Some thoughts on Battery Management

TabRookie

We are just back from a three-month maiden voyage in our 2020 Tab 400.  That might sound more impressive/crazy than it is.  We had a three-day drive to our summer vacation cottage where the Tab remained parked for the duration of the stay.  My teenage daughter happily used it as her personal space for most of our stay.  The Tab did not move again until we started the trip back a few days ago. 

The start of our trip three months ago was not that great and I talked about it in previous post.  Our problems, though, were almost entirely self-inflicted due to inexperience.  So, for the return trip we paid more attention to how we used our power. 

We planned to drive about seven hours a day.  Open campgrounds are scarce in these parts this time of year so we would be boondocking and needed to conserve battery power as much as possible.  We would run the refrigerator on battery while moving and switch over to propane when we stopped for the night.  We also ditched anything that needed electricity other than phone/computer chargers.  We hoped that the power drawn from my truck combined with the power generated from the solar panels would be enough to keep our batteries in good shape.  This was especially important considering we were transporting precious frozen cargo…salt cod and partridgeberries (ask a Newfoundlander). 

So how did it go?  Somewhat successful. 

(I am not sure I am reading the Victron Connect app correctly so I would be happy if someone would correct me where I am wrong).

Day 1 gave us mostly clear skies and we were able to generate a 100Wh yield.  We started the day with a full charge so I did not expect to generate too much power.  When we stopped for the night the control panel in the Tab showed we still had a full charge but I'm skeptical.  The app says I had a max battery charge of 14.38V and a min of 12.89V.

Day 2 was another sunny day.  The max/min voltage in the battery was 14.58V and 11.41V.  The solar panels also generated 260Wh of power.  The control panel still said we were in good shape and the touch test of the cargo seemed to confirm that. 

Day 3 is where things went sideways.  It was a terrible day for weather.  Pouring rain, a snowstorm and a much longer drive time meant we used up more battery juice than we had hoped.  The Panels only generated 50Wh due to a break in the skies near the end of the day and the truck could not keep up with the drain.  When we stopped for the night, the batteries only had an 11.64V charge remaining.  We switched to propane for the night and hoped for the best the next morning.

Day 4 was only a two-hour drive.  We would have finished it the night before but the weather turned nasty (more snow) and I was very tired so we stopped.  When we tried to flip the refrigerator over to battery, we discovered the previous day’s drain had been too much and it would not run.  Since it was such a short drive, we just turned it off knowing the cargo would not be affected.  By the time we got home, the batteries had recovered enough that the refrigerator was back to normal. 

So fellow campers…are we doing this thing right?  Your insight is most appreciated. 

GFC

Why do you run the fridge on battery?  We did a 5 week trip from 9/5 to 10/11, driving about every other day, and ran our fridge on gas the entire time, even while driving -- it worked great.  A canister of propane will run the fridge for about 2 weeks.

pthomas745

The day 1 numbers look ok.  The 14.38V would be a "charging" voltage, and the min of 12.89 seems ok.  Day 2 min voltage of 11.41 is not good, but there may be a good reason. Day 3, of course, was a "wash" in the rain.

If you have a 3 way fridge, you would conserve considerable power by using propane instead of 12v on the overnight stops.  You would even help your vehicle charge your battery by turning off the fridge for a couple of hours while driving.  The cooled down fridge is a great cooler.  (But, salt cod, I get it.  I just read a nice book about Cod by Mark Kurlansky). 

The other issues with the "low" or "high" readings is the whole issue of a "rested battery".  Trying to take battery readings while something in the trailer is running, or the solar panel is providing a charge, will just lead you astray.  Voltage readings will always be low or high in those cases.  If the fridge had kicked on when the Victron made that measurement, the 11.41 or even the 11.64 readings could have been very misleading. 

VictoriaP

GFC said:

Why do you run the fridge on battery?  We did a 5 week trip from 9/5 to 10/11, driving about every other day, and ran our fridge on gas the entire time, even while driving -- it worked great.  A canister of propane will run the fridge for about 2 weeks.

Propane use while in transit is considered a potential fire hazard. It’s also illegal on certain roads, tunnels, and bridges, and for safety’s sake you have to remember to turn it off every time you get gas.

I’ve seen way too many burnt out trailers and motorhomes in over 30 years of RV ownership, not worth the risk.

TabRookie

@GFC for safety reasons we do not feel comfortable running propane while moving.  Not worth the risk.

@pthomas745 we do have the 3 way fridge and we did exactly as you suggested...switched to propane for the nights.  

Denny16

I agree, running propane systems whilst you are towing, is a bad idea, against the law in some states, and not a good practice.  I have seen too many burned rigs that caught fire as a result of having propane running.
cheers

TerryHutchinson

The 2 way electric compressor refrigerator uses less power than the 3 way in 12 volt mode.  This is just how things are, so a long day driving with dark skys and the 3 way on battery power may very well deplete the battery.  I don't know your tow vehicle (maybe I missed it above) but modern vehicles are very stingy with alternator power and cannot be counted on to supply much juice to a trailer house battery.  There are some ways to trick the vehicle to power up the alternator more, but it depends on the specific TV you have.  Some TVs are even set up with dual alternators for this purpose.  If you are going to boondock and you cannot be certain that your solar panel will be getting much sun energy, you should consider a dual house battery arrangement - it will give you a much larger power drain buffer and let you go longer without reliable recharge. The stock OE battery is pretty bare bones.  For a couple hundred bucks you can get a pair of 6 volt wet cell golf cart batteries that would triple your available power . . . and, of course, there are more expensive options that will do even better than that.

VictoriaP

TerryHutchinson said:

 If you are going to boondock and you cannot be certain that your solar panel will be getting much sun energy, you should consider a dual house battery arrangement - it will give you a much larger power drain buffer and let you go longer without reliable recharge. The stock OE battery is pretty bare bones.  For a couple hundred bucks you can get a pair of 6 volt wet cell golf cart batteries that would triple your available power . . . and, of course, there are more expensive options that will do even better than that.

The OP has a 2020 Tab 400, which already has a dual battery setup, since that comes stock.

bergger

I have been on a few long drives with our 2021 400, 12 hours being the longest.  I find that using the 12v power to cool the fridge is probably not worth it.  I'll use it for the first 2-4 hours of the trip, monitoring the battery with the app, then turn it off for the next leg of the trip to allow the solar to charge the battery.  Generally the fridge is insulated enough to not use the 12v anyway and your food will be just fine when you get to your destination and turn on the gas.  Also we take a few freezer packs and put them in the fridge to help keep temps down when we travel .  Then refreeze them over night and put them in again when we travel.  You can also freeze a few drinks and do the same thing.  Never had any issues with the fridge getting too hot and our batteries have done fine.  

Marceline

I think that the 3way fridge isn't really optimal for transporting precious frozen cargo. For next year you might want to consider getting a 12v compressor ice chest that you can use as a dedicated freezer. As someone else mentioned, you could use it to cycle through ice packs to use to keep the T@B fridge cool in transit instead of putting the 3way fridge in 12v mode.  

Denny16

Victoria, I think Terry was referring to a dual 12VDC house battery setup (common on larger boats and RVs.  The TaB400 has two 6-volt batteries which are wired in series to get one 12-volt power source, so acts as a single battery, but a lift more efficiently.  

A dual house battery setup, normally consists of two separate 12VDC (or 24/48-volt) battery banks (each bank could be more than one battery in a bank like the TaB400), wired to a A/B dual battery switch, which allows selecting bank A, bank B, or Both.  Vehicle/vessel starting battery is separate, so house power drain does not effect engine starting ability.
cheere

VictoriaP

Denny16 said:

Victoria, I think Terry was referring to a dual 12VDC house battery setup (common on larger boats and RVs.  The TaB400 has two 6-volt batteries which are wired in series to get one 12-volt power source, so acts as a single battery, but a lift more efficiently.  

A dual house battery setup, normally consists of two separate 12VDC (or 24/48-volt) battery banks (each bank could be more than one battery in a bank like the TaB400), wired to a A/B dual battery switch, which allows selecting bank A, bank B, or Both.  Vehicle/vessel starting battery is separate, so house power drain does not effect engine starting ability.
cheere

I’m aware of dual 12v setups. But he suggests replacing a single stock battery with a pair of 6v in his post...for the Tab 400, only the 2018 and perhaps a handful of 2019 units came with a single battery. Later models like the thread starter’s 2020 come with two already, and changing an existing pair of 6v that does not appear to be failing isn’t going to change a thing for their situation.

@TabRookie The cheapest and simplest solution to your problem is doing something along the lines of what @bergger suggests: run the fridge intermittently while in transit. As most people end up stopping for gas or bathroom/stretch breaks every two hours or so, one possibility is to switch the fridge on at one rest stop and off at the next. Barring extreme heat conditions, the fridge can handle being off for a few hours if everything is already chilled. Ice packs or frozen water bottles will certainly help. I do suggest using a fridge thermometer if you do this.
The next easiest alternative is likely a 12v cooler, as was also suggested. It’s more of a nuisance in that you have to move the food, but it is a viable solution in the $500 or so range for the size you’d need.

Also relatively cheap if you don’t have to pay for labor is installing a DC to DC charger. There are posts on here that should turn up with a quick search, detailing how these work. I think there was one within the last week or so. The units themselves aren’t pricey, but if you have to pay for labor, you may end up in the same range as a decent (not high end) 12v cooler. But, your trailer batteries would be better charged while in transit.

Beyond that, you have generators, additional solar panels, or upping your battery capacity. At least one 400 owner here is up to four batteries now. The really high end solution would be 4 lithiums and and extra solar panel or two. 

TabRookie

Thanks everyone for the comments.  I think the performance we got was close to expectations.  The point of my thread was to see if this was what others have been experiencing.  And that seems to be the case.  

Under normal circumstances we would probably go from one campground to the next on a long trip like this.  That way we would be on shore power for the night and replenish the batteries.   Next summer we probably won't be bringing back so much frozen goods so the need to stay frozen won't be an issue.  

Denny16

Thanks Victoria, I see that at the end of Terry’s post,  but at the beginning he also suggested,  “If you are going to boondock and you cannot be certain that your solar panel will be getting much sun energy, you should consider a dual house battery arrangement” which is the statement I was referring to, and you on the two 6-volt battery setup.  Sorry about the confusion.
cheers