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Old 05-26-2012, 12:35 PM   #1
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battery calculations?

I am trying to use my inverter continuously so that my TV antenna doesn't shut down and require rebooting...and our small load stuff will stay up. Then run the generator 4-5 hours a day to recharge.

I am not sure if I have a battery problem or just don't know how to recognize normal operation. I have 4 6volt batteties

When the generator gets to float level and I shut it off. The inverter screen says my batteries are at about 12.7 volts. With a load of around 25 amps..per the inverter screen...the battery voltage drops pretty quickly....down into the mid 11's within a few hours or so.

The 25 amp load is produced by a tv, a direct tv receiver, a few cell phone chargers, a play station, a computer charger...nothing much more than that.

Does all of the above seem within normal parameters or are my batteries discharging faster than normal?
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Old 05-26-2012, 12:56 PM   #2
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Quote:
Originally Posted by litespeed View Post
I am trying to use my inverter continuously so that my TV antenna doesn't shut down and require rebooting...and our small load stuff will stay up. Then run the generator 4-5 hours a day to recharge.

I am not sure if I have a battery problem or just don't know how to recognize normal operation. I have 4 6volt batteties

When the generator gets to float level and I shut it off. The inverter screen says my batteries are at about 12.7 volts. With a load of around 25 amps..per the inverter screen...the battery voltage drops pretty quickly....down into the mid 11's within a few hours or so.

The 25 amp load is produced by a tv, a direct tv receiver, a few cell phone chargers, a play station, a computer charger...nothing much more than that.

Does all of the above seem within normal parameters or are my batteries discharging faster than normal?
What is the amp hour rating of the 6 volt batteries?
How old are they and have you load tested them to see what shape they
are in?
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Old 05-26-2012, 01:59 PM   #3
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Quote:
Originally Posted by litespeed View Post
I am trying to use my inverter continuously so that my TV antenna doesn't shut down and require rebooting...and our small load stuff will stay up. Then run the generator 4-5 hours a day to recharge.

I am not sure if I have a battery problem or just don't know how to recognize normal operation. I have 4 6volt batteties

When the generator gets to float level and I shut it off. The inverter screen says my batteries are at about 12.7 volts. With a load of around 25 amps..per the inverter screen...the battery voltage drops pretty quickly....down into the mid 11's within a few hours or so.

The 25 amp load is produced by a tv, a direct tv receiver, a few cell phone chargers, a play station, a computer charger...nothing much more than that.

Does all of the above seem within normal parameters or are my batteries discharging faster than normal?
That sounds like it's about the way mine work, I use a Cpap and I turn the inverter on at night, even with a full charge on the batteries the batteries won't run the inverter/cpap all night. I think my batteries should last all night but I'm not smart enough to figure it out. If I leave the inverter off the batteries are fine the next morning and will run the overhead fans all night and day. Since I'm not smart enough to figure it out (basically I'm just too lazy to fool with it) I use a Honda 2000 generator to supplement my batteries. I can fill the generator with one gallon of gas at night, crank it up and it'll run all night long charging my batteries and running my cpap. When I wake up the next morning I turn the generator off.

PS. It only take a couple of minute for my directtv receiver to update after I remove the power from it and put power back to it.
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Old 05-26-2012, 02:27 PM   #4
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We have four Interstate U-2200's, they run the TV's, the furnace, the satellite box, the controls for the refer (refer on gas), the U-Line ice maker, the storage bay freezerm my CPAP and everything else we might turn on except the Advantium microwave/convection oven. Sometimes we are down to 11.9 volts in the morning though.
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Old 05-28-2012, 07:42 AM   #5
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Well, you say you are down to 11.9 by the morning, but that it not really the true reading of the batteries. This is due to the current load on the batteries. The true state of the batteries can only be read with all loads off and a standing reading taken. These batteries would probably read 12.3 if all loads were removed and let stand for a short period.

This is applied to all auto generator starting systems. For example if you set an auto start at 12.3 vdc, the generator would be starting every time you applied any reasonable load. 12.3, by the way is 50% charge, a state that you do not want to go below. So, all auto generator starting systems are usually set to start at 11.7 to 11.9. The former being more used.

Additionally it would be good to read your battery state at the batteries with a multi-meter. This would be far more accurate as there is no wiring voltage loss.

I guess what I'm saying, is your batteries may be working correctly. If you have an issue, there is a chance your charging system may not be fully charging your batteries. This is quite common.

I had an '02 DSDP and experienced similar issues. I replaced the charger/converter with a better unit. It was like night and day. The batteries charged fully. It was like I installed twice the size battery bank.

Anyway, hope this helps.

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Old 05-28-2012, 09:21 AM   #6
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You should only use about 50% of the battery capacity. Two 6v batteries have about 220 amps capacity, four have about 440 capacity. Using half of that gives you 220 amps available.

Knowing your available available amps the length between charges is dependent on the amps being used. 220 amps with a load of 25 amps should give you about 8.8 hours of use before recharging.

Reducing the load or adding more batteries will give you a longer run time.

You could reduce the generator run time by just charging to about 80%. This should only take about an hour. A run in the morning and a run in the evening. About once a week charge up to the float stage like you do now.
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