Which leisure battery ... not what oil

So, you're saying you will operate it manually and "keep your eye on it". I think that's fine for an addicted tech head such as yourself but for most people it's a golden opportunity to dispose of income in a flash of "one mistake and it's knackered". We're a long way from fit and forget for dummies aren't we? lol

But that's exactly what I'll be wanting for the boat - if I can't have that along with a lot of capacity I'll be staying in the marina plugged into 240 mains. My worry would be that my power usage will require me to run the engine for 4 hours every day even with lithiums. I'm ignoring the summer solar situation and planning for the worst winter engine running scenario.

But I'm just reading up at the mo, I haven't even worked out how much power my little studio gobbles up but I seem to remember fitting a 750w PSU in the PC and have 2 x powered monitors (speakers) and a 25" screen. Sod the fridge! I must get one of those plug in the socket power monitors from ebay and see what I'm up against but it ain't going to be encouraging. I think I may have to convert my domestic alt with a programmable regulator AND use the travelpower at the same time. My engine is going to hate me, just as well it's a good 'un without too many hours on it!

 

Yup. The lithium's scare the BJ out of me if I'm honest. It's a lot of money to waste if it goes wrong and like you we are planning the syncro for absolute worse case scenario.
That's why these situations become so complicated. 90 percent of the time it's no Biggie if something fails.
But, we have been up at altitude in the Pyrenees with a failed battery, no heat, no lighting and miserable. And I have nearly thrown us down a sheer cliff in the Atlas mts when the weather turned on us and the road turned to a river of mud coz the tyres that got us there couldn't cope!
We want to do more of that, and unfortunately one of the costs is having to be more aware of the systems and trying to get the best balance in terms of performance and reliability.

 

Well although I'm glad I started it, because I gleaned what I needed, I'm also sorry I started it!
My brain can only cope with a "Which?" style comparison grid I'm afraid .... Becomes like listening to the weather forecast with the best of intentions and waking up half an after it's finished with barely a scrap of info securely stored
FWIW, as we have a pre-smart alternator (2009 van) we went for the most recent incarnation of a flooded battery ... "EFB" ... a Yuasa L36-EFB as opposed to the standard L36-100.
Halfords kindly had a voucher code on, so £99.
I'll be coming back to this thread when an mppt finds its way onto the wish list, for solar

 

No need , just buy an Epever like everyone else - they work ...


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Which solar panel? They don’t all work.

 

Don't start!
I'm not going to think about it for a while ... Only just got the 240/12v leisure electrics organised.
Since you ask though, "CIGS" appeal

 

Still plenty of choice there, but

 

The problem with all battery chemistries is that they are all based on one chemical reaction that stores energy and then other reactions that either waste energy by making heat and gas or recover some energy ( the gas pressure in a sealed lead acid forcing the hydrogen and oxygen to recombine releasing heat.). Plus straightforward resistive heating.

The voltage across the terminals is a combination of the "real" battery and these other effects.

As soon as you try to both charge a battery and draw power from it your charger's model of the battery is wrong. The real voltage across the battery is then somewhere between "charging voltage no load" and "discharging voltage full load", and you dont know.

Basically the only route to 100% charge is a system where the charger source connects to the battery and charges it, while the load current is independently drawn from the charging source, and the load is only connected when the charging source is disconnected.


Like in @Zed s case, all his kit in the boat is run off the engine mounted mains generator while the engine runs, charging the batteries off the alternator in a single charging cycle .
With solar you again need to take the load from "before" the battery charger but be able to automatically quickly switch to "best effort" with the load coming from the battery if it exceeds what the solar panels can produce.

Unless your lead acid battery management system is fully integrated with boxes that inform each other of their "beliefs" you might as well stick to cheaper solutions.. otherwise the smartness of a B2B will completely "mind flay" the smartness of a smart charger trying to charge the source battery in a B2B system.
Basically you can spend a lot of money for some charging advantage and a lot of time with customer support.


There is also the "I spent a load of money so it must be good" syndrome..

Otherwise, just having the fridge cycling will keep dropping the battery voltage and causing the charge cycle of a battery charger to restart.. the fridge load makes the battery seem less charged than it really is. And that may either make the charger overcharge or undercharge the battery dependent on its particular algorithm..
One algorithm may keep hammering away and never stopping producing gas and heat, another recognises the load and abandons ever trying to complete the full cycle.

For most of us, a simple solution with a Ctek/Victron charger, an Epever/Victron MPPT if solar on a wet cell leisure battery and a VSR will do. K.I.S.S.

 

Actually I have many choices, at the mo I'd just let the domestic alternator (120A) charge the batteries and only use the travelpower for tools. The idea of using the inverter/charger and travelpower was for lithium fast charging which avoids having to buy a flashy alternator controller to stop the domestic 12v one overheating. Cooking alternators while charging lithium batteries is so common it's a given. I have 3 alternators on my engine, 1 for starter batt, 1 for domestic back, 1 for the travelpower.

 

A changeover relay could be added to isolate the leisure battery from the load when the engine is running allowing a B2B to charge it while the alternator/starter battery supplies the leisure load. Engine off the relay would isolate the starter battery and redirect the load to the leisure battery. Would that work?

 

Could I try to boil that down a bit?
Would any set up that avoids discharging and charging a battery at the same time be the way to go?

 

I wouldn't worry about it.
In the real world we travel with the fridge switched on and charging other appliances, the batteries are being charged with the alternator and vsr.
When static, the panels charge the batteries whilst appliances are working.
When hooked up, the ctek charges happily whilst we are using appliances.
It's been this way since I installed our system in 2014.
Properly fit and forget...
We don't kill batteries, in fact they last well considering the use they get. The starter is the original one we bought back then, the lb has just been changed but only because the old one has been pressed into use as the boat starter!

 

@Dub and Dubber , just to 'perspectivise' that Mike our trips are usually plus 3 months in duration outside of the pandemic restrictions but we did live in the bus last Autumn 2021 for about 7 weeks whilst the boat was being overplated.
No hook-up, just in a field with solar to keep everything ticking over. I turned the fridge off at night, but we were using the propex and lighting in the evening as it got cooler.
Like all this stuff we all have, it works better and more reliably the more often it gets used

 

As I put it my conclusion is: for average bus users, don't overthink or over do it.

Adding complexity or manual switches can create problems as fast as you solve them.

To thoroughly kill an AGM : run it flat, disconnect it from the charger by leaving the switch off and leave it for a week.

To thoroughly kill a Wet lead acid, run it flat, and leave it a bit longer.

A lithium battery's BMS will protect it from the idiot, because without a BMS it would be a danger.

 

Yes that would help ensuring you have 100% at the end of a drive.