Bargain lithium battery.

[MERL]

Whilst down Hereford in a few weeks time I'll be collecting 32 of these bad boys from Ross on Wye for my proposed DIY solar storage system.

Pardon our interruption...

ebay.us

They'll be making a 628Ah 48V 16KWh battery but built in 12v mode they would make one helluva 2500Ah leisure battery

 

[MERL]

Merl what do you think of the specs on those Ecoworthy batteries I got. I thought they looked alright with some nice features but I picked the wife because of looks but never looked at the spec look where that got me.

ECO-WORTHY 12V 314AH Lifepo4 Lithium Battery Bluetooth with SOC LEDs and Low Temp Protection | Eco Worthy

Upgrade your power solutions with Eco-Worthy's 12V 314Ah LiFePO4 Lithium Iron Phosphate Battery Bluetooth with SOC LEDs and Low Temp Protection when the data-collector be connected, so you can remote monitoring and control you battery through the ECO-WORTHY Smart APP, ensuring real-time access...

uk.eco-worthy.com

You shouldn't have any issues with those Wully

 

[Robmac]

Whilst down Hereford in a few weeks time I'll be collecting 32 of these bad boys from Ross on Wye for my proposed DIY solar storage system.

Pardon our interruption...

ebay.us

They'll be making a 628Ah 48V 16KWh battery but built in 12v mode they would make one helluva 2500Ah leisure battery

How many BMS would you need for those Merl?

 

[MERL]

How many BMS would you need for those Merl?

Just 1 Rob.
The 32 cells get paired up in parallel so effectively you now have 16 cells at 628Ah. You then connect those 16 cells in series to make a 48V battery pack.
You control that pack with a single BMS compatible with 16cells (called 16s). Because the voltage is a lot higher than our leisure systems the current is comparatively low and a 200A 16s BMS is a similar price to a 200A 12V BMS and good for nearly 10Kw. On a 12v (4s) system you only get a quarter of that!

 

[Robmac]

Just 1 Rob.
The 32 cells get paired up in parallel so effectively you now have 16 cells at 628Ah. You then connect those 16 cells in series to make a 48V battery pack.
You control that pack with a single BMS compatible with 16cells (called 16s). Because the voltage is a lot higher than our leisure systems the current is comparatively low and a 200A 16s BMS is a similar price to a 200A 12V BMS and good for nearly 10Kw. On a 12v (4s) system you only get a quarter of that!

Have you decided on Solar Panels yet Merl.

That would be a great system for a completely off grid narrowboat which have the roof size for lots of solar!

 

[Geek]

Thing is, Lithium is only around half the resistance of lead acid therefore a 100Ah lithium is approximately the same internal resistance as 200Ah of lead acid. People have been doubling up there lead acid for years without a second thought for this action 'burning out their alternator ' .
Fact is the vast majority of motorhomes have sufficient cable length between alternator and leisure battery that the halving of the battery resistance pales into insignificance compared to the cable resistance.
Lithium's voltage over the bulk of its charge cycle is higher than lead acid, therefore the voltage differential is less and therefore the current is lower than lead acid.
I'm planning a revamp of my system and my B2B is coming out and I'm charging directly with the alternator, with the correct cable length and guage the current can be controlled to give me what I want.

I look forward to hearing how well that went. It would be great if it worked.
The lower internal resistance isn't the defining difference with lithium batteries. What makes the big difference is the voltage response to charging current.
A lead acid battery's voltage rises a fair bit as it charges, whereas a lithium battery sits at more or less the same voltage despite charge current. This is inherit in the chemistry, not just a matter of internal resistance.
The alternator sits there at the bulk charging stage for hours on end with the current not dropping and the voltage not rising.
I see this happen on the side-by-side meters on my dash: one shows the current and voltage of the lead acid bank, the other of the lithium.
It would be great if your idea works well in the long term, but I fear for your alternator's health.

 

[Geek]

Lithium's voltage over the bulk of its charge cycle is higher than lead acid, therefore the voltage differential is less and therefore the current is lower than lead acid.

That is the opposite of my experience.

 

[MERL]

A lead acid battery's voltage rises a fair bit as it charges, whereas a lithium battery sits at more or less the same voltage despite charge current. This is inherit in the chemistry, not just a matter of internal resistance.

As we've previously touched on in a different thread, what you're referring to is the additional voltage needed to drive the actual chemical process of charging, this is called overpotential.

True, the overpotential isn't as high with LFP as lead acid BUT the base voltage to which the overpotential is added is generally higher with LFP...the upshot is that for a given current and similar SOC the battery terminal voltage of LFP is nearly always higher than lead acid and therefore the charge current is lower. The exception is when the LFP is at a very low SOC and the potentially high current needs to be protected against.
I'll have to have some sort of split charge relay, I may do that with a large Relay a-la Trev BUT I may go for a Durite VSR (I may not though because I've had experience of them behaving oddly!) Anyways.. whatever I use I'll be able to turn charging off either manually or automatically with a current sensor if need be but ultimately I'll be able to control the maximum current with sufficient resistance in the charge circuit. My gut feeling is there'll be a 'magic distance' between alternator and LFP battery, once that distance is established then all you need to do is choose a cable gauge and that gives you the correct charge current. Eg, at the magic distance 2.5mm cable will give you 12A max current which is permissible for 2.5mm cable( 5X cable gauge in mm = max current rule of thumb), if you double up the cable gauge you double up the charge current, triple the gauge you triple the current and so forth BUT the current will never exceed the cable capacity providing you don't go shorter than the magic distance so all you need to know is the magic distance and then you choose a max charge current and divide by five for the cable gauge. Simple eh!
That's the theory and as you say it'll be interesting to see how things go but my colours have been nailed to the mast on here so I WONT be able to experiment first, post my findings and then make out I knew what would happen after the event! . I'm considering filming it and sticking my findings on youtube??

 

[Geek]

Calira system which states a max battery capacity of 200 amps

When a battery charger specifies a maximum battery size, you can't really tell why.
Perhaps the long-term cooling of the charger is suspect and it might overheat if running at full pelt for a while.
Perhaps it is well enough cooled to maintain a steady temperature, but the end of the bulk charge phase is set by time rather than current profile.
Perhaps the charge phases are set by detected current and a big battery never comes out of bulk.
Perhaps they set an arbitrary battery size limit so you will pay more for a larger model in the range.
They never tell you the reason for the limit.

 

[Geek]

As we've previously touched on in a different thread, what you're referring to is the additional voltage needed to drive the actual chemical process of charging, this is called overpotential.
View attachment 150764

True, the overpotential isn't as high with LFP as lead acid BUT the base voltage to which the overpotential is added is generally higher with LFP...the upshot is that for a given current and similar SOC the battery terminal voltage of LFP is nearly always higher than lead acid and therefore the charge current is lower.

As I said, my experience is the opposite of that. I have two battery banks in parallel, charged by the same b2b charger, monitored by hall effect sensors (so no voltage loss) and the lithium consistently charges at a lower terminal voltage and a higher current.

The exception is when the LFP is at a very low SOC and the potentially high current needs to be protected against.

This doesn't apply for me: either bank could happily take the full output of the b2b.

I'll have to have some sort of split charge relay, I may do that with a large Relay a-la Trev BUT I may go for a Durite VSR (I may not though because I've had experience of them behaving oddly!)

The only reason I can see to use a VSR is to avoid having to connect a lead to d1.

Eg, at the magic distance 2.5mm cable will give you 12A max current which is permissible for 2.5mm cable( 5X cable gauge in mm = max current rule of thumb), if you double up the cable gauge you double up the charge current, triple the gauge you triple the current and so forth BUT the current will never exceed the cable capacity providing you don't go shorter than the magic distance

I'm not really sure I follow what you mean by cable gauge of 2.5mm. Gauges are generally integers, and get smaller as the cables get bigger. Double the gauge and the wire is thinner. To me, this is nearly as daft as using 'cups' in recipes. I suspect this isn't what you mean.
My batteries are connected using 25mm2 cable or more (mostly). Are you talking about wires with a cross section of 2.5mm? A diameter of 2.5mm?
A radius of 2.5mm? That might be reasonably chunky.

 

[MERL]

That is the opposite of my experience.

Thanks, I admit i've yet to test but that's not what published data says but admittedly that data will be for brand new LA batteries, LA soon goes 'soft' with cycling and age and consequentially the terminal voltage rises and charge current drops off. How are you doing the measuring/testing and what's the age of the LA? What's the capacity of the LA compared to the LFP? What's the SOC of the LA compared to the LFP? I know you've got a hybrid system...I'd have expected the LFP to do the donkey work for the first 3/4 of the discharge cycle and then the LA to catch up and finally take over, if so then the LFP will typically draw more charge current in a parallel setup because it's higher potential means it get's discharged sooner than the LA.
Ultimately 200Ah of brand new lead acid would have an internal resistance similar to a 100Ah LFP battery and 200Ah of new lead acid would have been installed a gazillion times in the past in a gazillion motorhomes without a second thought about the low internal resistance burning out their alternator.

 

[MERL]

the lithium consistently charges at a lower terminal voltage

Surely the terminal voltages are pretty much identical....after all they are connected in parallel. The only difference in terminal voltage is cable volts drop under load, that should be tiny unless you've used under sized cables? Im guessing the difference is a few millivolts and down to whats mentioned in the thread above.

I'm not really sure I follow what you mean by cable gauge of 2.5mm. Gauges are generally integers, and get smaller as the cables get bigger. Double the gauge and the wire is thinner. To me, this is nearly as daft as using 'cups' in recipes. I suspect this isn't what you mean.
My batteries are connected using 25mm2 cable or more (mostly). Are you talking about wires with a cross section of 2.5mm? A diameter of 2.5mm?
A radius of 2.5mm? That might be reasonably chunky.

Not getting into pedance Geek and I'd appreciate it we can keep this a sensible technical discussion so come on mate....you know exactly what 2.5mm cable is....dont be a dick, you're better than that.

 

[marchie]

Surely the terminal voltages are pretty much identical....after all they are connected in parallel. The only difference in terminal voltage is cable volts drop under load, that should be tiny unless you've used under sized cables? Im guessing the difference is a few millivolts and down to whats mentioned in the thread above.

Not getting into pedance Geek and I'd appreciate it we can keep this a sensible technical discussion so come on mate....you know exactly what 2.5mm cable is....dont be a dick, you're better than that.

My [very] limited electrical knowledge suggests that, if it's cable we're talking about, it's more likely to be impedance we should be discussing ... but not for use in the ohm ...

Steve

 

[MERL]

My [very] limited electrical knowledge suggests that, if it's cable we're talking about, it's more likely to be impedance we should be discussing ... but not for use in the ohm ...

Steve

Resistance for DC, Impedance for AC Steve

 

[Robmac]

Resistance for DC, Impedance for AC Steve

I think he was being impedantic Merl.

 

[MERL]

I think he was being impedantic Merl.

Now that was either brilliant or I'm dumb and slow and missed Steve's joke( which I admit I do with most of Steve's puns.)
Claim it Rob before Steve does.

 

[marchie]

Resistance for DC, Impedance for AC Steve

Told you that electrical knowledge is limited, Merl - bright as a glow worm's armpit when it comes to this topic ... . But I do understand syntax, which is more than the BBC sports journalists do - they report that Garnacho was fined for 'speeding to Liverpool Crown Court' which would require 2 prosecutions - one for speeding when leaving the Man Utd Training Ground, and a second for speeding to Liverpool Crown Court ...

Steve

 

[Nabsim]

When a battery charger specifies a maximum battery size, you can't really tell why.
Perhaps the long-term cooling of the charger is suspect and it might overheat if running at full pelt for a while.
Perhaps it is well enough cooled to maintain a steady temperature, but the end of the bulk charge phase is set by time rather than current profile.
Perhaps the charge phases are set by detected current and a big battery never comes out of bulk.
Perhaps they set an arbitrary battery size limit so you will pay more for a larger model in the range.
They never tell you the reason for the limit.

My understanding, (which could be wrong) was you could safely use 10x the a/ah output of the charger without any risk of overload. These days decent branded chargers probably don't have any such restriction but I remember checking with A and N caravan services (very respected for this in the days before lithium) and that's what I was told. Last time I checked the web site was still up with all their findings, I think it may be you can go to 15x the output but not double checked so stayed safe at 10x. Of course that applied to LA technologies not to lifepo4 that will take much more current.

It was due to the charger build, big differences between makers back then from what you can read on the net. I know for a fact it doesn't apply with Victron chargers, I can connect either one or both my 30A chargers to my 2 x 100 lifepo4 and even when I have run them to 0 SoC they cope fine (mine are ca[able of charging at 50A each).

All above except what I have done myself is advice off the net, you and Merl lost me on technicalities many posts back lol

 

[MERL]

Told you that electrical knowledge is limited, Merl - bright as a glow worm's armpit when it comes to this topic ... . But I do understand syntax, which is more than the BBC sports journalists do - they report that Garnacho was fined for 'speeding to Liverpool Crown Court' which would require 2 prosecutions - one for speeding when leaving the Man Utd Training Ground, and a second for speeding to Liverpool Crown Court ...

Steve

Each to their own Steve, everyone needs a hobby eh
I remember a coffee spurt moment when the BBC news common tater was announcing the retirement of Nicola Adams the British boxer, she said Nicola had decided to retire because " She was tired of being punched in the ring".
Surely that's not legal under the Marquis of Queensbury rules?

 

[marchie]

Resistance for DC, Impedance for AC Steve

Told you that electrical knowledge is limited, Merl - bright as a glow worm's armpit when it comes to this topic ... . But I do understand syntax, which is more than the BBC sports journalists do - they report that Garnacho was fined for 'speeding to Liverpool Crown Court' which would require 2 prosecutions - one for speeding when leaving the Man Utd Training Ground, and a second for speeding to Liverpool Crown Court ...

Steve

Each to their own Steve, everyone needs a hobby eh
I remember a coffee spurt moment when the BBC news common tater was announcing the retirement of Nicola Adams the British boxer, she said Nicola had decided to retire because " She was tired of being punched in the ring".
Surely that's not legal under the Marquis of Queensbury rules?

Akin to Jeremy Thorpe's Memoir about his career as an amateur boxer - 'My Hammerings in the Ring'

Steve