Inverter and Battery Charging Question

Lucas61

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Jun 13, 2014
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This guy explains it well.

A BMS will make sure it does not drop below 50% or whatever your manufacturer recommends. It will also monitor the temperature of the cells to make sure it does not overheat or overcharge.
First YT video. This guy states the paradox: You don't want to discharge a battery too much but the whole point of the battery, to use it, is to discharge it. He says that a discharge should not be below 50%. I will check my manual and see if there is a way to program it to shudown at 50%. Also, he talks about overcharging. I'm charging from 120 V AC. I have no idea if this is appropriate. He mentioned 20% -- maybe I can set the charging rate. It's possible that I messed up, this being my first time using an inverter/battery. It's possible I did not program it properly to preserve the battery. I'll find out when I ook at my manual. I'm still not getting an answer to the question: Why can I not re-charge the battery just like a car battery? It's the same technology.
 

reilleyp

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Dec 12, 2006
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First YT video. This guy states the paradox: You don't want to discharge a battery too much but the whole point of the battery, to use it, is to discharge it. He says that a discharge should not be below 50%. I will check my manual and see if there is a way to program it to shudown at 50%. Also, he talks about overcharging. I'm charging from 120 V AC. I have no idea if this is appropriate. He mentioned 20% -- maybe I can set the charging rate. It's possible that I messed up, this being my first time using an inverter/battery. It's possible I did not program it properly to preserve the battery. I'll find out when I ook at my manual. I'm still not getting an answer to the question: Why can I not re-charge the battery just like a car battery? It's the same technology.
When you start your car every day it takes a little bit of the energy from the battery but it does not discharge it down to 0%. While you are driving the alternator recharges your battery. I am sure your car has electronics to regulate how quickly it charges the battery and stops charging when it is fully charged similar to your battery management system with your inverter. Otherwise your car battery would explode by the time you drive from New York to California.
When your alternator fails in your car you do not notice immediately. Sometimes you can continue to drive but eventually your lights will dim and drain your battery down to zero. Often times when your alternator dies and you abuse the battery you will also need a new battery. To finally answer your question if you had a bad alternator in your car every day and you drew your car battery down to 0% every day then it would not last five years. The battery will probably only last a few months.
 

Cdn_Gringo

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Apr 29, 2014
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Why cannot I re-charge my battery just as you would a insufficiently charged car battery? But if I can do that, how do I do that?

The takeaway here is that even if your inverter is recharging and maintaining your battery(s) charge state as efficiently as possible, all batteries weaken and hold less of a charge over time. The more times the battery is used and then recharged, the faster it reaches it's end of life. All batteries, be they in cellphones, cars, inverter systems or elsewhere can only be recharged so many times before they begin to weaken. Eventually you will notice a big drop in the number of hours your battery can provide power to your house when the street power is off.

At this point, when the useful time frame has become so short as to be considered insufficient, the only remedy is a new battery. In your case with such frequent outages, if you can swing it you should consider replacing your single battery with a bank of four new ones. This will help spread the power drain across all four so unlike your a single battery that gets thrashed severely by your frequent power outages the bank of batteries share the load and each takes a lessor hit. But a recharge cycle is a recharge cycle and each cycle brings you one cycle closer to the end of the of useful life of each battery.
 

johne

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I can relate to the car battery charging and recharging. Every 4 weeks I return to the states and spend about 12 days in the states and return to the DR. Up until about a year ago most times, especially in the winter months, my car/truck is in the south, my battery was dead. I'd get a jump, loose a couple of hours of valuble time and be on my way. BUT my new battery lasted a very short period of time. I bought a new battery and someone said well, why don't you just disconnect one cable to the battery. Takes about 2 minutes counting finding the latch to open the hood. Never had a battery failure since then.
 
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chico bill

Dogs Better than People
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Four when I replace? Not happening. That would cost $2,400.00. It is sealed lead acid. You don't have to top off because it's sealed, in fact, you can't. What I'm still not understanding are: a. Why can I not re-charge my inverter's battery just like you would an undercharged car battery?, b. It seems like my inverter/battery has been doing exactly what such a system does when the power goes off. What did I do wrong or is this normal functioning?
I just bought 4 NAPA 6 volts for $9500 pesos each
 
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Seamonkey

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Maybe as a member here suggested here, I need to check my manual, since my inverter is programmable, and see if I can implement a discharge cutooff. Meanwhile, I don't think anyone has suggested a solution. Why cannot I re-charge my battery just as you would a insufficiently charged car battery? But if I can do that, how do I do that?

Further, if charging > 50% is verboten, then, really, what's the point in even bothering with an inverter?? The use of 50% of one battery is almost useless. And that setup costs $1,000.
You need a bigger battery bank. More amp hours will give you longer time before you reach 50%.
 

cavok

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"Just a small" will set you back about $1,000 USD -- $600.00 for a sealed battery and $400.00 for the inverter. Yes, the battery costs more than the inverter.
I think you're talking about a high-tech inverter at that price and I'm pretty sure you can get a Trojan T-105 deep cycle battery for around $200 to $225 USD(?).
 

cavok

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Maybe as a member here suggested here, I need to check my manual, since my inverter is programmable, and see if I can implement a discharge cutooff. Meanwhile, I don't think anyone has suggested a solution. Why cannot I re-charge my battery just as you would a insufficiently charged car battery? But if I can do that, how do I do that?

Further, if charging > 50% is verboten, then, really, what's the point in even bothering with an inverter?? The use of 50% of one battery is almost useless. And that setup costs $1,000.
When the power comes back on, your inverter charges the battery. You can charge a battery at any discharge level. Slow charge rates are better for the battery. Very high charge rates can cause the acid to boil.
 

Tradewinds

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Oct 7, 2017
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I can see Lucas' point, we live on a boat on Vancouver Island strictly on batteries at anchor. I just bought 6 x 6volt at 250 amp/hrs ea = total of 12 volts 750 amp/hrs.
We bought AGM lead acid sealed batteries ($300 CAD ea) and were kinda choked to learn about the 50% safe drawdown recommendation. That gives me a useful 375 amp/hrs. Ouch!
The same 6 lithium batteries can be drawn down to 20% meaning I could have used only 4 lithium batteries, helping with the cost. They can also be charged at a much higher rate and they weigh a lot less too.
These 6 batteries can't power much. We have a 5 amp frig, led lighting, inverter, and a 6 amp heater in winter. Our 600 w of solar is great all summer but come September we need to run the Honda genset for an hour a day, going into 2 hours in October, going into you know the rest.

Wrapping up, ya always need more batteries than ya think, esp with all the little charging devices adding up.
 

reilleyp

Well-known member
Dec 12, 2006
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I can see Lucas' point, we live on a boat on Vancouver Island strictly on batteries at anchor. I just bought 6 x 6volt at 250 amp/hrs ea = total of 12 volts 750 amp/hrs.
We bought AGM lead acid sealed batteries ($300 CAD ea) and were kinda choked to learn about the 50% safe drawdown recommendation. That gives me a useful 375 amp/hrs. Ouch!
The same 6 lithium batteries can be drawn down to 20% meaning I could have used only 4 lithium batteries, helping with the cost. They can also be charged at a much higher rate and they weigh a lot less too.
These 6 batteries can't power much. We have a 5 amp frig, led lighting, inverter, and a 6 amp heater in winter. Our 600 w of solar is great all summer but come September we need to run the Honda genset for an hour a day, going into 2 hours in October, going into you know the rest.

Wrapping up, ya always need more batteries than ya think, esp with all the little charging devices adding up.
Be careful buying the cheapest LiFePo4 batteries available. They are a scam from China. I bought some and the cost to ship them back is super expensive. Spend a little more for a seller in your country, buy one or two, test them and if they are legit, buy the rest.
 

chico bill

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May 6, 2016
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I think you're talking about a high-tech inverter at that price and I'm pretty sure you can get a Trojan T-105 deep cycle battery for around $200 to $225 USD(?).
10,000 pesos for each Trojan 105 Red
 
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JD Jones

Moderator - Covid 19 in DR & North Coast
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10,000 pesos for each Trojan 105 Red
They seem to be dropping a little here on the South Coast. I'm seeing quite a few in the mid 9K range.

I will probably go with the Red's once I have to replace mine.
 

chico bill

Dogs Better than People
May 6, 2016
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They seem to be dropping a little here on the South Coast. I'm seeing quite a few in the mid 9K range.

I will probably go with the Red's once I have to replace mine.
I like my NAPA brand. Less rated AMP hours than the Trojan (but cheaper) but they don't seem to need water top offs and I like being able to open 3 cells on the battery at once instead of having to unscrew and screw back 12 individual caps on my 4 batteries
 

Lucas61

Well-known member
Jun 13, 2014
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retired English teacher (30 years)
The takeaway here is that even if your inverter is recharging and maintaining your battery(s) charge state as efficiently as possible, all batteries weaken and hold less of a charge over time. The more times the battery is used and then recharged, the faster it reaches it's end of life. All batteries, be they in cellphones, cars, inverter systems or elsewhere can only be recharged so many times before they begin to weaken. Eventually you will notice a big drop in the number of hours your battery can provide power to your house when the street power is off.

At this point, when the useful time frame has become so short as to be considered insufficient, the only remedy is a new battery. In your case with such frequent outages, if you can swing it you should consider replacing your single battery with a bank of four new ones. This will help spread the power drain across all four so unlike your a single battery that gets thrashed severely by your frequent power outages the bank of batteries share the load and each takes a lessor hit. But a recharge cycle is a recharge cycle and each cycle brings you one cycle closer to the end of the of useful life of each battery.
In your scenario, all batteries reach EOL. True, but in the meanwhile, those same batteries can be re-charged, and remain effective, a limited number of times. So, if I have not recharged my inverter's battery one time, why can't I do that?
 

Lucas61

Well-known member
Jun 13, 2014
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retired English teacher (30 years)
I think you're talking about a high-tech inverter at that price and I'm pretty sure you can get a Trojan T-105 deep cycle battery for around $200 to $225 USD(?).
My high-tech PowerTek inverter (digital) costs only about $100.00 more than the low-tech one (analog). The cost is in the battery. So much so, that for me, I cannot afford more than one. Before I ran into my problem we were going about 18 hours before shutdown, which was not great but O.K. And that was with fridge and computers off, just a few lights and fans.
 

Cdn_Gringo

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Apr 29, 2014
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So, if I have not recharged my inverter's battery one time, why can't I do that?

I do not really understand your question so I reread your OP. Having stated that you suffer through a lot of power outages, it follows that your inverter attempts to recharge the single battery after every outage. I don't see where "if I have not recharged my inverter's battery one time, why can't I do that?" comes into play. If you are only getting 1 hour of backup power from that battery, it is clearly toast and needs to be replaced. I don't know how your inverter knows to stop charging and report the batteries at 100% so I won't guess. Regardless your battery is charging to no where near 100%. All of the advice given pertains to getting the longest useful life out of your system but once the battery stops working well, there is nothing you can do to "rejuvenate" it. Not what you want to hear but I see a shopping trip in your future. Want your inverter to be able to supply power during an outage for longer that it does now get a new battery. Want to prolong the useful life of your heavily worked battery and enjoy an even longer period of backup power, buy and connect more than one new battery.
 

johne

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HavinAll of the advice given pertains to getting the longest useful life out of your system but once the battery stops working well, there is nothing you can do to "rejuvenate" it. Not what you want to hear but
It's just not like a "Lazurus" event to put it another way.
 

cavok

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Spending $600 for an AGM battery vs $200 for a standard lead/acid battery doesn't seem very cost effective to me, especially when the AGM batteries are only recommended to be discharged 50% vs 80% for a standard lead/acid and only last one year vs several years. That's a lot of money just to save yourself the "hassle" of adding some water to your battery every once in a while. Just what are you getting for all that extra money?