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Old 07-07-2019, 04:23 PM   #1
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How low a voltage is too low???

So my new Serenity 25rb doesn't seem to show the battery "%" just the voltage.

Since I didn't understand the phantom drains all over, the first time I went to pick it up after storing for a month, the batteries were dead, couldn't run the jack and the voltage read with my VOM was basically 0v (the phantom drains where still connected) .

The dealer said the batteries should recover and after hooking up my external solar they did but...

Yes they charge up. Yes the internal charger charges them. 12.6v after cutting off city power, but in the morning though, they are down to 11.9v without using lighting. The fridge is still working at 11.9v but I wonder how low is okay?

AND, what happened to the battery '%' metering my Bambi had?
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Old 07-07-2019, 05:36 PM   #2
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The dealer doesn't want to hassle with you about replacing the batteries. If my flooded lead-acid batteries read 0V with a multimeter across the battery terminals, I would write them off if I could afford to. Your 2019 trailer should probably have 2018 batteries which Interstate will probably replace under warranty if you haul the batteries to them.

Caveat: State of Charge estimation by voltage assumes a normal-ish temperature (say 70F) but you can make broad generalizations. And generally 11.9v is effectively discharged. There's a state-of-charge graphic chart and and a table of SoC by voltage on this handy page (bookmark it, it's useful.) The voltage meter in my Airstream reads nearly a full tenth lower than a multimeter on the battery terminals. I don't know if this is calibration, voltage drop to the point where the meter is attached, etc... I just correct for it in my head, since that reading is only good for guesstimation in the first place.

How long did you charge the batteries before running this test? If they ever did come back from 0V, it would probably take 2 days to fully charge them with the converter-charger in the Airstream.

On my 26U, after running my CPAP machine on the inverter for 7 hours or so, fridge running full time, lights, water pump, etc. but no fan use; starting out from a fairly full charge and no charging after about 6 PM, the voltage right when I shut off the inverter around 8 AM was 12.2 (50+ percent, remember mine reads low) and it read 12.4 about 20 minutes later when I was about to plug in the solar panels. If I were a gambling man, I'd bet that your batteries are done.
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Old 07-07-2019, 05:47 PM   #3
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I’d suggest a real battery switch that completely eliminates the chance of parasitic loads, or simply remove the negative terminal wiring. The battery(ies) will still discharge over time, but it’s MUCH less than it does with the parasitic loads.
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Old 07-07-2019, 06:07 PM   #4
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How low of voltage is too low? I’d say keep the batteries above 12.0V if possible and 11.8V in an emergency. There are many variables including temperature and state of rest that make it hard to know the state of charge of batteries while they are being used based on Voltage.

I too think your batteries need to be replaced. I just use and abuse my cheap wet cell batteries and replace them when they won’t provide a full night of furnace or fantastic fan use. My first set of Interstate batteries lasted only ten months for the same reasons as your batteries. I choose to replace them with a quality set of Golf Cart Batteries and 400W of solar. With these upgrades, my battery problems were solved. I can leave my Airstream in outside storage indefinitely. I can run anything I want all day and night and my batteries stay above 12.0V most of the time. I’ve abused these batteries with deep discharges to 11.8V many times in their 200 nights of dry camping and they still test and perform as new.

Replace your batteries. Add a real disconnect switch for use while storing your Airstream. Consider high quality deep cycle batteries. Consider solar if you intend to dry camp often. Keep the voltage above 11.8V under load.
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Old 07-08-2019, 12:03 AM   #5
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Thanks!

Yup, battery cut-offs are planned. There are two HEAVY red cables coming off the batteries. I suspect one goes to the inverter the other to the house so it should be easy to isolate the two. That way I can switch off the phantom parasite unless I actually need something in 110v.

My external solar panels did charge the batteries, as did the charger when plugged in to city power, the problem is the voltage dropped to 11.v (meter panel, I will calibrate to my VOM) overnight with very, very minimal load.

Tomorrow morning I'll pull the batteries, take them down to Interstate and try to get them exchanged.
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Old 07-08-2019, 01:15 AM   #6
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Interstate will hopefully replace the batteries. This Battery School site is a good source for info on RV battery care:

http://www.batteriesnorthwest.com/batteryschool.cfm

Generally speaking, voltage should be kept above ~12.2 volts [50%], in order not to affect the useful life of the batteries.

Good luck,

Peter
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Old 07-08-2019, 11:59 AM   #7
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Hi

Not mentioned so far - check the water levels in your batteries. You may find they are a bit low ....

No matter how you do it, monitoring battery charge state with voltage is a hassle. The little meters that read voltage and show a percent are lying to you most of the time If you rarely run off grid, voltage may be fine. If you *need* to know what's what, you might want to upgrade to a fancy shunt based monitor.

Why toss that in? If you are hassling with putting in a cutoff switch and *then* do the shunt it's sort of a double hassle. Doing them both at the same time is a bit easier.

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Old 07-08-2019, 12:10 PM   #8
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I know with my specific trailer that leaving the master disconnect in the on position allows .1 of an amp draw on my batteries. In that case in a little over a month my batteries are showing a fairly low battery level. Maybe enough to hinder much use of the jack stand. With master disconnect in the off position the draw is .01 of an amp, which is the draw from the propane detector.

With all the changes over the years with the position of the switch and the electronics your draw might be much different. But understand that your refrigerator, your thermostat on the wall, water heater, furnace just to name a few items can all be drawing small amounts of power even though their switches are in the off position. That's why the use of the master disconnect switch (or however it's labeled today), is important when your trailer is not in active use.


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Old 07-08-2019, 12:16 PM   #9
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What I don't think anyone told you is that while it might look like your batteries charged up, with solar or a charger, because they are shot they do not hold that charge. After a very short time the voltage drops significantly. Healthy batteries will stay at a full charge, 12.65, for a long time with just small parasitic loads. I second Peter, 12.2 is about 50%, and you should not let your batteries go below that, when measured as resting voltage, that is with no load and having rested for about 30 minutes after charging or discharging. Those wet cells need to be kept fully charged when not in use.
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Old 07-08-2019, 04:54 PM   #10
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Smile Interstate replaced the batteries for free

Thanks all.

Interstate just swapped out the batteries.

I confirmed that the inverter has its own 4gage wire leading from the batteries so that will be very easy to route it to a cut off switch of it's own. The house line is only an issue because the terminal at the end will have to be changed to a lug before installing it's cut off along with a shunt to use with a real battery monitor.

Thanks again.
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Old 07-08-2019, 05:40 PM   #11
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You dont need a seperate disconnect for the inverter, Connect one side of the disconnect to the positive terminal and both your positive wires to the other side of the disconnect. Or many peole prefer to put the disconnect on the negative terminal between the battery and chasis ground. There are several threads that debate the merits of each approach.
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Old 07-08-2019, 05:56 PM   #12
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Thanks for the update.

Happy Trails!

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Old 07-09-2019, 07:50 AM   #13
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Hi

If you *are* going to put in a shunt based monitor, they pretty much all go in the negative return to the battery. They need to be the *only* thing connected to that side of the battery. This immediately gets you into joining up the inverter and house cables (at least on the negative side).

The "keep it simple stupid" approach is to just put in a disconnect switch in the same negative return lead (as mentioned above). Yes there are some questions one might ask about doing this. It is in no way different than the "standard practice" of pulling the negative lead when working on a battery bank. You get the battery out of the circuit. It will not drain when out of the circuit.

The Victron BMV-712 is pretty well regarded here on the forum. There are other models out there and I'm sure they also do a good job. The 712 is set up to talk to your phone via Bluetooth. That's the way I use mine. I never look at the readout anymore.

If you want to get a bit more fancy, the Blue Sea 7000 series solenoids let you mount a remote switch to do the disconnect.

https://shop.pkys.com/Blue-Sea-7700-...2V_p_1691.html

They have the benefit of supplying an LED in the switch so the wife can ask "did you remember to disconnect the battery? The light is still on ..." as you lock things up in storage. That feature *has* been used in the real world

Lots of fun !!!

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Old 07-21-2019, 01:59 PM   #14
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The discussion about sundry and "phantom" battery draws reminds me of my dismay when I walk through my home after sundown - the number of "indicator lights" glowing! I am always trying to find ways to minimize my power consumption yet in order to function properly, some things must be left in the idle position so that they power up properly. I am amazed when viewing the electric meter knowing that there are no appliances running that the thing is spinning merrily away. Just thinking out loud here but you may want to check your LED indicator lights to see which items require stand by and which ones don't - I would shut down anything that doesn't require a stand by setting which would help diminish battery drain.
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Old 07-21-2019, 09:21 PM   #15
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Fwiw, having to avoid going to zero was the main reason I switched to lithium ion batteries. We just went dry camping and last exactly 3 days and we ran the inverter at night to run my daughter's sound machine.

We definitely hit the limit as we were packing up as everything cut off and I had to do the hitch manually.

We could have conserved more but didn't.

If you can pull it, I would consider lithium if you want to have that extra capacity without the fear of going all the way down in voltage.
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Old 07-21-2019, 10:52 PM   #16
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Thumbs up Further follow up

Just got back from 5 days of boondocking. Only used the solar panels. Plenty of power even for the inverter to run our Nesspressso.

Clearly my original batteries were fried.

Thanks all
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Old 07-22-2019, 07:23 AM   #17
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Quote:
Originally Posted by Alreddawg19 View Post
Fwiw, having to avoid going to zero was the main reason I switched to lithium ion batteries. We just went dry camping and last exactly 3 days and we ran the inverter at night to run my daughter's sound machine.

We definitely hit the limit as we were packing up as everything cut off and I had to do the hitch manually.

We could have conserved more but didn't.

If you can pull it, I would consider lithium if you want to have that extra capacity without the fear of going all the way down in voltage.
Hi

One minor point:

It's really the BMS on the lithiums that allows you to "run to zero". It cuts off the circuit before that happens. The newer "drop in" lithiums have the BMS built in. Some older units had an external BMS setup that went along with them. Once upon a time people did DIY systems with no BMS. They often found that was a poor decision ....

Bob
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Old 07-22-2019, 08:32 AM   #18
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Originally Posted by uncle_bob View Post
Hi

One minor point:

It's really the BMS on the lithiums that allows you to "run to zero". It cuts off the circuit before that happens. The newer "drop in" lithiums have the BMS built in. Some older units had an external BMS setup that went along with them. Once upon a time people did DIY systems with no BMS. They often found that was a poor decision ....

Bob
Thanks!

My understanding is that this is still more capacity than AGM or Lead Acid in terms of allowing for more complete discharge (per the spec as you mentioned), is that not correct?
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Old 07-22-2019, 09:51 AM   #19
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Quote:
Originally Posted by SagaCapt View Post
Just got back from 5 days of boondocking. Only used the solar panels. Plenty of power even for the inverter to run our Nesspressso.

Clearly my original batteries were fried.

Thanks all
Thanks for posting about the outcome of your battery experience. It's all too typical for new units to have bad batteries on delivery to the customer, but glad to see that's all it was and you got warranty replacements from Interstate.
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Old 07-22-2019, 01:24 PM   #20
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The National Electrical Code (NEC) indicates that 114 volts is the lowest acceptable operating voltage.

That’s an excellent standard to reach for. But in the real world, 108 volts may be the lowest operating voltage that can squeak you past potential damage. If it’s any lower than that, your compressor motor can give up the ghost.

http://rvlife.com/low-voltage-in-your-rv/
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