306w load, 2 x 100ah batteries, only lasting 1 hour

SianD said:
Hi everyone. I'm having a problem with my mecer 2.4kva trolley inverter. I have 2 x 100ah deep cycle batteries and I'm running a load of 306w. After 1 hour the battery indicator on the inverter display drops to 50%. Someone tested the batteries fir me today with a multimeter and they both gave a reading of 14v. Don't understand why they are dropping to 50% after 1 hour. They used to last over 4 hours before dropping to 50%. What could the problem be as from testing the batteries today it would seem they are still fine. Thanks
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They gave a reading of 14v because they were still on charge. Voltage output (not the charger voltage, the battery voltage) is only half the equation when it comes to battery health.
 
SianD said:
Hi everyone. I'm having a problem with my mecer 2.4kva trolley inverter. I have 2 x 100ah deep cycle batteries and I'm running a load of 306w. After 1 hour the battery indicator on the inverter display drops to 50%. Someone tested the batteries fir me today with a multimeter and they both gave a reading of 14v. Don't understand why they are dropping to 50% after 1 hour. They used to last over 4 hours before dropping to 50%. What could the problem be as from testing the batteries today it would seem they are still fine. Thanks
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How old are the batteries ?
 
Christopher is 100% correct...

Let's start with your battery bank,

12v 100ah battery must not be discharged deeper than 50%, if your system is a 12v system and you have two batteries then you actually only have 100ah available so without losses you have a maximum of 12v x 100ah = 1200va or 1.2 kva... If your system is 24v then you have the same kva but higher voltage.

Now your load: 306w x 4 hours equals 1224w or 1.224kw not considering losses (usually the mecer systems are not very effective in changing dc power to ac power so we devide your load by 0.9 to give a reflection of 90% efficacy = 1.224kw / 0.9 = 1.36kw...

Your battery bank has less kw available than you are drawing with your inverter, this causes lead acid and/or gel batteries to degrade to the point where they are unable to hold the same charge...

You will need to replace your batteries, the only way that you would be able to run your system for the 4 hour loadshedding without damaging batteries again and not needing to replace them again would be to lessen your load or change your battery to a lithium...

Sorry for the bad news...
 
Alpha Omega Solar said:
Christopher is 100% correct...

Let's start with your battery bank,

12v 100ah battery must not be discharged deeper than 50%, if your system is a 12v system and you have two batteries then you actually only have 100ah available so without losses you have a maximum of 12v x 100ah = 1200va or 1.2 kva... If your system is 24v then you have the same kva but higher voltage.

Now your load: 306w x 4 hours equals 1224w or 1.224kw not considering losses (usually the mecer systems are not very effective in changing dc power to ac power so we devide your load by 0.9 to give a reflection of 90% efficacy = 1.224kw / 0.9 = 1.36kw...

Your battery bank has less kw available than you are drawing with your inverter, this causes lead acid and/or gel batteries to degrade to the point where they are unable to hold the same charge...

You will need to replace your batteries, the only way that you would be able to run your system for the 4 hour loadshedding without damaging batteries again and not needing to replace them again would be to lessen your load or change your battery to a lithium...

Sorry for the bad news...
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While your post on the whole is accurate, your inability to differentiate between kW and kWh creates unnecessary confusion. For someone marketing themselves as a solar guy, I'd expect better.
 
Speedster said:
While your post on the whole is accurate, your inability to differentiate between kW and kWh creates unnecessary confusion. For someone marketing themselves as a solar guy, I'd expect better.
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Oh I am so sorry...

Let me correct myself,

12v 100ah battery must not be discharged deeper than 50%, if your system is a 12v system and you have two batteries then you actually only have 100ah available so without losses you have a maximum of 12v x 100ah = 1200va or 1.2 kva... If your system is 24v then you have the same kva but higher voltage.

Now your load: 306w/h x 4 hours equals 1224w or 1.224kw not considering losses (usually the mecer systems are not very effective in changing dc power to ac power so we devide your load by 0.9 to give a reflection of 90% efficacy = 1.224kw / 0.9 = 1.36kw...

Your battery bank has less kw available than you are drawing with your inverter, this causes lead acid and/or gel batteries to degrade to the point where they are unable to hold the same charge...

You will need to replace your batteries, the only way that you would be able to run your system for the 4 hour loadshedding without damaging batteries again and not needing to replace them again would be to lessen your load or change your battery to a lithium...

Sorry for the bad news...
 
And then comes the peukert losses to get 100% of the capacity you need to draw less tha c/20

Edit :Tldr you need one 100ah battery for every 64w you pull, ie 640w you need 10 x 100ah batteries to be able to not have peukert losses not a big deal if you have losses, but your calc of 50% capacity is off if you do have losses , ie most people are damaging their batteries following the rule of thumb calculations (now naturally this uses another rule of thumb ie c/20 not all batteries are equal some less prone than others)

So on a100ah battery that is 64w from a single 100ah battery

So to not discharge under 50% and pull through 4 hrs you need a bank bigger than 235ah on 24v

Scaled down if only tv you need about 100-150ah in lead acid (tv dependant do set down the brightness to help)

Or you are damaging the battery

Hence why Just buy lithium
Lithium isn't victim to this it doesn't mind pulling high c

Naturally this does not include degradation ie the moment the battery has degraded enough for your load to pull it under 50% the race to the bottom of failed batteries speed up

Edited had a blonde moment
 
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If calculating capacity you actually need to use a calculator that compensates for peukert

Some require more fields than others and specs we might not have access to hence the rule of thumb of pulling less than c/20 (salt naturally kinda new to peukert) for no losses

Or just have a volt readout on your battery and do the shutdown at the correct voltage

Peukert Number Battery Life Calculator

www.csgnetwork.com
 
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howardb said:
What age are the batteries? Our similar setup with that trolly inverter years ago also originally lasted over 4 hrs, but after about 2 years of various loadshedding cycles, the batteries would not hold full charge for long, even though they tested with good voltage - I had to replace them.
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Thanks Howard. We've been using it for 20 months so they are coming up to 2 years old. Was just so confusing when the guy came to test the batteries and said they were absolutely fine, but I've had some good replies to my question so it's making abit more sense now. Reassuring to hear you ended up in the same position with yours. Thanks for your comment.
 
ld13 said:
24v? So 24x100ah=2400wh capacity on those batteries, when they were brand new.
You were able to run a 306W load for 4 hours back then = 1224wh draw over 4 hours. Not exactly optimal, as you have to work in some inefficency losses, so ~85%? becomes 1440wh or up to 60% DOD (depth of discharge) on the battery side. Did you let the batteries charge up to 100% full after each 4 hour run? No? So you might've hit more than 60% DOD right there.

Even ignoring the efficiencies, you were already running the batteries down more than 50% of their capacity with each 4 hour stint. Lead acids hate that. They start degrading immediately. So with each subsequent run you hit them even harder, every time over 50%.

I have seen multiple battery banks die within a year due to exactly this: The peeps calculate their usage. Even working in the inefficiencies of the inverter. They calculate the batteries they need at 50% DOD, and then forget to work in any headroom for additional usage etc.
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Thanks Id13. For us poor souls who are not clued up on any of this, all I could do was trust the battery indicator on the led panel on the inverter, and I made sure that never weren't lower that 50%. If I understand correctly now, those displays are not accurate?
 
SianD said:
Thanks Howard. We've been using it for 20 months so they are coming up to 2 years old. Was just so confusing when the guy came to test the batteries and said they were absolutely fine, but I've had some good replies to my question so it's making abit more sense now. Reassuring to hear you ended up in the same position with yours. Thanks for your comment.
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The fact that he measured 14v says nothing about the batteries state. That's not how you determine if the batteries are fine.
 
Alpha Omega Solar said:
Oh I am so sorry...

Let me correct myself,

12v 100ah battery must not be discharged deeper than 50%, if your system is a 12v system and you have two batteries then you actually only have 100ah available so without losses you have a maximum of 12v x 100ah = 1200va or 1.2 kva... If your system is 24v then you have the same kva but higher voltage.

Now your load: 306w/h x 4 hours equals 1224w or 1.224kw not considering losses (usually the mecer systems are not very effective in changing dc power to ac power so we devide your load by 0.9 to give a reflection of 90% efficacy = 1.224kw / 0.9 = 1.36kw...

Your battery bank has less kw available than you are drawing with your inverter, this causes lead acid and/or gel batteries to degrade to the point where they are unable to hold the same charge...

You will need to replace your batteries, the only way that you would be able to run your system for the 4 hour loadshedding without damaging batteries again and not needing to replace them again would be to lessen your load or change your battery to a lithium...

Sorry for the bad news...
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You're actually going backwards which is even more concerning as it shows your previous post wasn't just a bit careless, you actually don't understand the concepts.
 
Not_original said:
They gave a reading of 14v because they were still on charge. Voltage output (not the charger voltage, the battery voltage) is only half the equation when it comes to battery health.
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So what other factors do I need to check other than voltage and how do I do that please?
 
Alpha Omega Solar said:
Let me correct myself,

12v 100ah battery must not be discharged deeper than 50%, if your system is a 12v system and you have two batteries then you actually only have 100ah available so without losses you have a maximum of 12v x 100ah = 1200va or 1.2 kva... [!!!] If your system is 24v then you have the same kva but higher voltage.

Now your load: 306w/h [WTF!!!] x 4 hours equals 1224w or 1.224kw not considering losses (usually the mecer systems are not very effective in changing dc power to ac power so we devide your load by 0.9 to give a reflection of 90% efficacy = 1.224kw / 0.9 = 1.36kw...

Your battery bank has less kw [aish!] available than you are drawing with your inverter, this causes lead acid and/or gel batteries to degrade to the point where they are unable to hold the same charge...
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Am I missing the joke or is this the just the state of play in solar and batteries today! Ex Blind sales-man leading the blind when it comes to kWh and kW!
 
Speedster said:
You're actually going backwards which is even more concerning as it shows your previous post wasn't just a bit careless, you actually don't understand the concepts.
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He understands the concepts
I had the same issue a while back ,ie blonde moment

The way i expressed my thoughts if reading the post you can see i get the concept
Just not using the terms as the Zeitgeist does

Essentially a grammer nazi situation
 
B-1 said:
The fact that he measured 14v says nothing about the batteries state. That's not how you determine if the batteries are fine.
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Yeh. Was going to say that.

A battery's voltage needs to be tested under load... Not open circuit like that. Which is exactly what you mecer is doing -- telling you the voltage has dropped to a 50% level when the load is on...

You may have hurt the batteries further than described above because they weren't fully charged before going back into another load shedding... In short you may have already used up all their cycles :(
 
StrontiumDog said:
@SianD how long have you had this setup? Mine were dying after 22 months due to constant stage 5-6 load shedding so I replaced them in month 23.

With my new batteries, in order to save them I plan on using the inverter mainly for my work setup, 2 monitors and a laptop. On the odd occasion I use it on my home/gaming PC I; won't be gaming on it because it's going to deplete the batteries too much.
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20 months. My confusion is the battery tester guy said the health of batteries is still very good so I'm trying to understand why it isn't working for longer than 1 hour anymore. I've had alot of replies now though saying the voltage is not the only thing that needs to be tested so just waiting for answers now on what else I should test. But at the end of the day I guess my batteries are just finished and it's time to div in to my life sayings again and buy something with lithium batteries.
 
B-1 said:
The fact that he measured 14v says nothing about the batteries state. That's not how you determine if the batteries are fine.
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So how do I actually determine if the batteries are fine please?
 
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