Turbo-charging Motorhome Electrics

[mb2tv]

Very interesting!
Very good idea, though not applicable to me (i worry about weight, maybe too much).
He is not saying, but what about charging in cold temperatures? Is it enough to trust the BMS to stop the LiFePo4 from charging or extra protection needed?
Other than that, I cannot fault the idea, best of both worlds.

 

[wildebus]

Very interesting!
Very good idea, though not applicable to me (i worry about weight, maybe too much).
He is not saying, but what about charging in cold temperatures? Is it enough to trust the BMS to stop the LiFePo4 from charging or extra protection needed?
Other than that, I cannot fault the idea, best of both worlds.

In the case of the video, Clark (and Emily) spend their time in the tropics and their main trouble is keeping cool enough
In my case, this is why I wanted the Subzero model with its integral heater - this will charge normally at ambient temperatures down to -20C (I don't really intend to be going places that cold - and the battery will also be inside (under the seat) so even if it is really really cold, inside the motorhome won't be that cold anyway )

 

[xsilvergs]

I work on the theory that battery heaters aren't required as if they freeze I'll be frozen to death anyway

 

[wildebus]

I work on the theory that battery heaters aren't required as if they freeze I'll be frozen to death anyway

For internally fitted batteries, that is a fair assessment when unattended overnight it is something to consider though (but lithiums can be left without charge for many months of course)

 

[wildebus]

Did a load test on the battery over the last 24 hours, and also pulled some data from the 300Ah Lead Carbon (PbC) AGM Battery Bank.
With this info, I've mapped AmpereHours out the batteries and how the Battery Voltage drops as the energy is removed. On the basis that the two battery types will tend to equalise each others voltage levels (an electrical version of a communicating vessel), you can look at a voltage and have a good idea of how many AHs have come out of the LiFePO4 Battery and how many out of the PbC AGM Bank out of the total drawn AHs.
Once the two banks are combined, will be able to check against this theory

Voltage scales are the same. The X Axis' are AHs drawn so vary between the two graphs.

A few data points ....

At 13V, would have drawn 49 AHs from LiFePO4 and NO AHs from PbC AGM - 49 AHs in Total
At 12.75V, would have drawn 86 AHs from LiFePO4 and 40 AHs from PbC AGM - 126 AHs in Total
At 12.5 V, would have drawn 95 AHs from LiFePO4 and 95 AHs from PbC AGM - 180 AHs in Total
At 12.25V, would have drawn 98 AHs from LiFePO4 and 147 AHs from PbC AGM - 245 AHs in Total
At 12.0 V, would have drawn 99 AHs from LiFePO4 and 193 AHs from PbC AGM - 292 AHs in Total

You can see that the initial demand will come from LiFePO4 exclusively until around 80AHs are drawn and after that point the PbC AGM essentially takes over. This is what the maths says .... Let's see how it matches up

 

[mb2tv]

Can i ask a related (and a bit not related) question?
Why did you choose the specific battery? Beside the fact that it will work to -20°C, why the specific make?
I tried to look at batteries a bit, and there is quite a lot of choice, and quite a wide range of prices, so interested in how you chose this one.
Many Thanks

 

[wildebus]

Can i ask a related (and a bit not related) question?
Why did you choose the specific battery? Beside the fact that it will work to -20°C, why the specific make?
I tried to look at batteries a bit, and there is quite a lot of choice, and quite a wide range of prices, so interested in how you chose this one.
Many Thanks

Well .... This would have been my choice of battery as it has the heater and bluetooth features for what is a very good price point (IMO).
I have also found the manufacturer (Poweroad) very responsive in terms of technical support and feed back on the features and they respond back to emails within 24 hours which is something I appreciate.
So I would get this battery anyway for these reasons - would maybe have had to wait a while to do this setup but was able to arrange to get this unit from Poweroad to have a play with, so I'll be feeding back anything which I think might be useful to them (but doesn't change what I am planning to set up).
An alternative option for cheap Lithium solutions is to go down the DIY route with Lithium which can be an attractive proposition and in the past may have done that but for some reason just couldn't get enough enthusiasm to do that.

 

[Markd]

Who's watching Line of Duty?

"This convinced me that I should definately give it a go so I got hold of a Subzero battery . . '

Now we know who H ireally s

 

[wildebus]

Who's watching Line of Duty?

"This convinced me that I should definately give it a go so I got hold of a Subzero battery . . '

Now we know who H ireally s

Jesus, Joseph, Mary and the wee Battery.
Fitting lithium and now we're sucking current.

 

[Nabsim]

Can i ask a related (and a bit not related) question?
Why did you choose the specific battery? Beside the fact that it will work to -20°C, why the specific make?
I tried to look at batteries a bit, and there is quite a lot of choice, and quite a wide range of prices, so interested in how you chose this one.
Many Thanks

I haven’t checked but from memory () my batteries work down to -20 and they are just plain Lifepo4. It’s the charging side that changes with temperature

 

[wildebus]

100Ah LiFePO4 Battery fully recharged overnight following the discharge test and now installed this morning in the Motorhome alongside the 3 100AH Lead Carbons.
Installed a BMV-700 Battery Monitor on the battery so I can see and log all the current in and out. This is wired up as a "sub-monitor" to the main BMV-712 so the 712 tells me the overall picture and the 700 tells me what part the Lithium Battery is playing (which means BMV-712 minus BMV-700 tells me what is happening with the Lead Carbons).

The Voltages will always be identical as the batteries are in parallel, but the current is the interesting bit of course The graph capture below is while the EHU is plugged in so the batteries are idling while the charger is in float mode.

As added extra monitoring for the new battery, decided to also move the cabling for the original habitation electrics from the midi fuse block to the MPPT 100/20 Load Output. This means it is limited to 20A maximum output, but shouldn't be a problem as the hab electrics are fused at 20A as standard anyway. The reason I wanted to move it is for better granularity in the info.... With the Hab electrics on the Load Output, I can see precisely how much power is being drawn at any time which can be handy when you have a charger that Victron does not log data for (e.g. the Ablemail B2B in my setup).

Going to turn off the EHU later this afternoon which will have the Fridge running off the new LiFePO4/PbC Hybrid Battery Bank and look at the pair of Monitors and see if my maths are up to scratch
Want to delay the switch-off also so the Fridge will still be running on the inverter in the morning when hopefully it will be a nice sunny day and get some solar recharging

 

[PeteS]

Are you not concerned that the Lifepo4 might just top up the AGMs and basically take care of the self discharge you get? I havent watched the video yet but I cant get away from that observation.

 

[wildebus]

Are you not concerned that the Lifepo4 might just top up the AGMs and basically take care of the self discharge you get? I havent watched the video yet but I cant get away from that observation.

That is just what will happen, yes.
Clark, the guy who did the video, made this point and that it is important that your Lead batteries must be in reasonable condition so that the self-discharge is not too great.
My Lead Carbon Bank takes around 0.3A when on float. Not a problem.

 

[PeteS]

So slightly tongue in cheek you've just installed a really expensive float charger.

I can see the benefit if your living in the van regularly and you need high demands of current but if you hadnt already got the AGMs there would be no point in mixing the tech

 

[wildebus]

So slightly tongue in cheek you've just installed a really expensive float charger.

I can see the benefit if your living in the van regularly and you need high demands of current but if you hadnt already got the AGMs there would be no point in mixing the tech

I think it is worth while you watching the video to understand the concept and benefits better.

 

[PeteS]

Entertaining video, he has a good delivery style, if I was a patreon I would ask him and you maybe able to show it but I cant help but think that as the Lithium starts to drop below 13.2 ie towards the end of its capacity and you still have load requirements such that it contimues to drop that the Lead Acid is going to start to put large amounts of its capacity into charging the lithium, I dont see how you can stop that and I'm thinking it will be significant current although the more current the lithium wants the more the voltage will drop so maybe it wont be so bad.

For him to go 5 days without sun his bank of lead acid must be large, he doesnt really discuss what he has so I wonder how much he supplements with Lithium.

Interested to see some current graphs of flat lithium and fully charged AGMs even if they are at the same voltage.

I'm yet to be convinced but only because I dont know how the relationship between the Lithium and the lead acids will work with a fully discharged lithium.

 

[SquirrellCook]

Entertaining video, he has a good delivery style, if I was a patreon I would ask him and you maybe able to show it but I cant help but think that as the Lithium starts to drop below 13.2 ie towards the end of its capacity and you still have load requirements such that it contimues to drop that the Lead Acid is going to start to put large amounts of its capacity into charging the lithium, I dont see how you can stop that and I'm thinking it will be significant current although the more current the lithium wants the more the voltage will drop so maybe it wont be so bad.

For him to go 5 days without sun his bank of lead acid must be large, he doesnt really discuss what he has so I wonder how much he supplements with Lithium.

Interested to see some current graphs of flat lithium and fully charged AGMs even if they are at the same voltage.

I'm yet to be convinced but only because I dont know how the relationship between the Lithium and the lead acids will work with a fully discharged lithium.

I think it’s all based on voltage differentials e.g. a lower voltage battery will not charge a higher voltage one. I don’t know about lithium, but 12 volt lead acids require something like 2 volts above their current voltage to take a charge. I might be off with the numbers, but I’m sure the theory is sound.

 

[wildebus]

Entertaining video, he has a good delivery style, if I was a patreon I would ask him and you maybe able to show it but I cant help but think that as the Lithium starts to drop below 13.2 ie towards the end of its capacity and you still have load requirements such that it contimues to drop that the Lead Acid is going to start to put large amounts of its capacity into charging the lithium, I dont see how you can stop that and I'm thinking it will be significant current although the more current the lithium wants the more the voltage will drop so maybe it wont be so bad.

For him to go 5 days without sun his bank of lead acid must be large, he doesnt really discuss what he has so I wonder how much he supplements with Lithium.

Interested to see some current graphs of flat lithium and fully charged AGMs even if they are at the same voltage.

I'm yet to be convinced but only because I dont know how the relationship between the Lithium and the lead acids will work with a fully discharged lithium.

Hi Pete.
He does actually say how much Lead he has .... 1500Ah. Quite a bit there but simply the less you have, the less time you can go between charges of course.
It does take a few mental to's and fro's to really get your head round the idea but when I saw his video it really did crystallize the thoughts I had already along this line and convinced me it was a sound theory.

In terms of the Lead putting large amounts of its capacity in the lithium, it is very much as SquirrelCook says "I think it’s all based on voltage differentials e.g. a lower voltage battery will not charge a higher voltage one" as we would all agree I think, and why this concept works is that the 'natural' voltage of a Lead battery is so much lower than a Lithium battery - which is why the Lithium Battery will neither take a lot of energy out the LEAD, or fully discharge.

It is a little early to present this graph as it does not cover the full discharge-charge cycle, but I think it is interesting to see ...
This is the data from 17:00 yesterday until 10:00 this morning. All batteries started fully charged (there is some use in place already as I forgot to change a setting on the new BMV but it doesn't change the basic pattern shown).
Lead Data is red, Lithium Data is Green.
The Left Y Axis is in AHs and the Bars are AHs used (stacked to show the total for the whole bank) and are cumulative values as time elapses.
The Right Y Axis is in Amps and the Lines are Amps out/in for each Battery (-ve values is current drawn OUT of the battery)

OK, to explain as I read the data....
At the start of the time, you can see that pretty well only the LiFePO4 battery (green) is doing anything. The green bar keeps growing and PbC AGM bar (red) is pretty static.
This is the case for the first 9 hours or so and then - as the voltage of the Lithium battery drops as it gets to around 80% DoD (80Ah), the Lead batteries essentially take over. I guess the quiescent point when that happens is where the two current lines cross over?
From that point, the LiFePO4 battery starts to hover at around the 85% DoD mark - when there is a higher demand, it contributes a bit, and when the demand goes, it takes back some power from the Lead bank to get back to what would seem to be its 'settle' point

This next graph illustrates that - drilling down into a specific hour you can see what the current for each battery looks like

At the start of that hour, there is a power demand (the new Purple line is the current demanded from the battery bank as a whole) that is met from both the Lead AND Lithium batteries. But when that higher demand goes away around 27 minutes past the hour, the green-dotted line goes below the 0A line - in other words, it is taking power from the Lead bank - but only enough to make up for what it gave up the 30 minutes before to keep at around 85% DoD rather than to actually recharge.
I see this is a function of the voltage differences between the technologies and is the core reason why this kind of Hyrid setup can work.

Very shortly the overall SOC will hit 60% which means the intermittant high demand of the fridge will go as it disconnects from the AC, and the overall setup goes into one of Charging rather than Discharging - and so we will see how the solar harvesting gets distributed to the two different battery technologies ....

 

[PeteS]

Thank you very much for taking the time to post that, interesting, I get my head around it but I am surprised that the AGM are contributing early on, you seem to have a 10Ah drain which I would have thought the lithium would have coped with as well as float charging the AGMs unless the AGMs have a higher float charge requirement than FLA.
Maybe you need another 100Ah of Lithium to stop that happening.

Speaking of charging the AGMs how are you going to charge your setup as the AGM have to have 14.4V charge dont they to maintain performance and I suspect you dont want to take your lithium to that sort of voltage regularly??

 

[wildebus]

Thank you very much for taking the time to post that, interesting, I get my head around it but I am surprised that the AGM are contributing early on, you seem to have a 10Ah drain which I would have thought the lithium would have coped with as well as float charging the AGMs unless the AGMs have a higher float charge requirement than FLA.
Maybe you need another 100Ah of Lithium to stop that happening.

Speaking of charging the AGMs how are you going to charge your setup as the AGM have to have 14.4V charge dont they to maintain performance and I suspect you dont want to take your lithium to that sort of voltage regularly??

You need to ignore the initial 5Ah from Lithium and 5Ah from Lead - that was just a setup thing that I corrected but the data is still in the log for this time set. The key thing in the chart is the hour-to-hour change.
To confirm something here: the Ah numbers are cumulative - so if say the size of a bar has not increased from one data point to the next, then there was no additional value added. The bar size represents the total amount from the start, and not an addititional amount in each time period.
To show this in numbers, here are the first 4 data sets in tabular form:

Hour: 17	Total LiFePO4 AH Consumption: 5.0​	Total AGM AH Consumption: 6.0​
18	12.9​	6.4​
19	21.9​	6.8​
20	31.6​	7.3​

So between Hour 17 and 18, an additional 7.9Ah (12.9 - 5.0) was taken out the LiFePO4 Battery and 0.4Ah (6.4 - 6.0) out the AGM.


Ref the AGMs contributing early - something that is often quoted but is a fallacy is that there is no voltage drop under load with Lithium. It is totally true that it is not as apparent as it is with Lead, but it still happens. I would guess that the voltage sag in the bank is what is kicking in the AGM batteries to provide more contribution then maybe would be expected. But still talking under 1A from the AGMs bear in mind when the Lithium is giving 16A or more

Different Batteries have different charge levels. The generic "14.4V to charge Lead" is a commonly quoted thing but is another fallacy - There is a recommended range for every battery that the manufacturer provides. Also Lead Carbons typically tend to charge at a lower voltage and very similar to Lithium in fact. I used to charge at 14.2V (which as it happens is also the 'default' for LiFePO4), but I have reduced that slightly....
I have my Mains Charger set at 14.1V which is perfectly in range for the Lead Carbon AGM batteries as well as being totally good for the Lithium. I also have a slightly different Charge Voltage setting for the Solar - 14.15V. I like to have the Solar Controller settings slightly higher than the Mains so when the batteries are full and the chargers are in float, it is the "free power" from the Solar that does the maintenance.
Mains:

Solar:

I expected by now to see what the charging is going to look like after the fridge disconnected, but the SOC never actually hit 60%! it got down to 60.1% and then the system was getting just enough solar to stop it dropping further (typical when you don't actually want it!). It is 60.4% right now and overcast with rain, so can't see it staying over 60% for long.
Just rechecked .... system DID hit 60% SOC for one minute @12:09 and so the fridge disconnected. It is only 60.4% now nearly 2 hours later as the weather is so yucky.

I'll probably activate the mains charging in a couple of hours as solar will be doing nothing today
(UPDATE: going to turn the Mains Charger on now but limited it to 20A so around what you might expect on a decent sunny day so I can pretend it is solar .
Two things I want to watch for ... How the charge is distributed and if the BMV resets to 100 prematurely if the various parameters are met that it uses to define a 100% full battery - the distribution of the charge could after a time fool it in the same way they get fooled on intermittantly sunny days. We have 161Ah to put back into the battery bank at the moment!)