diy solar

diy solar

Have i drained my bank too far?

First off is to gain an understanding of what a battery is. Batteries are a chemical device and not a can of gasoline. A good write up is at: https://climatebiz.com/battery-capacity/

All the well meaning advice on proper charging techniques does not change the basics. Voltage as a indication of capacity is a real loose measurement. Frankly most inverter setups have a ridiculously low voltage cutoff as standard. By the time they cutoff you have already passed where it is good for the batteries chemistry to be at. As a illustration about voltage and capacity is solar panel Voc rating. You can see a high voltage on you panels in dim daylight with no load. However try loading them and the voltage drops like a rock if they are not in full sunlight. Your batteries can show normal voltage also without load. However they lack the chemistry inside to deliver anything.

Rather than waste too much time in the weeds in micromanaging your charging you probably want to look at your loading and solar supply. Suffice to say, if you can avoid putting much use on a battery you are better off.
Yes sure thing, I got caught out that day as I thought there was plenty of charge.
If 10.8V is too low for 50% I might raise it to 11 volts to be safe. But I doubt I will be draining these batteries much in a typical day.
 
I checked on the system today and I discovered I can't extend the boost duration anymore than 3 hours, so just set it to that.
Voltage was still about 29.4V after about 4 or more hours of daylight and still drawing some amps, see screenshot below.
Is this controller going to be suitable if I can only set to 3 hours?
Screenshot_20220802-121712_EPEVER Pair.jpg
 
Your voltage settings for the controller are okay. The 4 hours max boost time is to short.

From your screenshot around noon, I see there’s only 9.1 A going into your battery. That’s not much considering your 540 Ah bank. It would take 270Ah/9.1A=30 hours just to refill 50% charge.

And that’s even without taking the 90% charge efficiency into account.
Plus it doesn’t stay noon for 30 hours.

Is your charging capacity up to its job? Meaning how much are you using on an average day?
 
Your voltage settings for the controller are okay. The 4 hours max boost time is to short.

From your screenshot around noon, I see there’s only 9.1 A going into your battery. That’s not much considering your 540 Ah bank. It would take 270Ah/9.1A=30 hours just to refill 50% charge.

And that’s even without taking the 90% charge efficiency into account.
Plus it doesn’t stay noon for 30 hours.

Is your charging capacity up to its job? Meaning how much are you using on an average day?
I have 1600w worth of panels available feeding this and intend to add my old panels to the system to add almost another 900W of capacity from the old panels.
I have no idea if being winter here that these panels were anywhere near max output or not, but the sun was up.
I can't even extend boost to 4 hours, it maxes out at 180mins.
I flicked on the kettle after taking this screenshot and it jumped up to about 800W coming from the panels according to the app, but it never indicated that it was draining the battery, it still displayed two green arrows in the direction from the panels, this made no sense to me considering that the kettle would be about 2000W.
As far as power usage goes, I don't really have any idea unless my inverter has some sort of function to log this data, the fridge is the only thing that really runs during the day and is only 300w. I will need to install a wattmeter and see what it's using over 24 hours.
I dont occupy the place much during the week, so power demands are low, we only run lights which are all LED, a TV and the gas califont.
I was hoping to be able to run a washing machine, dishwasher and use a toaster and kettle if possible instead of gas. I don't run these on a daily basis.
 
How many panels are actually connected to your charge controller and in what format (series/parallel)?

From your image you're only getting around 300W!

You really, really need to get your pack fully charged, from mains or genset if necessary, lead-acid cells of any flavour don't like being partially charged. Fill 'em up!
 
How many panels are actually connected to your charge controller and in what format (series/parallel)?

From your image you're only getting around 300W!

You really, really need to get your pack fully charged, from mains or genset if necessary, lead-acid cells of any flavour don't like being partially charged. Fill 'em up!
OK, that's not much!
I need to really get up at first light and see what this bank is getting once charging commences.
The panels are 2S2P and 50V each and 420W giving 1600W and 100V
My batteries are also 2S2P configured for 24V.
My question is if these batteries are nearing full charge if it's only taking 300W of power?
 
The screen shot indicates the battery is almost charged. If you could determine the actual current into the battery is would be useful.
The 9 amps may indicate battery Input and inverter use. Even 9 amps Into the battery is 2% tail current.

As I stated earlier if the 540 Ah battery current falls below 1%C, 5 amps at 29 volts, then it's near enough charged.

Don't get confused by the fact that near full charge the battery will only accept a low charge current, this is normal for lead acid. This is nothing to do with the controller or solar array, its down to lead acid charging.

Mike
 
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The screen shot indicates the battery is almost charged. If you could determine the actual current into the battery is would be useful.
The 9 amps may indicate battery Input and inverter use. Even 9 amps Into the battery is 2% tail current.

As I stated earlier if the battery current falls below 1%C, 5 amps at 29 volts the its near enough charged.

Don't get confused by the fact that near full charge the battery will only accept a low charge current, this is normal for lead acid. This is nothing to do with the controller or solar array, its down to lead acid charging.

Mike
I tend to think this is the case too.
The inverter may have been on, but I wasn't checking, the only thing that would be taking any power would be if the fridge motor was running.
I will see if I can find a clamp meter and check the current. I know it was reading lower the other day, but was closer to float level around 28V I think.
Do these charge controllers have a built in current transformer to measure current tbatbit displays? If so, I would assume it should be fairly accurate?
 
I'm not a lead-acid man, we went directly to LiFePO4 but the volt drop does seem significant on load.

What size wires do you have controller to batteries, between batteries, and batteries to inverter?

Any fuses / breakers / isolators etc.??
 
From your very first post I noticed your usage of high draw appliances is pretty substantial especially with such a small battery bank. Your dishwasher should be set to "Air Dry" if it already isn't. Making heat from batteries is a huge draw and when your dishwasher goes into dry cycle it turns on that big element in the bottom of the tub, pulling a lot of current.

You're really asking a lot from your 4 batteries. Next time around you really should double the size of your bank and add those old panels into your array.
 
The way I always treated my lead acid batteries was to look at their voltage under a very light load or no load at all ... When I would run my microwave for a little bit they would drop down to like 11 volts sometimes.. but this was simply an under load voltage... They would go into the mid-12s or higher once the load was removed.. that's not only healthy but completely normal with that chemistry
 
I'm not a lead-acid man, we went directly to LiFePO4 but the volt drop does seem significant on load.

What size wires do you have controller to batteries, between batteries, and batteries to inverter?

Any fuses / breakers / isolators etc.??
8mm cable to the batteries from the controller I think. I know it was rated for more than enough current when I checked.
I think its a 60A breaker between the panels and controller, not sure on exact size of cables to inverter but its pretty heavy, at least 12mm diameter with chunky terminals.
Only fuse is the one built into the inverter.
 
From your very first post I noticed your usage of high draw appliances is pretty substantial especially with such a small battery bank. Your dishwasher should be set to "Air Dry" if it already isn't. Making heat from batteries is a huge draw and when your dishwasher goes into dry cycle it turns on that big element in the bottom of the tub, pulling a lot of current.

You're really asking a lot from your 4 batteries. Next time around you really should double the size of your bank and add those old panels into your array.
I figured it was probably asking a bit much but also figured that I would typically run the dishwasher during the day when there is sun, I would have needed double the panels if I doubled the battery capacity and this is really just a temporary measure until I get round to upgrading to something better in say 5 years. We just needed things to work and use the toaster without needing the genset to use it.
It did cut out during the drying phase iirc. I didn't think its element would stay on as long as it did.
I will be adding the extra panels, but not sure if I should go epever or not with those. I will need 2 more smaller controllers, would be good if I can link them all up together.
If I had this set up as a 48V bank, I don't think I would have had the same issue with it cutting off so fast, as the batteries would deliver the same power with half the current.
 
The way I always treated my lead acid batteries was to look at their voltage under a very light load or no load at all ... When I would run my microwave for a little bit they would drop down to like 11 volts sometimes.. but this was simply an under load voltage... They would go into the mid-12s or higher once the load was removed.. that's not only healthy but completely normal with that chemistry
Well that's pretty much what I observed myself too. I think my batteries were just getting down at the end of the day and couldn't cope with the current.
 
Do these charge controllers have a built in current transformer to measure current tbatbit displays? If so, I would assume it should be fairly accurate?
The charge controller is measuring current supplied to your system, reasonably accurate. If your inverter is connected along with other circuits, then they will be taking current. You need to disconnect everything from the battery except the solar controller, or use a clamp meter on the battery feed cable.
The current will always be low into the battery on float charge.

I don't think you have a serious issue, although as in most applications more solar and more battery

Charging does not seem too bad, a longer absorption time, boost duration, would help.
The volt drop on heavy load is expected and normal for lead acid.

Note as the discharge current increases the effective battery capacity decreases, (Peukert's Law). At low temperatures the effective capacity is also reduced.
battery capacity.jpg

AGM battery for dally cycled applications is not the best solution for solar systems due to the limited solar hours.
If its a standby system with infrequent discharges then not too bad as the lost charge can be recovered over a few days.

However, you have what you have, its usable, but don't expect a long service life from your battery back.
Having some sort of battery monitor will help battery management, but must be a type that allows for charge efficiency and Peukert's constant.

Mike
 
I figured it was probably asking a bit much but also figured that I would typically run the dishwasher during the day when there is sun, I would have needed double the panels if I doubled the battery capacity and this is really just a temporary measure until I get round to upgrading to something better in say 5 years. We just needed things to work and use the toaster without needing the genset to use it.
It did cut out during the drying phase iirc. I didn't think its element would stay on as long as it did.
I will be adding the extra panels, but not sure if I should go epever or not with those. I will need 2 more smaller controllers, would be good if I can link them all up together.
If I had this set up as a 48V bank, I don't think I would have had the same issue with it cutting off so fast, as the batteries would deliver the same power with half the current.
This might help ease your mind about overpanneling your controller.
If you were to wire your bank at 48 volts it will cut the current loads in half but you are still using the same amount of power, just at higher voltage. Still think you are over burdening your batteries with the size of your daily loads. Even one more pair of AGM's would help.


EPever over panel chart.jpg
 
That's interesting considering my charger does not even display it as a setting anywhere. It must be just a preset profile from factory or something? ?
 
The charge controller is measuring current supplied to your system, reasonably accurate. If your inverter is connected along with other circuits, then they will be taking current. You need to disconnect everything from the battery except the solar controller, or use a clamp meter on the battery feed cable.
The current will always be low into the battery on float charge.

I don't think you have a serious issue, although as in most applications more solar and more battery

Charging does not seem too bad, a longer absorption time, boost duration, would help.
The volt drop on heavy load is expected and normal for lead acid.

Note as the discharge current increases the effective battery capacity decreases, (Peukert's Law). At low temperatures the effective capacity is also reduced.
battery capacity.jpg

AGM battery for dally cycled applications is not the best solution for solar systems due to the limited solar hours.
If its a standby system with infrequent discharges then not too bad as the lost charge can be recovered over a few days.

However, you have what you have, its usable, but don't expect a long service life from your battery back.
Having some sort of battery monitor will help battery management, but must be a type that allows for charge efficiency and Peukert's constant.

Mike
Thanks, ive increased the boost to its max which is 180mins anyway.
I dont have a huge demand for energy use at the moment, but I will be monitoring power usage to see what its using. From what I can tell, it appears to be charging OK.

This might help ease your mind about overpanneling your controller.
If you were to wire your bank at 48 volts it will cut the current loads in half but you are still using the same amount of power, just at higher voltage. Still think you are over burdening your batteries with the size of your daily loads. Even one more pair of AGM's would help.


EPever over panel chart.jpg
Ive got a tracer 6420AN, looking at its specs, I think I may already have more panel capacity than it can handle, seems its only capable of 1500W @24V and i have 1600W of panels on hand here connected to it. I was sure it was able to handle more than this at the time I ordered it, but im actually shy of 100W it seems.

I cant wire my bank as 48V or else I would have done so, I would need to find a 48V inverter othersiwse.
How many more panels ideally would I need if I was to add a couple more batteries? I was put off this idea because I was told that its not ideal to have more than 2 strings in parallel, (im assuming this is due to balancing issues)
 
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