Help figuring out if another 100ah lifepod battery will help me or not?

DIY
1

I overpanelled to about 1100W which has helped a lot. I have been fine most weeks through the winter period with that and the dc-dc charger on my when I do a weekly drive to stock up on food for the week.

I also bought a low voltage disconnect so I could squeeze the last drops out of my lithium battery, not leaving unused power on the table.

90% of the time all the above allow me to sail through quite comfortably so long as there is only one or two really cloudy days however lately there have been longer runs of 4+ days where solar is pathetic.

Initially when I got them I was thinking there would never be a scenario where buying another battery would be better than just more panels but some days the solar is just so bad I think you would need a whole field or solar to make a dent. Some days as poor as 0.2A average! vs nearly 40A which is the max for my MPPT on good days and clipping the rest.

The battery is only 100ah and I am wondering if another 100ah will help or is it just a waste of time because I am rarely seeing surplus charge/clipping on the battery/mppt. Though I am wondering does it not even need to be often? I know if there is just one decent solar day that the battery can be filled within only a couple of hours and the mppt flashing full. If I had 200ah and it was able to fill both would it be like having savings in the bank, where you don’t have to spend it all within days, and it is just there ready to use for the longer periods of cloudy days, which could be a couple of weeks away?

I am not sure about that though because wouldn’t it drain it little by little on those days where you were not in a surplus, which is most days? Then again though, if I am managing to skate by just about with 100ah that other 100ah would not be being tapped much would it and the majority would still be available for the longer runs of poor weather?

Batteries are the most expensive thing so I don’t want to buy another and find out it didn’t even help me.

Also this battery is 1 year old now but had only done about 40 cycles from what I recall last time I checked on the app and the manufacturer told me I am good linking a brand new battery with this one up to 100 cycles on the current one without issue but I know eventually it will go over that so want to decide whether to get that extra battery or not before it goes over the accepted limit, if I am to get another.

Having written it out now I think it should shouldn’t it? So long as there is a good solar day only now and then allowing a surplus to top off both? it doesn’t have to be clipping every day or regularly for the second battery to be viable? just the odd day when they can both get pumped up and then the surplus is there in reserve for when it is needed?

2

I would get another battery. You need 7 days autonomy to manage in-between the weekly trips. I would assume the trip would then top them off if solar was absolutely rubbish for over half of it. So not much need for more solar (its a disease i tell you :upside_down_face: - )

Adding to a lifpo4 is not as fussy as lead acid after 40 cycles. So agreed with the supplier you are golden there.

Bu i hear the eternal struggle balancing solar battery charging and load.

2 Likes
3

Thanks, well actually the driving would not top off both, it is about 30 minutes there and back on a 60A charger, but it only outputs 40 I believe from other reports. Whatever it is it doesn’t fully charge the battery. I see it more of a boost, albeit a good one, to the solar, with solar doing most of the work.

Yes 7 days autonomy but solar isn’t in the pits all 7 days. It is in the pits some days, and many more recently but there can be mediocre days which tide me over, which they mostly have, at only 1-5A averages but it is those many days below 1 where it really starts to get tight!

As per my previous musings I wonder if £300 worth of more solar would work out better than another battery, which is what it would cost. :thinking: Much more work involved in that route, and don’t know if my single MPPT would handle it. I have the space but na I think it would be a waste to take up such space only for these winter months. 2x 445W panels has been a nice addition and battery would probably be a better choice at this point.

The question is where the power will come from to charge them both!

The other option though, is to just run the van on idle for 30 minutes or so to give a quick boost when really bottoming out if it was not time to take another drive naturally. I know it isn’t good for the engine to do that too much but if it is only now and then don’t think it is a problem.

It’s actually been pretty rare that it goes this long with many poor days back to back but when it does it is disruptive and due to several storms back to back. That is what makes me wonder if it is worth the outlay of another battery rather than just a cheeky idle van dc charger boost for the couple of times it happens.

4

Hmm. If its not that often then a cheeky charge like that would be ok.

And a IP65 12v or phoenix smart for a bit of a wall charge not an option?
The IP65 has on more than one occasion saved me from a flat van battery too so it has other uses.

1 Like
5

No, fully off-grid, for power at least. :slight_smile:

Other route is to lower consumption. This laptop takes up 3x the power that the tablet/laptop hybrid I had used to use, probably mostly because the screen is almost 2x the size. The other one broke though. I have been given an android tablet which charges by usb I just haven’t bothered to look into getting it going but that would slice a good chunk of daily power as computer use is the main constant along with heating at this time of year.

6

The OP still has not been answered yet though, only the other options discussed, if you only need a day or two short large bursts to top off the 2x batteries? then the energy remains stored for when it is wanted.

7

We can only pitch ideas or add second vote to an idea. Maybe add some thoughts that OP hasn’t come up with yet.

Agreed. Consume less or make and store more.

8

Just a suggestion of course but while camping off grid, and too many consecutive cloudy days to rely on solar, I purchased a small 2000 watt generator to keep the house batteries charged.

Using a vehicle’s alternator to charge external batteries is hard on it and will eventually cause premature failure.

1 Like
9

True. It is easier to replace a little generator than a whole vehicle.

10

TBH, replacing an alternator with double or triple its output will put you back only fraction of the cost of a proper generator. For about 200 imperial units you could get a 160a or even 300a alternator which will put just a bit more strain on your motor, designed for over 80hp, where a 2000w generator is a whole different set-up with a much smaller motor and a separate gas tank, finicky bits and old carbs etc.

I do question if its actually worth it.

1 Like
11

As a further thought though it is not totally necessary to charge your battery to full all the time. Its ok to go more than 1 week or 2 without ‘absorption’ or balancing.
So even you get close and it still takes you through its possible the next week things on the solar side will pick and and fill up anyway.

12

To be clear the 2000 watt Yamaha generator I use only supplies power to a Victron battery charger which in turn charges the RV’s house batteries. I monitor the charger’s progress with the VictronConnect app.

The generator is only used as an emergency power supply when there’s insufficient solar which for me is not very often. It’s only a backup power source. The added benefit is there’s zero wear and tear or modification to my vehicle.

13

Perhaps it’s envy on my part, :slight_smile: but I was never able to justify the price of a generator over the cost or difficulty of replacing my alternator or just it’s rectifier and brushes.

I will say, my vehicle has a redundant alternator setup so I will always have power. I also carry spares and it’s a 30 min job to fix.

But it would appear that a motor designed for 1m distance units and a generator, especially one that size is designed for hobby use. My understanding and experience is that they break down seasonally and need extensive maintenance, where the consolidation of mechanical efforts would imply that a single “better alternator” or even a redundant system would better fit the application and use case.

Especially considering the price and space required to carry an extra bit of kit.

After over 1.2m km, I’ve had to replace the alternator components once

15

It is a quesiton of how often of course, isn’t it? As stated in the OP I had only had to idle the van a couple of times, probably 2 or 3 at the time of writing, so that is not going to put any kind of dent in the engine longevity. I drive week to week very little, with only 1 weekly shopping run on average, except for an exceptional case, so weighing it up, think about people who are using their van for working. They must be idling at traffic lights far more in total even week by week than I am idling just to charge the leisure battery in the winter months.

In the past few days though things have gotten far worse and it is really bugging me as I am having to run the engine every single day. Thick blankets or cloud or mist one after another. Even so this doesn’t justify getting a generator. I would instead buy another battery and also look to the energy saving techniques. I did a calculation and if I ran a 5V, 2A device to run internet/my computer that would save me 70% of energy. When I use the computer about 8 hours a day, it is an irony that during winter one uses the most electricity due to being inside more yet energy is scarcest, then I figured that the saving on energy for about a week would also be the equivalent of another 100Ah battery.

What I noticed the other day on the one sunny day in as long as I can remember, to answer my own question I posed earlier, is that it provided a full charge to the 100Ah battery within only a couple of hours and so then that energy was just being wasted. So just one day like that and a larger battery bank could top them up within the day.

When I first got the panels I laughed to myself and thought that more solar is always going to be better than more batteries but now I see that in this super heavy cloud days the solar just can’t make anything worthwhile to provide energy so batteries do make more sense, to bank what you can while the sun shines.

Playing devil’s advocate, as I am of the same mind as you, that an alternator is not worth it for just a couple of days per year, but isn’t the main concern breaking the engine, not just the alternator? I researched the issue a while ago, with much information online already about iding engines and possible damage, and the main issue mentioned was if, I don’t remember the proper term, the engine itself gets some kind of coating inside it which would be very hard and expensive to fix. However, as mentioned above, I doubt the couple of times would make any significant difference in that regard? Even so I do feel bad idling too much and it is just a nuisance when it gets to be every day, which is has been this week.

Don’t understand what this means? Are you just saying I can discharge the battery deeply? If so that is what I have been doing. I ran it right down to 12V this week, which is where the low voltage disconnect should kick in, which it has before when I tested it when I got it, it was probably just because it was borderline and went back up a couple of decimals points soon after. This gives a little more juice but I notice once I am into the 12s then there is barely anything left and it will quickly deplete. I am aware of the flat voltage curve of lithium batteries, just stating I see it in action!

16

February seems to be the worst, even worse than December and January for the pounding storms left and right, even though the days are longer. I remember it being the same last year, with the fog enveloping the skies for what seemed like weeks.

The former two it was colder, but clearer skies when cold, so the solar could charge the batteries, to charge the heater and other stuff!

Last night was sad. I had no heat, very little energy for the laptop and when I did run it the internet decided not to work so I just read for a while and went to bed. It is about thinking whether it is such a hardship that I want to invest in other measures. I know in a couple of weeks the solar will suddenly bounce back and it will feel like a distant memory.

Even so it is about planning for next year, as this was an issue just the same the year previous, and as I mentioned, I don’t want to miss the window for the battery paralleling with the cycles getting too high.

Off-gridding is always about weighing up these things and managing your limited resources. Same with water when it was drought in summer last year for a very long stretch.

One more battery and the energy saving tech seem both like prudent options and not too lavish, considering I only have 100Ah currently.

21

So, no, i dont know your make and model, but idling the engine for an hour is usually no problem at all. People in europe dont like to see it because of the “clean” image, but its not going to damage your engine

the thing with the batteries are kind of like a water tank you carry around all day, it needs to be big enough so you dont have torefill it every day, but small and light enough to carry around.

So I have 6 150ah batteries.
in summer, I need almost no capacity, so i just roate them with a threeway switch. one day Ill use this bank, next week Ill use the other.

And in winter, I keep all six of them on so I can stand autonomously for easily 2 weeks if Im a bit conservative.

Buying a 2000 gulden expensive device, to use for maybe max 4 months in European winter doesn’t cut the stuff for me. It really is a use case thing. now a battery of 2k puts you right in that same spot.

More solar in winter : well obviously yes, but efficiency is more important than size. Bigger is not always better, the idea being better bang for your buck is better than bigger with less bang. make sense?

So the alternator thing is obviously the cheapest and most efficient method to get that bang for your buck. in a van it takes no more space, you can sit in the front and idle your engine for an hour no problem (unless you’re in Germany, dont do that in Germany; Verboten!)

The equalisation thing means that your batteries charge to 100% state of charge. What happens when the battery equalises, is that the cells are “balanced” this is an important step with lithium, if this doesn’t happen often enough “drift” occurs. Thats going to happen anyway in a system used every day.

That about sums it up, but if you need more information, lets talk about a specific path youd like to go.

And no, I wont edit this out, its important that this is visible.

(And no, I just have a sneaky suspicion and started looking at “sloppy” user names)

1 Like
27

I should explain drift a bit better.

Drift Happens when multiple physical devices are calculating for the same effective equation. shunts are little bars of metal that can help calculate power in vs power out.

Shunts have a pre-set, lets say 150a capacity and charge efficiency, you can set amperage loss over wire gauge and a bunch of other stuff.

Unless that was precisely calculated and exactly measured and set, loss occurs then over time.

So if you have just one measuring device your system will only read that and perfect.

But if you dont equalise over time…the state of charge will “drift” and not be correct.

So by equalising, the battery can go back to its true 100% soc and that pushes the shunt logic back into a more correct perspective.

1 Like