Battery Discharges Quickly

DanL

Hello Fellow Campers.

I am new to camping and I don’t know a lot about batteries, but I feel like my battery is discharging too quickly.    I am currently on a camping trip and following is what I observed last night......

6:50 pm - 11.91v - 41% - I know I should not let the battery go below 50%, but I can’t seem to keep up with the charging.

7:00 pm - started charging with generator at 29.1 Amp, 373 watts.

8:00 pm - stopped charging and battery read 12.47v or 87%.

9:20 pm - battery read 12.23v or 63%.    I did this reading because I understand from previous discussions that the battery will read higher than actual right after a charge.

9:00 am - read battery at 11.94v or 44%.   

So the battery discharged from 12.23v to 11.94v overnight.     All I had running overnight was the fridge at a setting of 2.5, water pump briefly to brush teeth, bathroom light briefly, and any parasitic drain.  I feel like the battery is discharging too quickly.

Does this seem normal based on other’s experiences?    Am I just expecting too much from my battery?

I am using a Victron BMV-712 battery monitor to do the above readings.
I have a Tab 400 with the 2 x 6v batteries.

Thanks!
Dan.

Bayliss

@DanL, I do not have a T@B 400 (I have a 320S with a three-way fridge), but if your refrigerator can operate on propane, use that instead of the battery.  You can run it on electricity when camped at a campground with hook-ups.  The refrigerator will discharge the battery pretty fast, but I would expect that it would have depleted a lot more power from the battery if the refrigerator was the culprit.

Sharon_is_SAM

You are reading your battery while under load from the frig running, so it may read lower.  You should be able to read the amps consumed.  Does it correlate?  Besides the frig, you have other parasitic drain - Jensen, TV,  LPG/CO detector, USB outlets etc.  Are you able to charge it up to 100% before the generator cut off time?  Did you start with it completely charged to 100%?

VictoriaP

A battery can take as much as 12 hours to reflect its actual voltage after charging. Your reading at 9:20 of 12.23v was likely inaccurate on the high side, as it was taken little more than an hour after charging.

Additionally, an hour of generator use isn’t sufficient to really charge a single depleted battery, let alone the 2 large batteries on your 400.  

webers3

Don't know about 400 but on 320 running the fridge on battery will discharge it in no time, not recommended.

elbereth

You’re probably nowhere near a full charge.  Those 2 batteries in the 400 have a 220 Ah capacity, according to nuCamp.  Your hour of charging at 29 A would give you basically 29 Ah (less actually because of the Peukert effect and charge efficiency), so about 13% of your capacity.  So it also means your BMV-712 needs recalibrating (which I find happens frequently, especially if the charged voltage and tail current settings “trick” it into thinking it’s fully charged when it’s not.)

Two things you can do - plug it in when you get home and just leave it for several days to let the converter give you a full charge (and/or use a separate battery charger).  

Then go into your BMV settings and hit the “synchronize” button in the settings so it knows you’re at a full charge.  That should set 100% to 100%.  While you’re there, make sure the battery capacity is set correctly as well.  This is easiest in the Victron Connect app, but you can follow the steps in the manual to do it directly on the unit as well.

If you have the stock 2-way fridge (rather than the 3 way that comes with the 320S) it really shouldn’t eat up too much battery.  We have the same on our CS-S and can get through a weekend easily without depleting the battery.

pthomas745

All good advice.

What output are you seeing from your panels?  Are you sure they are charging?

dCliffhanger

I see many quoting the % of batter capacity left. Where are you getting this number? I've got a T@B 320s and I've got LEDs that indicate Full, 3/4, 1/2, 1/4 I think and dead.  The Bluetooth app to my solar tells me the amount of watts the panels have produced and the battery voltage.  That's it.

VictoriaP

dCliffhanger said:

I see many quoting the % of batter capacity left. Where are you getting this number? I've got a T@B 320s and I've got LEDs that indicate Full, 3/4, 1/2, 1/4 I think and dead.  The Bluetooth app to my solar tells me the amount of watts the panels have produced and the battery voltage.  That's it.

Older models had SeeLevel sensors which provide a readout. The 2019 and 2020 have KIB sensors, which only give you the approximation you’ve noticed. The indicators are actually F 2/3 1/3 E. And for battery purposes, it’s worthless.

JEB

dCliffhanger said:

I see many quoting the % of batter capacity left. Where are you getting this number? I've got a T@B 320s and I've got LEDs that indicate Full, 3/4, 1/2, 1/4 I think and dead.  The Bluetooth app to my solar tells me the amount of watts the panels have produced and the battery voltage.  That's it.

He’s using a BMV-712 to monitor his battery. It provides significantly more data on battery SOC than the solar controller does.

Cbusguy

As others have pointed out you only added approx 30 amp hours to a 250 amp hour battery very roughly about a 10 percent charge.

There are many unanswered questions....age of the battery's, what does the victron show as the current draw from the battery?   That is the big question.

@dCliffhanger there are charts that circulate on the internet that give rough approximations on remaining battery capacity.    The issue is they don't take into account age, temperature, or any history of battery.    In my book it is a slight step up from the provided 4 light panel.    The only way to know for sure is an inline amp meter 

pthomas745

You can get a good idea of your battery State Of Charge with the age old method of multimeter on a rested battery. 

Sharon_is_SAM

@pthomas745, I don’t think he has solar.  I think that was optional with the 2018 400.

@webers3 - the 2018 400 comes with a 2 way that is pretty efficient.

rfuss928

The refrig probably draws ~50 watts when running.  Ambient temps make a big difference on how much it runs but if you assume 50% then it would use about 300 watt-hours overnight.  His charging cycle only added about 350 watt-hours so the input and usage pretty well match.

Assuming the battery had rested enough for the overnight SOC comparison, 19% of 220 Ah was used - about 500wh.  Or, 50% more than was added with the generator.

All of these calculations are in the general ball park of what DanL observed given the imprecise methods and possible calibration errors mentioned.

I think the system is acting normally and as expected. 

Increasing charging time to 1-1/2 or 2 hours would probably better match usage patterns described.  The batteries were accepting almost a 30 amp charge.  Generator current and watts out will decrease significantly as the batteries approach full charge.

Awca12a

My gut is that you drew down the batteries doing something unexpected and haven't allowed it to come back to full charge.  The alternative is that you have a phantom draw somewhere that is outside of "normal".  A quick test is to go to page 53 of the Resource Guide and use your BMV-712 to compare your T@B actual to the column called "400 AMPS" on Page #53.    The manual can be found on the 1st post of this thread.
https://tab-rv.vanillacommunity.com/discussion/8650/unofficial-nucamp-t-b400-resource-guide-finalized#latest

Your resting BMV draw should show  0.35 amps per line #2 of the chart where it says "Always Running" with everything turned off.   Then, cycle-on the things you use each day and compare your draw numbers to the chart.  If your numbers aren't way off then it's possible you have a bad battery cell and the battery isn't holding charge.  Testing that will be a bear so first go through the process of looking at your BMV history for total battery energy drawn & absorbed from one day to the next.    Post what you find and perhaps the helpful forum members can provide additional insight.

davel4wa

How far did you tow your trailer and does your tow vehicle have a charge line? Perhaps the battery was discharged more than you thought after towing to your camp. 
As far as putting an ammeter in series with your battery, with your Victron system, that is actually what you already have. The Victron utilizes a shunt in series with the battery set to measure current. That's what an ammeter does.

rfuss928

So many of these power management discussions could be quickly resolved if amperage measurements were available.

IMO  If you are going to install or carry equipment to provide portable power, a basic measurement tool is a AC/DC Amp Clamp.  To measure Power (Watts) you need Amps and Volts.

These are available for as little as ~$50.  Many include a multi-meter and probes.

The current measurement is non-contact.  You simply "clamp" one wire from the device (solar, generator, lights, fan, refrig........) inside the jaws and the current is measured.

It is very difficult to trouble shoot relying just on the processed output of a control or monitoring device.  Something like this lets you probe every wire and device with no trace.  Understanding Amps is understanding where the Power is moving.  Voltage is mostly a tell tale effect.

Here is a link to the meter pictured.  It is not a recommendation, just an example I found quickly:

https://www.amazon.com/dp/B00X3RS59U/ref=sspa_dk_detail_0?psc=1&pd_rd_i=B00X3RS59U&pd_rd_w=cOz0E&pf_rd_p=8a8f3917-7900-4ce8-ad90-adf0d53c0985&pd_rd_wg=ORsDb&pf_rd_r=PXNWK2SW366DE625Z021&pd_rd_r=892947a2-656d-48a5-9717-62b93125dfa8

I have worked on electrical systems forever and my amp-clamp is used at least as often as my voltmeter.  I think some of the folks in this and similar discussions would learn to make good use of this tool.

Have fun & keep learning!

jkjenn

The key is to really have a grasp on what power you are consuming. I believe someone created a list of the power draw for various items and the phantom drain for the 400 so that could easily be plugged into a spreadsheet similar to mine for the 320. The clamp meters are ha dy, but proba ly not necessary on this case.

2 AGM 6v batteries can take a while to charge. If it were me, I would charge it with a smart charger to 100% and then reset the BMV 712 to calibrate. I would then. Then, next time you are out, pay attention to how much power you are using. Remember, the SOC, not the voltage is what you should rely on when you have the Victron. The voltage, as SAM said, shows your load.

JEB

rfuss928 said:

The refrig probably draws ~50 watts when running.  Ambient temps make a big difference on how much it runs but if you assume 50% then it would use about 300 watt-hours overnight.  His charging cycle only added about 350 watt-hours so the input and usage pretty well match.

Assuming the battery had rested enough for the overnight SOC comparison, 19% of 220 Ah was used - about 500wh.  Or, 50% more than was added with the generator.

All of these calculations are in the general ball park of what DanL observed given the imprecise methods and possible calibration errors mentioned.

I think the system is acting normally and as expected. 

Increasing charging time to 1-1/2 or 2 hours would probably better match usage patterns described.  The batteries were accepting almost a 30 amp charge.  Generator current and watts out will decrease significantly as the batteries approach full charge.

Your estimate of the amp draw of the Norcold NB 751 sounds reasonable.  The best test I’ve seen on this refrigerator can be found here.  https://www.buildagreenrv.com/design-and-build-information-for-camper-vans/installing-galley/measuring-refrigerator-electricity-use/  The conclusion in that test was that the fridge uses about 42 amp-hours (568 watt-hours) per day on the 3 setting at an ambient temp around 80 degrees.  It wouldn’t take long to materially impact the batteries without an external charging source.  And, unfortunately, the WFCO converter is not the best battery charger because it tends to take awhile to enter absorption mode and tends to exit too early for fast charging.  So, hooking up a generator for a short time (I’m assuming here that the generator was not hooked up directly to the battery bank but instead was being used as substitute shore power) wouldn’t charge up the battery as much as you would think.  Most of the time generator time was probably wasted by the converter limping along in bulk mode at an anemic 13.6 volts. Solar controllers are actually better for fast, short bursts of charging.

Awca12a

jkjenn said:

The key is to really have a grasp on what power you are consuming. I believe someone created a list of the power draw for various items and the phantom drain for the 400 so that could easily be plugged into a spreadsheet similar to mine for the 320. The clamp meters are ha dy, but proba ly not necessary on this case.

2 AGM 6v batteries can take a while to charge. If it were me, I would charge it with a smart charger to 100% and then reset the BMV 712 to calibrate. I would then. Then, next time you are out, pay attention to how much power you are using. Remember, the SOC, not the voltage is what you should rely on when you have the Victron. The voltage, as SAM said, shows your load.

You can find the draw table in the Resource Guide.
You can use your BMV-712 to compare your T@B actual to the column called "400 AMPS" 

Page 53 of the Resource Guide which can be found at
https://drive.google.com/file/d/1CTxMp8mzJ_tvvVb9FjmXF63E5WXZCO-2/view

Or use the full thread here:
https://tab-rv.vanillacommunity.com/discussion/8650/unofficial-nucamp-t-b400-resource-guide-finalized#latest

rfuss928

JEB

The generator was sending ~30A - 373 watts somewhere (must be ~12V).  It sort of makes sense it went to the battery.  The big battery bank was ~50% and could easily accept that rate and the battery SOC showed about the right gain for the generator watt hours also.

BTW  I've seen my 25A WFCO come right up to rated output on a depleted 150 AH AGM pair.  I agree that it rarely goes into absorption mode.

DanL

Thanks for all the great comments and advice.   Questions about batteries always seem to stir up lots of comments.

Sorry I haven’t responded to any comments since I wrote the original post.   I was camping with unreliable internet.   I’ll try to answer some of the questions and provide additional information.

The fridge in the Tab 400 that I have only operates on electricity.     I wish Nucamp would have installed a fridge where you have the option between battery and propane power.    Has anyone out there ever tried to change the fridge?    Any idea if this is even possible?    I assume Nucamp did not rough in a propane line to the fridge area.

I only ran the generator for one hour in the example because I got back to camp late and only had an hour left.     The provincial campgrounds allow 2 hours in the morning and 2 hours in the evening.    Although running the generator 4 hours a day or running it every day is not a good way to make friends.

The batteries are brand new.   This was only my 3rd time using the trailer.

I did not start the trip with 100% charge.    I live in a condo and the storage facility where I leave the trailer does not have a plug in.    I charge it as much as possible with the generator in the storage facility, but it would take a long time to get to 100% off the generator.

The current draw with the fridge off is 0.2 amps.
The current draw when the fridge switches on is 5.0 amps.

The outside temperature was 75 during the day and 55 at night.

My tow vehicle has a charge line.    It delivers 8.7 amps / 103 watts while driving.   Not a lot, but helps a little.

Based on all the comments and feedback, I am thinking that my battery is performing normally.     Perhaps my expectations were just too high.   Once I understand the limits, I can plan around them.

Another question.     I live in British Columbia and our provincially owned campgrounds do not have electric hook-ups.    I really want to start camping and exploring in the US.    Do state owned campgrounds have electrical hook-ups?

Thanks!
Dan.

Sharon_is_SAM

Dan, thanks for the update.  I would say most State parks have electric hook ups.  It really varies, so, of course check out their websites before you reserve.  

Just a word of caution, although AGM batteries are great, low maintenance items, best practice is to always fully charged prior to storage.  If you can find somewhere to plug in a smart charger compatible with your battery before storing and charge it fully, you would be able start your trip with a full battery.  Good luck!

VictoriaP

DanL said:

Another question.     I live in British Columbia and our provincially owned campgrounds do not have electric hook-ups.    I really want to start camping and exploring in the US.    Do state owned campgrounds have electrical hook-ups?

Thanks!
Dan.

State parks here in Washington differ wildly from each other. Some may offer full hookups including sewer, some electric/water, some electric only, some no hookups at all...and some may offer a mix of these depending on where you are in the park. And different states offer different amenities. California, for example, doesn’t seem to offer sewer hookups at any state parks. So unfortunately there’s no blanket answer for you on that score.

Addressing a couple other things:

NuCamp does offer a 3 way fridge on the 2019 and 2020 Tab 400, but you sacrifice the closet area for that. I would imagine retrofitting a 3 way would be pretty pricey. My understanding is that the 2 way is fairly efficient on battery overall, but to use it that way all the time, you have to have a way to recharge efficiently as well. 

You might also consider whether or not solar would be helpful in your situation. It’s tough to get enough sun in the northwest, but anything it added would be better than nothing, and unlike the generator there’s no noise limitation. As far as charging in your home area goes, do you have a friend or family member that can host the trailer overnight before a trip and offer you a power outlet to get to a full charge? Or can you occasionally use a full hookup park? Keeping the batteries in a constant discharged state can shorten their lifespan considerably, and the 400 does not use cheap batteries.

Marceline

Sharon_is_SAM said:

Dan, thanks for the update.  I would say most State parks have electric hook ups.  It really varies, so, of course check out their websites before you reserve.  

Maybe in some parts of the country, but California is a very big state and hardly any state parks here have hookups.

Marceline

DanL said:

I did not start the trip with 100% charge.    I live in a condo and the storage facility where I leave the trailer does not have a plug in.    I charge it as much as possible with the generator in the storage facility, but it would take a long time to get to 100% off the generator.

I think that this is the source of your problems. I am in a similar situation. I have the T@B CS which is a 2way fridge (no propane) and I have to keep it in a storage yard where there is no power. It takes an enormous amount of power to bring the refrigerator down from ambient temperature to refrigerate food. In practical terms, you need to find a way to plug in your trailer to get the fridge cold. A friend's house, a private campground with hookups, whatever. Once you have have the fridge cold, you will probably be able to maintain it with the batteries & generator. If I were in your shoes I would consider getting 200w of solar panels installed on the roof. I use a 100w panel and it just barely keeps up with my little fridge when I have full sun and long days.
If you have solar on the roof it will also charge and maintain your batteries while your trailer is in storage, which would eliminate the problem of starting out with a less-than-full charge. 

BrianZ

Here in Virginia, 27 of our 39 state parks have camping, while 23 offer campsites with water and electric hookups, and centralized dump station/restrooms/showers.  Some VA state parks are only for daytime use or only tent camping.
https://www.dcr.virginia.gov/state-parks/find-a-park

DanL

Thanks for all the comments on the battery charging and the state parks.   

A few few people have mentioned getting solar panels installed on the roof.   Certainly something to consider.  Would I need to order these from NuCamp or are there good aftermarket suppliers?    I’m a little worried about a dealer drilling into the roof to install solar panels in case it creates a leak.   Has anyone had a problem with leaks?

Thanks.  
Dan.  

rfuss928

DanL

If one of your goals is to minimize generator hours, you may be operating close to the optimum.

In the conditions you describe in the OP, you seem to manage on about 20-25% of battery capacity per day.  Batteries accept much higher charge rates when below ~80%  SOC and, as you observed, can recover a significant percent of capacity relatively quickly.  The last 10-20% (absorption charging) is much slower and can require hours to make relatively small increases in SOC.

Although not immediately intuitive, during generator powered camping trips you could probably manage quite efficiently keeping you batteries in the 50-80% SOC range.  This would minimize the required generator hours for recovering the consumed power.  It would be prudent to bring them up to 100% for a while whenever possible and definitely before storage for best battery life.

We all have different desires and priorities and finding what works best for you is part of the adventure.

Have fun!

Bob

Sharon_is_SAM

@DanL, not sure if you camp in the shade or sun, but roof mounted solar is best if you park in the sun.  Portable solar panels would allow you to park in the shade and move your panels into the sun and would not require any roof holes.  Then again, you can capture more charging going down the road and while in outside storage with roof mounted panels.  Just some food for thought.

Marceline

DanL said:

A few few people have mentioned getting solar panels installed on the roof.   Certainly something to consider.  Would I need to order these from NuCamp or are there good aftermarket suppliers?    I’m a little worried about a dealer drilling into the roof to install solar panels in case it creates a leak.   Has anyone had a problem with leaks?

Thanks.  
Dan.  

I'm kind of surprised that no one has chimed in by now, but if you search this forum for terms like "solar" and "install" you should find plenty of posts. Some people have done this job themselves, others have had dealers do it. I'm surprised that your dealer didn't suggest it, especially in view of your storage situation.