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Swapping to Lithium Battery
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userspirou
Posted: 19 January 2021 5:40 AM
Subject: RE: Swapping to Lithium Battery
 


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silverback - 2021-01-18 7:55 PM

very true, but you have all put me off now, don't want the van going up in flames
Jonathan

Don't see a point getting rid of them but an opportunity to check, possibly fix, how it was done. Unless you look at the entire system it's impossible to say whether it would work ok or not in each case and type of use. OK might not be perfect, but not unsafe. Presumably whoever installed it was happy with it?

For example, if you rarely use EHU, it won't really matter what type of mains charger you are using. A few cycles less is irrelevant. I would assume there is a B2B or something else controlling alternator output somewhere in the mix?

The problem on the charging side might just be that you're being sold 10000 cycles when in reality it will be half that because of how they are being charged. Not much different than with AGMs on the wrong charge profile where the promised lifetime is greatly reduced and you realise a much cheaper alternative would serve just as well.

And going the other way, no large loads also means you will not be overloading anything. In my van, if I turn on everything I possibly can, including inverter (small 250W), I will still be under 20 or 30A. No danger there...

My point is that you need to look at the entire picture and not just go and plug everything in because the battery itself can handle it and the brochure promised it can.
userDerek Uzzell
Posted: 19 January 2021 9:00 AM
Subject: RE: Swapping to Lithium Battery
 


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A couple of links that may be of interest

https://rvblog.co.uk/european-motorhome-tour/the-pros-and-cons-of-lithium-batteries-for-motorhomes/#comments

https://www.super-b.com/en/lithium-rv-batteries

For their 2021 collection Rapido offers (according to the model range) one 100Ah ‘maintenance free’ leisure battery with an optional 2nd, or one 92Ah AGM leisure battery with an optional 2nd, or one SUPER B 90Ah lithium battery with an optional 2nd. Where lithium batteries are a possibility, the motorhome model is stated as being pre-wired for lithium.

There’s a French Rapido price list here

https://www.autonews.fr/camping-car/actualite/camping-car-rapido-2021-les-prix-des-nouveaux-modeles-91512

but Rapido dealerships keep the cost of optional equipment close to their chests. Given that the retail asking-price of a 90Ah SUPER B lithium battery approaches 2000€, specifying a pair definitely would not be cheap.
userspirou
Posted: 19 January 2021 9:21 AM
Subject: RE: Swapping to Lithium Battery
 


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Did I put that bold sentence in there by mistake or someone edited for me?
userDerek Uzzell
Posted: 19 January 2021 9:46 AM
Subject: RE: Swapping to Lithium Battery
 


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Location: MODERATOR - 2015 Rapido 640F LHD 2.3ltr 150bhp


I did it.

It’s probable from Jonathan’s (silverback’s) earlier postings that no B2B was fitted to his Auto-Trail motorhome when the two lithium batteries were installed, but (as you’ve said) there MIGHT be something else controlling the vehicle’s alternator output.

As Johnathan is now considering rejecting the lithium batteries, it seemed important to me that his attention be drawn to your question - hence the bold.
userspirou
Posted: 19 January 2021 10:16 AM
Subject: RE: Swapping to Lithium Battery
 


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OK, no worries.

Seeing as though he saw only 16A flowing on that one outing there is most likely something restricting the current. But obviously can't tell what and how as I'm not familiar with his setup.
userarthur49
Posted: 19 January 2021 10:58 AM
Subject: RE: Swapping to Lithium Battery
 
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Much has already been said but we had an Autocruise PVC 6 or 7 years ago with Sargent EC155. When I looked at improving charging from alternator whilst driving, the big limiting factor was the EC155 and absolutely awful cabling to/from it. Little better than "bell wire". The EC155 has fusing of 20A to/from leisure and vehicle batteries so cabling will be a little better.

So I fitted a B2B and 25mm2 cabling to bypass the EC155 and existing cabling - B2B rated at 40A from memory. Worked a treat.

I wouldn't get rid of lithium batteries now I'd simply make sure the infrastructure round them could cope. I'm keen to fit lithium when my current lead-acids die but I will definitely not buy from any retailer who says they are a "drop in replacement"
usermikefitz
Posted: 19 January 2021 1:53 PM
Subject: RE: Swapping to Lithium Battery
 
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Spirou said,

' there is most likely something restricting the current.'

Its Ohms law.

The lithium battery has a very flat voltage characteristic of around 13v over 80% of its capacity range, rising steeply near full capacity and falling steeply near empty. If we assume the alternator is delivering 14.4 volts, and the lithium battery is half charged, the 1.4 volt difference and the circuit resistance limits the charge current. In simplistic terms, its the 'thin' cables and multiple connections between the alternator/engine battery and the lithium battery that's the control. As the lithium battery approached full capacity and the voltage rises, the current will fall to near zero. When the lithium battery is near discharged, the voltage difference will be higher and more current will flow in the circuit.

If you modify the circuit and use 'thick' cables and suitable interconnections, the characteristics of the alternator become more of a limiting factor. My tests show that the typical 150 to 200 amp alternator fitted to the Fiat and PSA range has a 'spare' capacity of around 75 to 95 amps at tick over and using short heavy duty cables will put these levels of current into my test, 220Ah, lithium battery.

However most information documents for converters issued by manufactures suggest around 50 amps is the maximum to be used for the 'caravan'. Fiat install a 'converters' connection point, rated and fused at 50 amps. Thus it would seem limiting the extra loading on the alternator within this value would be a more reliable option.

Replacing a lead acid battery in a typical motor home electrical system with a 'drop in' lithium battery without modifications to the system, whilst not ideal, should result in an acceptable system.
The weak point may be the mains charger having to work harder. Having all chargers with lithium settings and a more controlled charge from the alternator with suitable wiring and interconnection modifications would be ideal.

In many ways the lithium battery with its built in BMS is safer than a lead acid battery. It has built in current limits, responds in fractions of a second and shuts down with short circuits on the output or excessive currents, ( much faster than any fuse). It can not be over charged or over discharged.

Lithium batteries give outstanding performance compared to lead acid but need managing in a completely different way compared to lead acid for long service life. Unlike lead acid, lithium should be operated such that its below full capacity for most of its life. Thus any float voltage should be at a low voltage and leaving the battery on a continuous charge, is not recommended. I suspect in practice the cells will reach end of life due to natural ageing, rather than fail due to ill treatment or number of charge cycles.

If thinking about changing to lithium, research the specification carefully, particularly if using high power inverters. The maximum continuous current may be limited by the BMS to a low value. All the cells in a 100Ah battery will be rated to at least a 50 amps charge and 100 amps discharge. Depending on the quality of the BMS and the internal wiring inside the battery case, the continuous currents may be less.

Mike
userspirou
Posted: 19 January 2021 8:33 PM
Subject: RE: Swapping to Lithium Battery
 


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mikefitz - 2021-01-19 2:53 PM

Spirou said,

' there is most likely something restricting the current.'

Its Ohms law.

The lithium battery has a very flat voltage characteristic of around 13v over 80% of its capacity range, rising steeply near full capacity and falling steeply near empty. If we assume the alternator is delivering 14.4 volts, and the lithium battery is half charged, the 1.4 volt difference and the circuit resistance limits the charge current. In simplistic terms, its the 'thin' cables and multiple connections between the alternator/engine battery and the lithium battery that's the control. As the lithium battery approached full capacity and the voltage rises, the current will fall to near zero. When the lithium battery is near discharged, the voltage difference will be higher and more current will flow in the circuit.

I seem to remember heat is a byproduct of high resistance. And as such, I'm hoping thin cables and poor connections are not the sole, passive elements for current control in the system. Fine for momentary spikes such as in our first van which often still had batteries connected in parallel via 6mm2 wires when starting the engine. Can't say for sure as the battery monitor had a 1s resolution, but I do recall seeing 50A+ (but not 200+ actually needed) coming from the leisure batteries on such occasions. Sometimes they sell this as a feature (start assist), our case was just poor design and circumstance.

But, since electrical systems are not something I deal with every day, I'm always up for learning some new and useful tricks and will happily revise my views on the issue.
usersilverback
Posted: 19 January 2021 9:34 PM
Subject: RE: Swapping to Lithium Battery
 


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Hello all, and thanks for the replies, let me start by saying I don't want to hijack the original poster stevec176, but I am hoping he won't mind due to the fact of the interesting information.
next this is hard for me to digest because I have only limited electrical knowledge but to give a bit of an overview my system is the sargent EC 700 the charger is the PX300 the 2 x 102ah lithium are from ks energy with BMS the BMS has over charge overvoltage low temp cut off for charging all the usual stuff,
prior to me just dropping these in I asked Sargent and KS energy by phone if this was all possible, there reply was yes no problem it wont be ideal but it is okay to do so the charging regime by the solar and px300 was adequate and nothing will melt and the alternator will not desintigrate, the only niggle was that I did not have a B2B to charge them up more quickly (this part I will come to in a later post)
I invite you to read these links please then you might have an idea on why I came to my decision on the "drop in replacement battery"
https://sargentltd.co.uk/tech-support/article/Battery-Charger-Manuals/23
https://sargentltd.co.uk/tech-support/article/System-User-Manuals/22
https://www.ksenergy.co.uk/store/product/2-ks-lt100b-12v-100ah-bluetooth-high-power-lifepo4-lithium-leisure-battery
https://www.ksenergy.co.uk/lithium-leisure-battery-drop-in-replacement

I am sorry for the links but that is the only way for me to explain my decision
I don't use an inverter and if I have everything on it uses 25A
hopefully you can read the docs (have you owt else to do in lockdown? ha ha ) and give me your thoughts
Jonathan
ps thanks for the bold text it helped, but hopefully I can go onto B2B next.


Edited by silverback 2021-01-19 9:38 PM
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