Fridge-How long on house batteries

[booster]

The video doesn't state the type and capacity of the Travato, but research indicates it has two 100a AGM batteries. They also allow their batteries to drop to 25%, which I understand shortens the life of the batteries.

I, too have a 100W solar panel and two batteries, but my compressor refrigerator is twice the size and my batteries are flooded wet cell.

Based on my test (with an empty fridge), I have about 10 hours on battery power if I run the refrigerator, ceiling fan and a couple of LED lights (assuming I don't want to drop below 50%). Yes, the solar panels can keep up during the day, but they can't re-charge the batteries while the fridge is running - they don't make enough power.

This means that I have to start the engine or generator each morning before the panels get enough sun to help. Works out fine because I use that opportunity to run the coffeemaker and blow dryer. Once the batteries are charged in the morning, I'm good for another 24 hours.

I'm mentioning this because I want to encourage the OP to perform their own tests before taking a video at face value.

The whole thing with taking care of AGM batteries has been discussed here many times, and a lot of the information seems to be contradicting the 50% rule for discharge limits on them. What we have found is that it appears the life vs discharge depth charts have been misinterpreted over the years and then the incorrect conclusions made got transformed into a hard and fast rule that would have folks believe that their batteries will die very quickly if taken below 50% SOC. If you look at the actual energy in/energy out life, which is what really matters, you lose around 10% of life by going to 20% SOC on every cycle not the 50% to immediate doom we often hear. If only 1/2 of your cycles went to 20% and the rest at 50% you would lose only 5% lift. For those that need more capacity, this can be an important thing, as you get 60% more capacity when you go to 20% and could mean not needing more batteries.

What will shorten the life of your AGMs is having all the charge cycles not get the batteries totally full, which takes a long time to do. Getting the last 20-30% into your batteries can take over 6 hours of charging at absorption, and many charging sources don't do a very good job of it. Most manufacturers want a 100% charge every 7-10 charge cycles or every few weeks if used sporadically, it appears, and that should help preserve the batteries. The first symptoms of problems will be that the batteries will "walk down", losing capacity over time and charge cycles.

How are you checking your SOC? If you are using a monitor, most of them need to get to fully charge status regularly, also, to calibrate the SOC and AH readings back to zero, as they will drift over time due to charge efficiency inconsistencies.

You seem to have come up with a schedule and procedure to be able to cover your needs and stay above 50% very well, but I don't think it will put a full charge on the batteries and be cycling them in the 50-80% range. Making sure you get a full, long, charge cycle periodically will help you batteries last longer by a significant amount. Of course, some folks have decided that they will accept the shorter battery life for the convenience of not having to get a full charge regularly (both with wet and AGM batteries) and there certainly can be a case made for that decision also.

 

[Saldar]

...folks believe that their batteries will die very quickly if taken below 50% SOC. If you look at the actual energy in/energy out life, which is what really matters, you lose around 10% of life by going to 20% SOC on every cycle not the 50% to immediate doom we often hear. If only 1/2 of your cycles went to 20% and the rest at 50% you would lose only 5% lift. For those that need more capacity, this can be an important thing, as you get 60% more capacity when you go to 20% and could mean not needing more batteries.

Booster, I read all your posts because they are so helpful. I'm not clear on what you mean above, and I'd like to understand. It sounds like mixing 20%/50% use would give longer life than 20% use only. What am I missing?

 

[mojoman]

When you get to the hotel, put a bag of ice in the fridge, it will cycle on less. I observed this when I put frozen water bottles in my 12v compressor fridge.

 

[booster]

Booster, I read all your posts because they are so helpful. I'm not clear on what you mean above, and I'd like to understand. It sounds like mixing 20%/50% use would give longer life than 20% use only. What am I missing?

It can get confusing because many of us use two very similar terms, that sound nearly the same, but mean the opposite of each other Some use or understand only one or the other, so it gets them turned around, I fear.

I think what you are questioning is what appears to say discharging 20% and 50% about the same amount of times in a cycle and how that could be better for the batteries than discharging 20% all the time. If meant as being this way, it would not make sense.

What I was referring to in the post was "state of charge" (SOC) of the battery, which is how much power is left in the battery. I think what you are referring to would be "state of discharge" and also called "% discharged". I generally prefer state of charge as it matches what a battery monitor gives you, and most of the battery manufacturers charts.

The fact that the point used very often as a reference point is the same for both at 50% doesn't help the clarity

So what I was saying is that if have your discharge cycles going to 20% left in the battery half the time and going to 50% left in the battery the other half, the number of rated discharge cycles will be the average of what it is at each of the points. Higher than if all were at 20% left and lower than at 50% left. Most people look at the charts and tell you that you get 1/2 the "life" at 20% compared to not going below 50%, but the chart is based on recharge cycles, not how much energy went in and out of the battery. If you look at the amount of energy in and out, it is only about 10% different.

In the real world, that means you have 60% more energy that you can use before you recharge, if you go to 20% left in the battery. For instance, you could stay offgrid 3 days instead of 2 before needing to recharge. It could also mean you could get by on two batteries instead of 3 or 4 for some.

There are a couple of threads on the forum that go way into how it all works out in detail. If you are a glutton for punishment, there is lots of good information there, but it might make you head spin and eyes roll

The other downside is that if you tell 98% of folks that you think the 50% rule really isn't valid, they will certainly get on you about it, as that rule has been used as the gold standard for long time!

 

[wincrasher]

The video doesn't state the type and capacity of the Travato, but research indicates it has two 100a AGM batteries. They also allow their batteries to drop to 25%, which I understand shortens the life of the batteries.

I, too have a 100W solar panel and two batteries, but my compressor refrigerator is twice the size and my batteries are flooded wet cell.

Based on my test (with an empty fridge), I have about 10 hours on battery power if I run the refrigerator, ceiling fan and a couple of LED lights (assuming I don't want to drop below 50%). Yes, the solar panels can keep up during the day, but they can't re-charge the batteries while the fridge is running - they don't make enough power.

This means that I have to start the engine or generator each morning before the panels get enough sun to help. Works out fine because I use that opportunity to run the coffeemaker and blow dryer. Once the batteries are charged in the morning, I'm good for another 24 hours.

I'm mentioning this because I want to encourage the OP to perform their own tests before taking a video at face value.

You have a much larger (and thirstier) refrigerator than found in a Travato. These "tests" are highly subjective considering we don't really know how much solar they are actually getting (i.e. intensity of the sun). I've found the 100watt panel can keep up with the refer just fine during the day, but as you said, offers zero benefit at night. So essentially, it's still a death spiral if you don't run the engine. Each hour of engine idling should get you 40-45 amps back into the batteries, even with the stock alternator.

 

[booster]

You have a much larger (and thirstier) refrigerator than found in a Travato. These "tests" are highly subjective considering we don't really know how much solar they are actually getting (i.e. intensity of the sun). I've found the 100watt panel can keep up with the refer just fine during the day, but as you said, offers zero benefit at night. So essentially, it's still a death spiral if you don't run the engine. Each hour of engine idling should get you 40-45 amps back into the batteries, even with the stock alternator.

I agree, and would add that if the batteries are in the top 20% of state of charge, you probably won't see the 40-45 amp hours back into the batteries as they won't accept power that fast when near full. At 70% and below you will get that, and likely even more with two AGMs and stock alternator.

 

[Saldar]

I
What I was referring to in the post was "state of charge" (SOC) of the battery, which is how much power is left in the battery. I think what you are referring to would be "state of discharge" and also called "% discharged". I generally prefer state of charge as it matches what a battery monitor gives you, and most of the battery manufacturers charts.

You are right about my misapprehension. I was thinking of percent discharge rather than SOC. Thanks for straightening me out. I dig your post now!

 

[Saldar]

I agree, and would add that if the batteries are in the top 20% of state of charge, you probably won't see the 40-45 amp hours back into the batteries as they won't accept power that fast when near full. At 70% and below you will get that, and likely even more with two AGMs and stock alternator.

I'm almost there....
....Do you mean if your batteries are nearly full (80% SOC) they won't accept 45Ah from the alternator
and
...at 30% SOC (low) they will start to accept lots of amps from the alternator? Or do you mean at 70% SOC (pretty full) they will start to charge fast?

I noticed that when we drive home 2.5 h on a cloudy day after camping plugged in, my batteries aren't very charged, and low acceptance may explain it.
My method of checking was to look at the charge at 3 am after coming home. With the fridge still running: 12.4V. I was surprised that it wasn't higher. (To calibrate: if I leave my Travato plugged in for 3 days (fridge off), then unplug and turn off the 12v loads at 9pm, and check at 3am I see 12.9V that quickly turns to 12.8 with lights on. I think that represents fully charged. I don't have a shunt, but I hope the 2 (mostly identical) voltage displays the Travato comes with (Zamp and One Place) are at least precise. I check at night to get around seeing the solar charging voltage.)

 

[booster]

I'm almost there....
....Do you mean if your batteries are nearly full (80% SOC) they won't accept 45Ah from the alternator
and
...at 30% SOC (low) they will start to accept lots of amps from the alternator? Or do you mean at 70% SOC (pretty full) they will start to charge fast?

I noticed that when we drive home 2.5 h on a cloudy day after camping plugged in, my batteries aren't very charged, and low acceptance may explain it.
My method of checking was to look at the charge at 3 am after coming home. With the fridge still running: 12.4V. I was surprised that it wasn't higher. (To calibrate: if I leave my Travato plugged in for 3 days (fridge off), then unplug and turn off the 12v loads at 9pm, and check at 3am I see 12.9V that quickly turns to 12.8 with lights on. I think that represents fully charged. I don't have a shunt, but I hope the 2 (mostly identical) voltage displays the Travato comes with (Zamp and One Place) are at least precise. I check at night to get around seeing the solar charging voltage.)

Near empty batteries will accept a lot of amps, nearly full batteries hardly any. On our AGM bank of 440ah, we are talking about the difference between 280 amps and 2 amps, so huge difference.

Voltage is a bit tough to tell much about state of charge, but your numbers are pretty low. To tell for sure, you would have to shut everything off for an hour or so, and then read the voltage, as loads can really mess things up.

That is a little strange. After being plugged in overnight and then a drive besides, I would expect to see the batteries full, or very close to it.

One of the things that solar does poorly sometimes is that it can mess up the shore charger charging. If the solar is holding the voltage up about full battery voltage, maybe 12.7-12.8v, a lot of chargers will go right to float and you won't get a good charge at the 13.2-13.5v of float, especially overnight. We have that happen on our Magnum, even, so I always check the voltage after plugging in to see that it went to absorption voltage of 14.4v. I have the solar absorption set at 14.3v so the bigger, more consistent, Magnum takes over the charging and running the van.

I would also be suspect if you alternator is charging the batteries when you drive. Most vehicles charge at 14.4-14.6v and when you first stop you will see over 14v if the batteries are full and have surface charge on them. The voltage will relatively quickly drop to the full battery voltage of around 12.7v.

You may want to just keep a record of what voltages you are seeing at various times, especially during transition times like starting/stopping driving, plugging/unplugging etc, as well as watch if and how long the shore charger stays in absorption. I think for that it will likely get fairly easy to see what is going on.

 

[avanti]

Near empty batteries will accept a lot of amps, nearly full batteries hardly any.

When I get confused about things electrical, I find it useful to picture a pneumatic system. The analogy is almost perfect:

volts = pressure
amps = air volume
charge source = air pump
battery = air tank
wires = pipes
switches = valves
amp/hours = how long you can draw a given volume of air from a tank

So, if you use a pump of a certain size to pressurize a tank, at first the tank will take lots of air easily (since the tank is almost empty). The longer you pump, the higher the pressure in the tank so the harder (and slower) it is to force more air into the tank. Bigger tanks will take more total air, and more easily (at first). You can determine the volume of air in the tank by measuring the pressure, but you must do so with high precision.

 

[Phoebe3]

Were your 10 hours from full to 50% in the dark (overnight) or did they include time when solar contributed?

I might be able to do this test overnight, if I checked the voltage before the sun comes up (when solar charging changes the voltage).

Thanks for the good information.

Sorry for the delayed response - working takes a big chunk of my day.

I should have specified that I get 10 hours at night. And remember that my fridge is bigger and I have flooded batteries, which I understand are faster to discharge and slower to take a charge than AGMs. Also note that in addition to the fridge, I'm running a fan and a couple of lights.

Works out OK because if I'm fully charged when we go to bed, in the morning we can run the generator for a little bit, which allows coffeemaker and blowdryer to function. Then once we are charged, the solar panels take care of the fridge during the day.

While the video was fairly representative, they "fudged" the numbers a bit. For example, they state that the fridge has been on 12v for four days when it had been three full days and 9 hours (8am Friday to 5pm Monday) at which time the battery was at 25% and wasn't going to get any more power that night. Since the batteries dropped 25% per day, they would have dropped to zero that night. That is, by the end of a full four days, they would have had zero battery.

Most people who are boondocking use more than just the refrigerator and they are starting with the batteries fully charged at 5pm, not 8am, so there won't be any solar help that first night.

Therefore, I would guess (without testing) that if you arrived at your destination with fully charged batteries and the Travato setup (AGMs and small fridge), that you could go a maximum of 48 hours before needing to run the engine or generator. Less if you used your batteries for other applications as well.

My setup eats batteries even faster.

Hope this helps. I bow to those with more experience...

 

[mojoman]

When we go into a hotel, I have an aux 75AH AGM battery I switch to to run the fridge 12v compressor (7CF), the battery has its own 40watt solar panel. It allows me to shut down/isolate the lithium bank. We stayed in a resort in Vegas, 100F+ for 4 days. The battery never got below 50%. The van was parked in the sun so the panel was working well.
By putting 4 frozen 24oz water bottles from the freezer into the fridge helped, It took 2 days for the bottles to thaw upon which I replaced them more frozen ones from our room's freezer.

 

[BBQ-ClassB]

When I get confused about things electrical, I find it useful to picture a pneumatic system. The analogy is almost perfect:

volts = pressure
amps = air volume
charge source = air pump
battery = air tank
wires = pipes
switches = valves
amp/hours = how long you can draw a given volume of air from a tank

So, if you use a pump of a certain size to pressurize a tank, at first the tank will take lots of air easily (since the tank is almost empty). The longer you pump, the higher the pressure in the tank so the harder (and slower) it is to force more air into the tank. Bigger tanks will take more total air, and more easily (at first). You can determine the volume of air in the tank by measuring the pressure, but you must do so with high precision.

Good analogy

 

[booster]

At the discharge rates commonly seen in a class B, which would at least around the 20 hr rating amp hours, you should see no difference between wet cells and AGMs, as long as both were full when you started and rated the same. The only time AGMs handle discharge better is at the very much higher discharge rates.

The AGMs will charge faster in almost all cases, as you say.

How are you determining your battery state of charge %?

 

[Phoebe3]

The GoPower solar display shows the voltage for each of the battery packs. Then I'm using this chart to determine the percent of power left:

https://www.emarineinc.com/Batteries-Maintenance-101

I know, I know,...just enough to be dangerous...

 

[booster]

The GoPower solar display shows the voltage for each of the battery packs. Then I'm using this chart to determine the percent of power left:

https://www.emarineinc.com/Batteries-Maintenance-101

I know, I know,...just enough to be dangerous...

Not great information in that article, especially on the charging end of it as the totally ignored the hold time at full voltage to get full, and didn't mention the amps taken by the battery at all.

The voltage chart is probably not too bad, but voltage isn't a great determiner of state of charge. The batteries have to be without any load for about an hour or so before reading the voltage. If the solar is running output at all it will influence the voltage reading.

As we recommend to nearly everyone, investing in a good battery monitor is probably the best thing you can do for your RV power system, as you will absolutely be able to tell if you batteries are full, or more likely not, after charging, and how much power you have actually used accurately.

 

[Phoebe3]

Do you have a recommendation for brand of monitor?

 

[booster]

Do you have a recommendation for brand of monitor?

By far the most folks use the Trimetric version. It is a good unit, and and has been around quite a while. A little learning curve to get optimally programmed and learning what really matters, but invaluable information for anyone who wants to take good care of their batteries as well as possible.

 

[eric1514]

I installed Trimetric in my van and although my electrical capacity and needs are modest compared to most here, I still find it invaluable. In fact I would argue, the smaller your battery bank is, the more useful the monitor is.

 

[Saldar]

One of the things that solar does poorly sometimes is that it can mess up the shore charger charging. If the solar is holding the voltage up about full battery voltage, maybe 12.7-12.8v, a lot of chargers will go right to float and you won't get a good charge at the 13.2-13.5v of float, especially overnight. We have that happen on our Magnum, even, so I always check the voltage after plugging in to see that it went to absorption voltage of 14.4v. I have the solar absorption set at 14.3v so the bigger, more consistent, Magnum takes over the charging and running the van.

If there is a solar/line charger interaction I'd sure like to get a grip on it. I believe the issue would be endemic to all Travatos because they share the same stock chargers, so your thoughts might help others. Or maybe the story is obvious to everyone else.

The 3 charging stage voltages (last is float) for the Travato equipment:
For the Zamp solar charger: 10-14 V, 14.4 V, 13.6 V
For the PD line charger ------: 14.4 V, 13.8 V, 13.3 V

It appears the Zamp might dominate the PD, by making it think its 2nd stage trigger voltage (14.4) has been reached. Do you suspect the PD might not do bulk charging sometimes even if it was needed?

I read 14.4 V often during sunny days. Can the Zamp be misleading by deciding to put out 14.4 V before the battery has reached it's physical absorption mode?

I have the pendant to control the PD. Is the amperage supplied by the PD different in the 1st and 2nd stages? If the first stage supplies higher amperage, is it dangerous to force that phase if the battery is in absorption?