2018 T@B 400 solar charging problem - need HELP

PamandJohnUpNorth2 · December 2019

We are on the road in the midst of an extended boondocking trip (Big Bend Texas)

2018 T@B 400, 2- 6 volt AGM batteries with a Victron MPPT 75/15 controller.

Our batteries are not achieving float stage despite ample sun. I want to check settings first, does anyone know the voltages for equalization, and absorption?

Voltage settings and/or suggestions are much appreciated.

DenisP · December 2019

Attached are screenshots from my settings and from a post on the Harris batteries setting.

Image: https://us.v-cdn.net/5021717/uploads/editor/07/fpptt7y9k9qe.jpeg

Image: https://us.v-cdn.net/5021717/uploads/editor/yb/o2lr36nyyin0.jpeg

PamandJohnUpNorth2 · December 2019

@DenisP Thank you for the speedy response. I am set within a .1 volt on both of those so that must not be the issue.
Next suspects i guess are the batteries and controller itself.

Cbusguy · December 2019

Do you have any idea on your consumption?

Do you use an inverter?

I would hate to thing two year old batterys would be dead.

rfuss928 · December 2019

Your batteries may not reach float stage while boondocking. The absorption stage is purposely long and doesn't start until bulk current drops below 1~2amps. In most cases, running between 60 and 90% SOC will make the most of available power and keep your batteries in good condition. Don't expect to reach 100% (float) daily and be comfortable working anywhere in the 50-100% SOC band. Check SOC just before sunrise and again just before sunset for a few days and determine your pattern and trend.

Have fun.

pthomas745 · December 2019

Wouldn't the issue of having to measure a "rested" battery be the point here? Or is that what @rfuss928 is saying?

Sharon_is_SAM · December 2019

I think if you are actively charging and using your battery, you can’t really check it in a resting state. I think the idea is to accept that you can safely operate within the 50-90% range - who needs 100% charge!

PamandJohnUpNorth2 · December 2019

@cbsguy @rfuss928 @pthomas745 Thanks for helping me puzzle through this. For sure I am hoping the batteries arent toast after two years. Perhaps as @rfuss928 suggested i am needlessly anxious about the battery status but what is wierd is that the battery does not enter absorption phase either. Typical readings on the Victron app show a daily minimum of 12.13 volts more and max of 13.85. I thought absorption would start around 13.4 or thereabouts.

We have a rarely used factory installed inverter. Switched on and off per use. I did have a draw down to 11.84 volts after use of hair dryer last week but the day following showed a minimum 12.4 and a maximum 13.5

As I have been looking at power usage, I realized I would be advised to turn off the water pump when water is not in use because it appears the pump uses 4 amps? The other uses of power are the 12 volt fridge 24/7, minimal interior lighting, and the alde on propane about 12 hours a day. ( I'm adding a BMV-712 to my project list!). As suggested, in the AM ,get a resting SOC and do the same again in the evening, and repeat for a couple days to get a trend of the true SOC.

Ever hopeful that I might see absorption or float tomorrow!

pthomas745 · December 2019

Any time you use anything in the trailer, the SOC will drop. When you turn that "thing" off, the SOC will climb back up. I bet when you used that dryer, and saw the 11.84....if you watched for a few minutes the SOC would have climbed back to a much more ordinary level.

With 2 6v batteries, I figure you have roughly 100 amp hours to use. I'll say you used a 700 watt dryer for 6 minutes. 700 watts divided by 12 amps means the dryer would use about 58 amps per hour. Or, "roughly" an amp per minute. That six amps of hair drying cost you 6 amps, or only 6 percent, of your total available amp hours. Yes, the Victron showed a SOC of 11.84......but that is not an accurate reading of your battery. That "mininum" of 12.4 is probably closer to reality.

The pump only uses power when it is pumping. Just having the switch on does not cause any drain on your battery. The pump on my 320 only uses about 2 amps per hour when pumping.......and I would be out of water well before an hour was up if I ran it continously! I leave mine on at the campsite, and have a checklist item to turn it off before towing.

You have a lot of amps to play with. The fridge is probably the biggest user. The Alde does not use much at all.

Sharon_is_SAM · December 2019

@PamandJohnUpNorth2, what battery monitor are you using?

PamandJohnUpNorth2 · December 2019

@Sharon_is_SAM I am getting the voltage readings from the Victron MPPT 75/15 using the android app "Victron Connect" .

Perhaps as @pthomas745 and @rfuss928 and you have suggested I need to be less OCD about momentary battery voltage levels, put the smartphone app down and see what happens. Solar, and watts = amps x volts is a new learning curve for me -thanks to all for the info you have shared.

I guess worst that can happen is we have to re-enlist our tenting skills, and we do have a generator if we have to use it.

b407driver · December 2019

If you're using the VictronConnect app, do you use the history page (bar graph) to monitor these trends? If you could screenshot the week in question, it would be helpful to post it so we can see the trends.

FWIW, other than summer desert sun, I'd expect not to be able to boondock indefinitely with typical two-person usage (i.e. every day the battery SOC will be a bit lower than the day before). My last trip in Sept I made it about a week before I had to move the trailer for a 'perfect' angle down lower where there was more sun (1 person only). Everyone's mileage varies.

pthomas745 · December 2019

@PamandJohnUpNorth2 There is a detailed 400 guide in the Manuals section. On Page 53, there is a spreadsheet that details the amp usage of practically everything in the trailer.

https://tab-rv.vanillacommunity.com/discussion/6371/t-b-owners-manuals#latest

It is called T@B 400 Resource Guide.

rfuss928 · December 2019

My solar is primarily to support refrigeration (12v Norcold). Lights, water and heat are a nice consequential convenience. My sense of SOC is most influenced by the observed effect of the refrig cycling on battery voltage. When my batteries are fresh, fully charged (float) there is very little effect on measured V (generally less than 0.1v). But at lower SOC the V difference increases up to ~1.0v . This is when I better be planning on charging. The system V would also be low (~12.0v) at that point.

A conveniently visible Volt (and Amp) monitor lets you glance and see the effects of different loads at different SOC when you flip a switch or hear an appliance cycle. You will quickly develop a sense of normal for your patterns. The rigor of at rest protocols are for absolute measurements that can be compared to others measurements. Your practical at rest V measurement may be with some low "phantom" draw still present. If that is always constant for your observations you will adjust your expectations compared to "standards". In a 200ah system a one amp draw is mostly inconsequential.

Don't obsess.

Have fun!

Bob

PamandJohnUpNorth2 · December 2019

Well Good News! (at least for now). Today I the opportunity to connect to 120V and use a small Norco Genius Battery Charger to recharge the battery directly. It took a while to get to "full charge" and afterwards turned the solar back on and the controller took the batteries through absorption and back to float before the sun set. At least this gives me a good start for the next week of boondocking.
So I've learned from the group I probably need to temper my expectations, especially with winter sun angles and shorter days and while being aware of usages dont obsess about voltages every hour. I'm going to try and "chill out" for at least the next 5 days and see what happens and provide an update then, Thanks to all for the reference info, experience with solar, and encouragement! I'll provide a future update

,
@b407driver above are the last 5 days thru 12/15 sunset. I am looking at those calculations on page 53 of the Resource Guide now. Thanks!

Cbusguy · December 2019

A simple fix would be to augment your trailer mounted panels with a couple of flexible panels on the ground so you can move them around as needed to get in the best position to gather sun light.

ChanW · December 2019

@Cbusguy has a good point.

Turning and tilting your 400 throughout the day, to keep the roof panel at an optimum angle for the low sun, just doesn't seem practical. (Although that might be why Nucamp included those handles!)

PamandJohnUpNorth2 · December 2019

Thanks for the external panel suggestion. I will keep that in mind. Isnt it funny how after you have a travel trailer and purchased an endless number of additional things there is always just one more thing you need. 😆

2018 T@B 400 solar charging problem - need HELP

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