LifePO4 Battery - Infrequent Use.

Hi,

I have just started to convert my van. I have purchased a 435W house solar panel which will be fitted to the roof.

I plan to buy a LifePO4 battery and a Renogy DC DC charger with MPPT. I have read that the new version can handle up to 50V solar.

I am interested in the dual charger as I will be using my van infrequently, probably 10-12 times per year, between March and October. With the dual charger I will be able to keep the starter battery topped up with the trickle charge function.

My question is about the LifePO4 battery, I read it is not good to leave it at 100% charge, so between trips how would it be possible to keep the battery at a partial state of charge while also keeping the van battery fully charged via the trickle charger mode of the renogy? This is also a concern for the 5 months over winter where I would need to keep the LifePO4 at partial charge and the van battery trickled.

It would be a mistake to use a Renogy DC DC charger with a solar panel and a LiFePo4 battery. You should use a MPPT solar charge controller. Renogy makes solar charge controllers too such as the Rover MPPT.

Rickerman said:

I have just started to convert my van. I have purchased a 435W house solar panel which will be fitted to the roof.

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This is usually a bad idea. In high winds or even highway speeds, the wind can really knock your van around. If your van is one of the tall skinny ones, like Sprinter, then this is rather dangerous. Four 100W panels will handle winds much better than a single massive panel that acts like a wind sail.

Rickerman said:

I plan to buy a LifePO4 battery and a Renogy DC DC charger with MPPT.

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I hope I can convince you to save some money and not do what I did. Don’t buy Renogy. I started with a Renogy 30A Rover MPPT and 2000W inverter. Both had problems and had to be replaced. Neither covered by warranty. And customer service is extremely frustrating. They’re friendly but inept at reading comprehension and actually doing anything helpful.

Buy Victron if you can afford it. If cost is an issue, consider the high resale value you’ll get with Victron should you ever sell. Or buy Epever MPPT and Giandel inverter. By all means, don’t waste your money on Renogy. They look sexy and specs look good and price is nice but are dangerous to use. My Renogy MPPT nearly destroyed my brand new lifepo4 battery. The inverter was an energy hog at idle draw.

That Renogy DCDC converter with MPPT seems like it's designed for what you are doing, but all the specs I read say the solar input is limited to 25V which is pretty low unless you are using several of those 100W "12V" panels you find on amazon in parallel. Where did you see that it's rated at 50V? Also I agree the marketing of that product seems to based on pretty photos and check boxes rather than actual specs and clear photos of the inputs and output terminals. I think for that price you can get a separate solar charge controller like the Epever or HQST 40A MPPT controllers and you would be better off than this item.

I don't think it's a big deal to keep the Lifepo4 battery at 100% over the winter. I havent see data that this is actually a significant problem. You could also set the charge voltage of the lifepo4 to a low value like 14.0V to make sure it isn't getting stressed by sunny days in the winter.

The self discharge rate on the lithium batteries is around 2% a month. I leave my lithium batteries for 6-7 months with no issues.

Make sure to disconnect the batteries and if possible store them in a cool dry place.

If you are charging your batteries off of the alternator, consider using a folding solar panel with PWM charger while boondocking. I use a Zamp folding panel. The charger has a setting for lithium.

The advantage of the folding panel is that you can move it into a sunny area and park the van in the shade.

We just don’t recommend that lifepo4 batteries be stored at 100% capacity when not in use for a long period of time. It's fine if you use it occasionally. The lifepo4 battery comes with a BMS, but please note that the power supply should be cut off when the battery is not in use.

Your large panel is OK. Just use more metal brackets than used for smaller panels, minimum 6 brackets through bolted to the van roof.
Renogy products have atractice price but reliability and support from Renogy is questionable. In general combined units, DC to DC and MPPT, compromise the solar element of the unit. Seperate MPPT controller will perform much better.
The advantage of the more expensive Victron products is a long warranty, 5 years, ease of setting any charge profile and comprehensive performance data via phone app.
Being able to maintain the starter battery is east to implement with a battery 'master',
( despite the warning works with lithium)
The ideal charge voltage for lithium is 14.2 volts absorbtion and 13.5 volts float, this is low stress perameter. Whilst its easy to setup in Victron products many others have fixed or difficullt to adjust settings.

Over periods of non use I set my victron charger to low charge volts of 13.3 volts this results in aSOC around 70%.
Mike

I plan to bolt some unistrut to the roof of my van. These will be longer than the length of the panel and the panel will sit on top of them. I will then bolt 4 angle brackets to the panel and unistrut. Very similar to how this guy did it on his RV but I will bolt the unistrut instead of sticking them with 3M tape.


My panel turned up today but the glass is shattered, so waiting for a replacement.

I have not ordered the battery or MPPT yet though. I wanted to use the combined one as it would allow a cheaper way to also charge my leisure battery via the alternator. But the battery master looks like a good option but I would be worried it could drain my leisure battery over winter if I turn off charging. I am also looking into a second 20W solar panel and PWM controller just to keep the starter battery topped up.

I am going to have a 105AH fogstar battery. I will be running a 12v compressor fridge, some USB phone chargers, 12v lights, diesel heater, water pump and possibly 12v TV. With a 435W solar panel I'm not even sure if I need a DC to DC charger for the months I will be using it. (March -> October in UK).

Issue with LFP storage for several months is their self discharge rate is seldom well matched.

Self discharge rate ranges from 0.2% per month to 6 % per month depending on given cell and ambient temp they are stored at. Higher ambient storage temp increases self-discharge rate and increases the spread of variance on self discharge between cells.

The variance in self discharge rate between cells will misbalance cells over six or seven months to the point where when you try to fully charge battery there will be a BMS cell overvoltage trip that stops charging. BMS will eventually reset overvoltage trip by bleeding overvoltage cell and begin charging again. You can fix this with a long absorb level (14.2v) charge (BMS does not balance a cell until it is above 3.4v) but can take several hours, to more than 100 hours to rebalance cells well enough to achieve a full battery charge without a cell overvoltage trip by BMS.

Most self-contained 12v LFP battery BMS's only have a 50 mA to 100 mA balancing bleed current. A cell overvoltage trip during attempt at a full charge will start to occur when cell SoC misbalance gets to about 1% difference is SoC. For a 100 AH battery, 1% of capacity is 1 AH. 1 AH / 0.05 amp of balance bleed takes 20 hours to correct.

mikefitz said:

The advantage of the more expensive Victron products is a long warranty, 5 years, ease of setting any charge profile and comprehensive performance data via phone app.

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And you won’t need to use the warranty with Victron.

I’m extremely frustrated with Renogy’s customer service. They’re very nice but seem slow or unable to actually DO anything. Like read my messages when I give them the info they ask for. It’s like the “who’s on first” game.

Thanks for the comments. Regarding the Renogy Dual DC to DC charger with MPPT I also cannot find any specs online that states it can handle 50V solar input, only a few facebook posts and pictures confirming that the "New Version" does indeed support 50V solar, but you need the bluetooth module to enable the functionality.

I am now thinking about using a Victron SmartSolar 100 / 30 and Orion 12 12 - 18. This will work out more expensive but should be more reliable. I can then turn off charging via the bluetooth app when the van is not in use, or isolate them.

I still need to keep my starter battery topped up during winter and times it's not in use. I am thinking of a separate 30W solar panel and PWM controller. Or a battery master which uses the leisure battery to trickle charge the starter battery. Which method would be recommended? I am leaning towards the separate solar panel as it would not then take any charge from the LifePO4 battery.

I guess my final problem would be how to stop the Orion thinking the engine is running when it sees the voltage from the trickle charger and tries to charge the leisure battery (I guess it would be turned off so not an issue?)

Coming back to your question about using your van electrical system when not on vacation - IMHO, the answer is to use it.

Turn it on and keep it on. Turn on the refrigerator and put some items in it such as drinks, spices, or some foods that can serve in an emergency and have it run 24 x 365.

Consider to have some small amount of ventilation going to keep it from getting hot and musty in there.

Check on it once a week or so and see how it is working. This way you will know that it will work when you are ready to go on a trip.

You might even find that your family will use for misc things - when stationary.

Rickerman said:

Thanks for the comments. Regarding the Renogy Dual DC to DC charger with MPPT I also cannot find any specs online that states it can handle 50V solar input, only a few facebook posts and pictures confirming that the "New Version" does indeed support 50V solar, but you need the bluetooth module to enable the functionality.

I am now thinking about using a Victron SmartSolar 100 / 30 and Orion 12 12 - 18. This will work out more expensive but should be more reliable. I can then turn off charging via the bluetooth app when the van is not in use, or isolate them.

I still need to keep my starter battery topped up during winter and times it's not in use. I am thinking of a separate 30W solar panel and PWM controller. Or a battery master which uses the leisure battery to trickle charge the starter battery. Which method would be recommended? I am leaning towards the separate solar panel as it would not then take any charge from the LifePO4 battery.

I guess my final problem would be how to stop the Orion thinking the engine is running when it sees the voltage from the trickle charger and tries to charge the leisure battery (I guess it would be turned off so not an issue?

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Rickerman said:

Thanks for the comments. Regarding the Renogy Dual DC to DC charger with MPPT I also cannot find any specs online that states it can handle 50V solar input, only a few facebook posts and pictures confirming that the "New Version" does indeed support 50V solar, but you need the bluetooth module to enable the functionality.

I am now thinking about using a Victron SmartSolar 100 / 30 and Orion 12 12 - 18. This will work out more expensive but should be more reliable. I can then turn off charging via the bluetooth app when the van is not in use, or isolate them.

I still need to keep my starter battery topped up during winter and times it's not in use. I am thinking of a separate 30W solar panel and PWM controller. Or a battery master which uses the leisure battery to trickle charge the starter battery. Which method would be recommended? I am leaning towards the separate solar panel as it would not then take any charge from the LifePO4 battery.

I guess my final problem would be how to stop the Orion thinking the engine is running when it sees the voltage from the trickle charger and tries to charge the leisure battery (I guess it would be turned off so not an issue?)

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This is from the manual.

HarryN said:

Coming back to your question about using your van electrical system when not on vacation - IMHO, the answer is to use it.

Turn it on and keep it on. Turn on the refrigerator and put some items in it such as drinks, spices, or some foods that can serve in an emergency and have it run 24 x 365.

Consider to have some small amount of ventilation going to keep it from getting hot and musty in there.

Check on it once a week or so and see how it is working. This way you will know that it will work when you are ready to go on a trip.

You might even find that your family will use for misc things - when stationary.

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I could leave the fridge on, but I am not going to be storing my van at home. It will be in a locked compound. This is one reason why I want to make sure the starter batter is trickle charged when not in use, so I do not end up with a flat battery when I go to pick it up.

Rickerman said:

make sure the starter batter is trickle charged when not in use,

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The battery master maintaining charger, ( there are similar units on the market with slightly different designs), is in common use in UK motorhomes. With a battery master type unit the starter battery is limited to a lower value the the house battery, around 0.5 volts lower, and current limited to a few amps. With the default charge voltage and float of the Victron solar charger the starter battery maximum volts will be in the region of 12.8 volts, too low to trigger the Orion. ( The Orion trigger volts can be user set if needed, but it seems smart enough to deal with starter battery maintaining charge. If there are issues, then using an ignition active signal and the control inputs on the Orion, the Orion can be enabled only with ignition on )
I suggest the Victron Orion 12 12 30 rather than the 18 amp unit.
Unlike the simple Votronic unit I gave a link to earlier, a fully programmable device is available,


Leaving a high consumer on whilst the van is in storage is a risk, 450 watts in winter In the UK may not keep up with demand.

Mike

eemarty said:

I don't think it's a big deal to keep the Lifepo4 battery at 100% over the winter. I havent see data that this is actually a significant problem. You could also set the charge voltage of the lifepo4 to a low value like 14.0V to make sure it isn't getting stressed by sunny days in the winter.

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Depends on what you mean by a big deal. I speak from experience, storing for long periods of time at 100% will significantly reduce capacity compared to storing at 50%.

Just John said:

Depends on what you mean by a big deal. I speak from experience, storing for long periods of time at 100% will significantly reduce capacity compared to storing at 50%.

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I've heard the recommendations but I want to see the studies that quantify how much degradation there is.

eemarty said:

I've heard the recommendations but I want to see the studies that quantify how much degradation there is.

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From my limited understanding, the studies saying to not store at 100% for long are quite old and based upon older lithium chemistries. I’m not sure if there are newer studies based upon lifepo4. So far I haven’t heard of any but I’m no expert either.