MarkCX
Well-Known Member
Following on, how about just the Li from the solar with the just the B2B charger from the Li to the LA?
Worth comparing the inefficiencies of both methods.
Worth comparing the inefficiencies of both methods.
Dumping excess solar energy
- Thread starter MarkCX
- Start date
Kelpie
Well-Known Member
That depends. Let's say it's a 400Ah FLA bank, and you want a little LiFePO4 that's around 15% of that (60Ah). That's around £250 (Shop GWL | Lithium Battery 12V/60Ah (WB-LP12V60AH)) which is less than buying a pair of T-105 batteries.
You can also take a punt on the even cheaper offerings direct from China.
Having just the one Li battery appeals to me, because as I understand it it can greatly simplify the setup (BMS etc) and if you take a gamble on something from China you're not risking losing your whole bank, and a big wad of cash.
It probably does sound a bit too complicated, but it seems an interesting way to harness some of the major advantages of LiFePO4 without all the associated costs.
Poey50
Well-Known Member
That's old news, I'm afraid. These from Xuba are under £200 shipped to make a nominal 12 volt pack and with a capacity to match or exceed the usable capacity of 200ah of lead acid. 3.2v 120ah Li-ion Lithium Rechargeable Battery Lifepo4 Cell For Electric Car Solar System - Buy Lithium Ion Battery,Rechargeable Lithium Ion Battery,Lifepo4 Product on Alibaba.com
There are plenty of advantages to LFP but I think it will be their capacity to take up whatever charge you throw at them and their complete indifference to sitting around at partial charge which will make them a good complement to lead acid in the way that is being talked about. There will of course be inefficiencies in using LFP as a reservoir to top up lead acid to give them a longer life but so much less than the inefficiency of letting good photons go to waste. Of course they come with a lot of trouble and by the time you make a life-support system for them thoughts then turn to whether the whole of the house bank might just as well be LFP. But I think this complementary idea (which I first heard from GHA) has a lot going for it.
Last edited:
TernVI
Well-Known Member
This is true, but putting an actual £ figure on what a particular (ab)use pattern is costing is another matter.That significant damage is done by never or very rarely getting fully charged isn't a contentious view in the slightest, as a well respected US marine engineer has said - boat batteries don't die...they are murdered..
Your batteries are going to die. The only question is how quickly and whether expensive 'improvements' to the system are cost effective in longer battery life.
Plus how much do you want to run your life around getting six years out of a couple of hundred quids worth of batteries instead of 5?
TernVI
Well-Known Member
Let's read post 1 and see it's 125Ah. And post 36, actual consumption as little as 15Ah per day.
It seems the OP is aboard 24/7?
If there's not enough solar to charge fully this time of year, how's it going to look the other side of the equinox?
Either a lot more solar is needed, or a generator. You could bulk charge at C/5 for half an hour every morning, then the solar might have some chance of topping things up in November.
You could of course just motor around a circuit for half an hour with a high charging voltage, instead of buying a generator. Then you'd have hot water in the calorifier.
MarkCX
Well-Known Member
Not aboard 24/7 in the darker months, then it’s generator once a week if necessary.
GHA
Well-Known Member
Just showing a bit of interest into how they work and a bit of time learning isn't the worst thing to have to do, and will have a big payback in battery life if you spend much time onboard away from the mains.
William_H
Well-Known Member
The MPPT controller will take what voltage and best current from the solar panel to produce a voltage and current to suit the charge state of the batteries. When batteries are charged the charge current falls to a maintenance level. The solar power that is available is simply not used when not needed. OP wishes he could use that excess solar power for some good purpose like charging a lithium pack.
He needs to detect in some way that the panel is producing lots of power and that it is not needed for battery charging. Possibly a voltage detector on the solar panel output would indicate these conditions. Like a VSR set at about 18 volts the output of the VSR then could operate a relay to connect the lithium battery to the main battery for charging. That assuming the lithium battery can be charged from about 13.5 volts of main battery on maintenance charge. Or connect a lithium charge controller direct to the panels. However any of these actions will/may pull down the solar panel no/small load voltage turni9ng VSR off. So may take a lot of experimentation to get the set voltage for the VSR just right. Ultimately forget the whole idea and just charge your lithium pack when you need to. ol'will
He needs to detect in some way that the panel is producing lots of power and that it is not needed for battery charging. Possibly a voltage detector on the solar panel output would indicate these conditions. Like a VSR set at about 18 volts the output of the VSR then could operate a relay to connect the lithium battery to the main battery for charging. That assuming the lithium battery can be charged from about 13.5 volts of main battery on maintenance charge. Or connect a lithium charge controller direct to the panels. However any of these actions will/may pull down the solar panel no/small load voltage turni9ng VSR off. So may take a lot of experimentation to get the set voltage for the VSR just right. Ultimately forget the whole idea and just charge your lithium pack when you need to. ol'will
longjohnsilver
Well-Known Member
How do you heat the water? Is it via an inverter which then powers your calorifier, or some other method?
KompetentKrew
Well-Known Member
I can't tell you how much I like this idea.
I have a decent pair of AGMs at the moment, together rated 330AH - I could use more capacity, but I am reluctant to replace them because they're in good condition; lithium would be so expensive and require messing with so much of the electrical system.
Diverting the solar to a single small lithium which would then charge the main bank makes a lot of sense - if sized correctly it would mean I get the maximum benefit from my solar throughout the day, even during the AGM's absorption and float stages.
How did you arrive at the capacity of 15% for your example, please @Kelpie? Just a wild estimate or for some specific reason?
Somewhat related question: how fully charged are the AGMs when the bulk stage completes? I can find figures suggesting 70%, 80% and 90%, but only the last one specifies AGMs, and I'm not sure if they're different from other lead-acid batteries in this respect?
geem
Well-Known Member
I kept it reasonably simple. Our 220v immersion heater is rated at 1200w. By applying 110v to the immersion heater the load then becomes only 300w. I have a cheap 110v inverter that supplies the immersion heater via a changeover switch and 1 hour timer. Once my batteries go to float I simply turn the timer on for an hour at a time. With 720w of solar and only a 300w draw from the immersion heater the batteries will stay on float if the sun is shining. It works well but generally needs a couple of hours to get enough heating for a couple of showers when on a hot climate
RupertW
Well-Known Member
My planned solution is similar except I’m using my normal 220v invertor but with a transformer to 110v. My possible overcomplicstions include a couple of vsrs and a switch between mains supply and invertor supply.
Kelpie
Well-Known Member
It's a very very rough guestimate, based on the idea that you can get to 90% SOC in your main bank before resorting to B2B charging from the LiFe battery.
I figured that that rounding up to 15% would give enough margin to cover the charging losses and to prevent complete depletion.
If you need to switch to B2B after only 80%, then the LiFe battery would have to be perhaps 30% of the main bank size. For a 400Ah main bank that means 120Ah LiFe, which is still easily within the realms of a single 'drop in' battery, although obviously starts to look expensive.
Pinning down these numbers accurately would be really interesting. Controlling the charging regime could also be tricky- maybe it could be done using a dual-bank charge controller, where priority is given to the LiFe bank?
geem
Well-Known Member
My 110v inverter was £30. Changeover switch was £20 and timer similar.
Pete7
Well-Known Member
That price is remarkably good, assuming they have Lithium inside them and you want to order the minimum of 50.
Do they need a blanket in the winter? you wouldn't want them getting cold whilst charging and pure Lithium transferring across the plates rather than the LI alloy, which can't be reversed.
What do you use on your Sadler?
KompetentKrew
Well-Known Member
Look again! There's a price break at 50, but also a price quoted if you're ordering fewer (even a single one).
Poey50
Well-Known Member
If you check again you will see that the minimum of 50 is for those who want some customised logo or packaging. There is no minimum order that I can see.
No, as you say, you really don't want to be charging them in temperatures under 5 degrees C (unless perhaps very slowly). Winston claim lower temperature charging for their prismatic LiFeYPo4 cells but have been reluctant to publish any research on this. For boats left in the water over winter, this won't be a problem but I will want to sometimes be able to charge with the boat on the hard in the cold so my pack of four cells will rest on a base which has a thermostatically controlled heating pad in it for those few occasions when I need to charge at low ambient temperatures.
For my Sadler I'm waiting on 271 ah of LFP which will be in four cells to make a nominal 12 volt pack. I have all the life-support ready for them. My whole set up has cost approx £1500 (including new charging) and will give me the equivalent usable capacity of 5 x 100 ah lead acid and occupy less space than one of these. If I don't mess them up the pack should see me through the rest of my sailing years which, with luck, is about 15.
As to whether they have any lithium in them, prices are proportionately in line with other sizes of these aluminium cased LFP cells. I'm aware, through specialist forums, of dozens of sales which have all been fine. Anyone interested in importing direct from China should join Will Prowse's DIY Solar forum. Look for posts by Ghostwriter especially, she has been importing for her company for years and knows more about it than anyone I've yet come across.
Last edited:
KompetentKrew
Well-Known Member
Yes, that was the reasoning I used too - it seems intuitive. I think this is the complement of the bulk-charge percentage - can I call it the "bulk complement"?
On reflection, I think it's just arbitrary though - I guess it's right if your solar panels are the exact right size to match your usage, and the only shortfall is because of the lead-acid's slow absorption stage. If perfectly matched the LiFe will be fully charged when the sun goes down and it will contain just enough to complete charging the lead-acid batteries overnight, and be empty in the morning.
But if you use more power than your solar panels produce then your AGMs will still continuously discharge, over a few days at anchor.
If, on the other hand, if you have a couple of days with less usage, or one or both of your batteries are full because you've just left shore power or run the engine, then some solar gathered during the LA's absorption phase that afternoon / evening will be wasted.
I think most of us are going to be confronting this because we don't have quite enough solar charging to keep up with our usage (any more panels would be unsightly!), so I think the real answer is to add as large a LiFe as makes financial sense to you - whether it's smaller or larger than the bulk complement, it's still reducing the amount your AGMs are discharged each day. If it's smaller it acts as a mitigator of waste, if it's larger it acts as an extension to your main AGM bank.
I hope this makes sense - I'm rather tired and may have lost the plot.
Your previous comment, that felt so right to me, followed shortly after Pete7 declared the first rule of boat maintenance to be "keep it simple, stupid".
I think the thing to do is have the solar panels charge straight into the LiFe battery (I'll need to learn what kind of charge controller is needed) and then have the LiFe battery connected only to a B2B charger, which is then connected only to the AGMs.
As I understand it, LiFe batteries have a safety cut off which prevents them being discharged below about 2%. But, aside from that, any charge you put into them, you can use immediately. So the LiFe battery will start charging the AGMs as soon as the sun comes up in the morning, and both batteries will charge from solar until they're full - the AGMs will fill first; once they have reached absorption stage the level of the LiFe will rise. If the LiFe is big enough then the AGMs will stay at 100% for some days.
The configuration I propose does not see the LiFe battery charged off the engine, if you run it, nor off shore power. But it is wonderfully simple, and doesn't require much messing with the existing charging equipment (alternator, shore-power charger); all the solar will go into the LiFe battery whilst the AGMs are being charged by those other sources, so it's probably good enough.
MarkCX
Well-Known Member
This exactly. The only thing added to a ‘simple’ system is a smallish LiFe battery with a B2B charger between the solar and AGM; it may no longer be simple, but nor is it particularly complicated. My charge controller wil happily charge a LiFe battery.
