filling up the old noggin something might eventually sink in.. really appreciate you guys patience

BB. · May 2018

Lead acid batteries are all 2 volt cells in series.

I use around 800 ah battery capacity to go next higher voltage. A 10% rate for 800ah is 80 amps. That is roughly the maximum charging current for a high end mppt charge controller.

If you go over 80 amps charging, you either need 2 charger controllers at 12 volts (2x 80 at 12 volts or 1x 80 amp controller at 24 volt)

Reminder power = volts * current

You can either 2x the current or 2x the voltage for 2x more power.

Also, when you get over about 100 amps DC current (charging or loads), the copper cable gets very thick and expensive. And voltage drop becomes a big issue (especially at 12 volts).

Bill

Estragon · May 2018

> @wast said:
>
> 2x24 for the batteries was what I was talking about... I don't have an inverter as of yet so if get an inverter then maybe the route to take... this 12 versus 24 versus 48 really boggles this old mind.... oh well if I keep filling up the old noggin something might eventually sink in.. really appreciate you guys patience

Nothing wrong with taking the time to understand things before pulling the trigger. There are no silly questions, only silly pride preventing the asking of "silly" questions.

wast · May 2018

Estragon said:

> @wast said:
>
> 2x24 for the batteries was what I was talking about... I don't have an inverter as of yet so if get an inverter then maybe the route to take... this 12 versus 24 versus 48 really boggles this old mind.... oh well if I keep filling up the old noggin something might eventually sink in.. really appreciate you guys patience

Nothing wrong with taking the time to understand things before pulling the trigger. There are no silly questions, only silly pride preventing the asking of "silly" questions.

so after some consideration this is what I propose to do.. take my 4 170 ah batteries and make 2x24volt batteries.. for charging I will use the 2x190 in series. a friend has a 3000 watt pure sine wave inverter/ 80 ampcharger that I can get for a reasonable price. .. so if I am reading the info correctly I could probably add a couple more panels to my solar array with the 40 amp mttp charge controller on a 24 volt system.. does this seem like a reasonable way to go and also would a 3000 watt inverter be too much.. this system would only run a refrigerator that will consume roughly .75 kw a day...

Photowhit · May 2018

wast said:

so after some consideration this is what I propose to do.. take my 4 170 ah batteries and make 2x24volt batteries.. for charging I will use the 2x190 in series.

The battery bank of 2 strings of 2 in series, we would normally call 2x2, each battery having 170 amps would end up with a 24 volt 340 ah battery bank.

wast said:

a friend has a 3000 watt pure sine wave inverter/ 80 ampcharger that I can get for a reasonable price. ..

So is the inverter designed to run on 24 volts? Might go ahead and tell us the make and model.

wast said:

.. so if I am reading the info correctly I could probably add a couple more panels to my solar array with the 40 amp mttp charge controller on a 24 volt system..

A 40 amp charge controller should be able to handle about 1200 watts of panels cost effectively, if it can be 'over paneled. You are in the far north so check to see if the VOC will be too high for your controller. It is possible for 1200 watts of panels to procuce 1200 watts and more, but on normal days it will produce about 900 watts.

wast said:

...also would a 3000 watt inverter be too much.. this system would only run a refrigerator that will consume roughly .75 kw a day...

3000 watts is a bit higher than you are able to utilize fully on your system, at least for more than a short period of time. It may work out fine, understanding that you won't be using more than a smaller percentage of the available energy.

The question is how much energy does the inverter use by it's self, and does it have an effective 'sleep' mode.

Most fridges will use more energy than .75 KWh's a day. Is this a newer fridge?

wast · May 2018

Photowhit said:

wast said:

so after some consideration this is what I propose to do.. take my 4 170 ah batteries and make 2x24volt batteries.. for charging I will use the 2x190 in series.

The battery bank of 2 strings of 2 in series, we would normally call 2x2, each battery having 170 amps would end up with a 24 volt 340 ah battery bank.

wast said:

a friend has a 3000 watt pure sine wave inverter/ 80 ampcharger that I can get for a reasonable price. ..

So is the inverter designed to run on 24 volts? Might go ahead and tell us the make and model.

wast said:

.. so if I am reading the info correctly I could probably add a couple more panels to my solar array with the 40 amp mttp charge controller on a 24 volt system..

A 40 amp charge controller should be able to handle about 1200 watts of panels cost effectively, if it can be 'over paneled. You are in the far north so check to see if the VOC will be too high for your controller. It is possible for 1200 watts of panels to procuce 1200 watts and more, but on normal days it will produce about 900 watts.

wast said:

...also would a 3000 watt inverter be too much.. this system would only run a refrigerator that will consume roughly .75 kw a day...

3000 watts is a bit higher than you are able to utilize fully on your system, at least for more than a short period of time. It may work out fine, understanding that you won't be using more than a smaller percentage of the available energy.

The question is how much energy does the inverter use by it's self, and does it have an effective 'sleep' mode.

Most fridges will use more energy than .75 KWh's a day. Is this a newer fridge?

the inverter is xantrax ( not sure if that is correct spelling) and it is 24 volt... the refrigerator is new as a matter of fact haven't received it yet as it is still on order... energy start 296 kwh per year... it is only 10 cu ft.. I will check out inverter to see what it uses before I bite the bullet... if not right for me I will purchase a 1000 as the only thing on this system would be the refrigerator..

Estragon · May 2018

IIRC my 3500w PSW inverter/chargers run ~35w just being on. 35w x 24hrs = 840 watt-hrs - about doubling the 750w (plus inverting losses) to run the fridge.

They have a sleep mode that uses something like 8w, so assuming the fridge is off-cycle for 16 hrs, you could shave ~35-8=27w x 16hrs = 432wh off the tare load. A potential issue could be if the fridge has electronic defrost timers etc. To search, the inverter would pulse every "X" seconds for a load greater that "Y" watts, which may not play well with the fridge electronics. FWIW.

mike95490 · May 2018

for a single fridge, a 1kw PSW inverter seems to be a good balance between starting surge requirement, and low power running. Some 600w and 800w inverters can't quite seem to manage the starting. 3Kw is overkill.

In my opinion.

Saipro · June 2018

True but loads invariably grow with time. If the 3kW inverter has a reasonable idle power consumption (unlikely), go for it. If not, a 1kW with good surge rating should be more than adequate (beware the idle consumption of any inverter).

wast · June 2018

battery monitor seems to be working as it is supposed to be... green light on which means that the system has been charged recently and batteries are 100 % charged...seems like it takes some time for it to digest as the info

midnight solar battery monitor

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