Battery question

[paphil]

We recently installed 4 6 volt batteries with 2000 watt converter/charger. We are on our first dry camping extended stay and I think we have a problem. According to this:

Four T-105, 6V Batteries rated at 225AH Connected in Series/Parallel

System Voltage: 6V + 6V = 12V
System Capacity = 225AH + 225AH = 450AH

we should be able to run a freezer which is rated at DC 4.5A, my husbands c-pap with humidifier at about 5 amps, and a vernado fan on low for 10 hours without running our batteries below 40 percent each night. Are my numbers wrong or do we have a problem with the batteries?

thanks,
Pam

[Cate&Rob]

Pam,

How are you recharging the batteries? It takes a long time to regain the top 20% of charge and discharging below 50% (even for deep-cycle batteries) is not ideal. If you are using an inverter to power the CPAP, many of these will shut off when they sense that the battery bank is at 50%. There are also other draws on your batteries such as the control circuits for the fridge and water heater, even if these are operating on propane.

Stil . . . your numbers should work. It is a good idea to size your system to operate within 30% of the nominal Ah capacity, cycling between 80% charge and 50% charge. 30% of 450 is 135 Ah. The freezer at 50% duty cycle is 54 Ah per day. The CPAP for 8 hrs is 40 Ah and the fan at maybe 2 amps is 20 Ah. That's 114 of the 135 target.

If you can charge to higher than 80% (solar maybe) that would be a good thing.

Rob

[carnolddsm]

How are you determining charge? Voltage or a meter measuring amps used?

If you are using an amps used meter, generally the meters have to be programmed with the battery capacity. Would suggest checking the settings.

And Rob is correct, it takes a long time to charge lead acid batteries past 80%.

[paphil]

We are charging with generator. It takes about 3.5 hours with the honda 3000 with eco off. I'm using the inside panel/remote that came with the inverter to monitor the batteries. By the time we turn off the generator, the batteries have gone into float charge so I'm assuming they are 100 percent charged. My husband is going into town today to buy a hydrometer to make sure the batteries don't have a bad cell. BUT, it just seems to me that with the four of them, we should not be drawing down to around 40 percent overnight. If this is the case, and there is nothing wrong with the battieries, we are going to have to add another two 6 volt batteries.

[Cate&Rob]

Three hours does not sound like enough time to reach float stage from discharged (40%).
As Colan suggests, an Ah meter set to the parameters of your bank would help you to really understand how much is being used and how much is being replaced. Something like the Victron BMV700 https://www.amazon.com/Victron-BMV-7.../dp/B00MJ85E2U

From http://batteryuniversity.com/learn/a...d_acid_battery
"the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours"

Rob

[paphil]

Strangely enough I have that monitor installed also. It has different readings that the monitor from the inverter. It shows the battery dropping to 70 percent overnight. Should I assume that it is more accurate than this one: http://gpelectric.com/products/inverter-charger-remote

[TucsonJim]

Pam,

How are you connected to the inverter? If you are running power to the whole coach, you need to make sure your converter is not powered up while the inverter is on. It will cause your batteries to quickly deplete. On my set up, I have to turn off the converter at the breaker panel when I'm running on inverter power.

[Cate&Rob]

Strangely enough I have that monitor installed also. It has different readings that the monitor from the inverter. It shows the battery dropping to 70 percent overnight. Should I assume that it is more accurate than this one: http://gpelectric.com/products/inverter-charger-remote

You battery bank dropping to 70% overnight fits a lot better with your other numbers . I have had the Victron monitor on my boat for many years and trust that it is giving me good information. It is important that you set it up with the correct specs for your battery bank and index it to 100% after the batteries have been on charge for at least 24 hrs. It would be good to try and figure out why the two monitors are giving such dramatically different readings.

Rob

[paphil]

We removed the converter since this inverter has a charger. Here is a picture of both monitors:

[N6ZCM1]

Hello Pam...

Trying to understand your power usage... I would take it then you have an Inverter to provide 120 volts to the trailer.
Define this Freezer Model number? you say DC 4.5 amps... Your Cpap device... is this plugged into 120v? Vernado fan which model is this?
Is your fridge on LP only, on Auto it would select 120 volt since the inverter is on.

Dale