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20 minutes of sweaty ranting? I'm not convinced...

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Having spent twenty minutes watching that I still disagree with a lot of it, I read an article a while ago that said most leisure batteries aren't proper deep cycling units just standard lead acid. I have also found some smart chargers will not charge a depleted battery if it doesn't get a voltage signal so you have to add another charged battery in parallel. I thought my alternator put out a charge regardless of what is connected to it and as stated in an earlier post the second battery will take whatever charge it required even if the main battery is fully charged. I might be completely wrong.

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Well I lasted 5 minutes into that... he says he considers himself an expert but, um, no.

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For the record my battery wasn't destroyed but it would have been if I'd continued with things as they were. I had a couple of long discussions with Enersys in Manchester and the feeling was that I had worked my Aux battery hard and not fully re-charged it after each discharge. I was fortunate that they recovered it, as I said, using a charge / discharge set-up that I wouldn't be able to replicate. The load test then showed that it followed a discharge curve that was still acceptable.

That's when I started looking and thinking about parallel battery charging and I eventually ditched the VSR and went for the "intelligent" dual charger from Ctek. I'm sure there were other things I could have spent my money on but I chose that.

In reading this thread and the comments, I still believe that two parallel batteries in differing states of discharge will not instantly cross charge and act as one. It's a chemical reaction that take time to reverse. I don't see a Starter battery pouring charge into an Aux at the rates implied. If one more highly charged battery (higher terminal volts) is sitting across the Alternator, then how can current flow into the other, which would have lower terminal volts if it were disconnected?

I watched the video just before writing this and I see where he's coming from. Thanks for posting it @dailysleaze.

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@Peaklander I drew a picture to help visualise how it works:

split_charge.png.3e6f9a48875039cc85da47491cab3ec9.png

The batteries are two buckets of electrons which are joined by the split charge. The alternator pours current in to the system, it just tries to maintain it's target voltage (level in the pipe) and doesn't know anything about the battery/batteries connected etc.

When the split charge joins the two you have two different levels, this is hopefully fairly obviously going to result in some charge flowing out of the starter battery into the leisure battery to try to equalise the level, while the alternator just sees the overall level change and pumps what it can into the system.

The starter battery can source a large current but a true leisure battery may not be able to receive it (hence the skinny pipe, representing internal resistance and the loss in the split-charge system), and as the voltage rises the flow will drop (less potential difference equals fewer amps into the load) which is why you'll rarely see much more than 10A flowing into a battery after the first couple of minutes (I even measured it once), so a 100A alternator is largely pointless unless you need 100A to run things while the car is on the move - which modern vehicles do (electric windows, seats, HVAC, PTC heaters, etc.) or if you're winching.

Also, because there's only so much charge (current) a battery can take it should make sense that there's only so fast you can pour water into the pipe before it overflows, even if the levels in the batteries aren't to the top.

As the voltage comes up, the current drops, this is why modern "smart" alternators and "smart" chargers can ramp the voltage up to 16 or 18v to push more charge in quickly - but obviously you need to KNOW the battery can take it (modern cars use a lot of AGM batteries designed for this) and that the thing doing the charging is suited to the battery type and not just trying to start a fire. :ph34r:

Because of this drop of current as the battery reaches full charge, voltage drop in wiring etc. it can take a long time to get that final 10% into the battery - on short journeys you may never get there. My measurements, minimal as they were, showed it took at least 30 mins for the charging current to drop off.

If you badly discharge your battery (beyond its rated capacity) you damage it and decrease its capacity and its ability to accept charge - like pinching the pipe on the "split charge". A smart charger can try to recover this by de-sulphation (sp?f?) to literally knock deposits off the battery plates with jolts of power, I've seen it work but it's never 100%.

 

We bought the odd battery from Enersys - and yes, if these went below their rated safe limit they would ALL be scrapped & replaced, no question;

IMG_0337s.JPG.9a25365276e00cbd7b3273bca2f166c5.JPG

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For bonus points in the Ambulance thread I've got data logs from our electronic load that shows the difference between a healthy battery and a dead/damaged one:

You can see that off-load the battery voltage sits fairly close to a healthy one, which is why I have a problem with devices like the National Luna which tries to equate battery voltage to capacity/health. The amount it drops under load tells the story though - its capacity has dropped massively and its internal resistance has gone up so it can't source or sink current anywhere near as well as a healthy one.

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Hi FF thanks for posting. I agree with all that. It’s the ability to complete the entire charge that is the issue and it where I still think that a vsr can’t do the job 100%  especially on old alternators  

That’s why I’m happy to use the Ctek unit as I know that the aux battery is now getting a complete charge. As I said, I was lucky to have not damaged it irreparably and now that I have the solar panel fitted the whole system is working well. In fact I have just refitted the panel today and watched happily as the volts ramped up ( both batteries are agm and the charger is configured for that).

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My issue with CTek, other than the price, is you have very little feedback that it's doing all the marvellous stuff they claim it's doing - you get a green LED or somesuch and just have to trust it's actually doing anything better than a £5 relay would've done.

Reading the D250SA / SmartPass manual it looks like it actually still just charges at 14.4v (or 14.7v for AGM) at a max of 20A, so I'm sticking with my relay.

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I have a panel mount voltmeter and can switch between the two batteries with a little toggle so I can at least see that bit but no current of course.

We have probably done this to death 😀 but what charging voltage do you achieve? Can you see 14.4v all the time?

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The alternator hits 14.4 happily, the solar chargers hit whatever they're set to.

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I hate to say this, but, wouldn't it be better to run a second alternator? That way no matter what drain you have on the leisure side of the electrics it will be totally isolated from the the rest of the car.... after all from what I can make out the idea is to not be forced to reach for the starting handle, if you're lucky enough to have one... or stuck in the middle of nowhere trying to bump start your rig:wacko:

Also correct me if I'm wrong, but wouldn't a twin alternator setup cost a lot less?

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Miggit - sorry but you've totally misunderstood the problem. When the engine is running the alternator is more than capable of charging two batteries. When the engine is off you separate them to avoid discharging the starter one by running fridges etc.

The discussion is over the gear used to manage the two batteries, plus things like solar panels.

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That, and the charging profiles for leisure and starter batteries are different, that's even before you have AGM, lithium or lead crystal batteries on board.

The Ctek boxes are proper battery management systems, not just a method of filling a bucket with water.

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Mr Freezer, isn't running two alternators the best way to totally separate the 2 batteries, as there would only be a common earth....

And Bowie69, I realise that there are different requirements from the battery types, but if you're using AGM for the leisure battery, surely it's easier to get 14.5 + volts from a suitable alternator, than trying to produce it from a system that's running at 14.1 volts maximum?

I appreciate  that not all vehicles have enough room under the bonnet to add an extra alternator, so the Ctec system would be a must, but aren't we talking about a Defender.. assuming that it hasn't got a Rolls Royce Merlin nestling under the bonnet, there is plenty of room for twin alternators and there are various kits available on the market for such an application. And having a twin setup there is, with the addition of a switched (isolator)  link, to have backup for the car's electrical system from the leisure system... Handy in the middle of nowhere.

At the end of the day, if your alternator fails on a Ctec setup, you are in hot water.. Not so with a twin setup..

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1 hour ago, miggit said:

I realise that there are different requirements from the battery types, but if you're using AGM for the leisure battery, surely it's easier to get 14.5 + volts from a suitable alternator, than trying to produce it from a system that's running at 14.1 volts maximum?

Even a normal leisure battery requires a different charging profile compared to a starter batter to most effective. Having a Ctek or similar unit allows you to swap out to a different type in future, with no wiring/alternator changes, as the price of the modern batteries come down. 

And no, creating a higher DC voltage is not difficult, finding different voltage regulators is definitely a challenge, as it is way out of the norm.

I see no reason for a twin alternator system, except for winch challenge type vehicles which draw hundreds of amps for a long period of time, and need as much juice back into the system as quickly as possible. They are often running 2, if not more starter type batteries in parallel, as well as supplying the winch with some of its requirement.

A second alternator, in a bush situation, is just something else to go wrong, and go wrong they do with dust and water crossings etc. A fully sealed, water/dustproof box that can sit inside the vehicle would be my choice for sure over something with moving parts.

 

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18 minutes ago, Bowie69 said:

A second alternator, in a bush situation, is just something else to go wrong, and go wrong they do with dust and water crossings etc. A fully sealed, water/dustproof box that can sit inside the vehicle would be my choice for sure over something with moving parts.

It is...but you're not avoiding having a failure prone alternator, you're just adding some redundancy. I've no opinion on what's the best solution in this case (no useful experience to bring to bear), but I can see where @miggit is coming from.

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Miggit - two alternators is not a simple fit on most vehicles, and then you've got non-standard belts/brackets and more load/weight for no real gain.

A relay costs a fiver (or £40 for an intelligent VSR version) and does a good enough job for almost everyone - most "leisure" and "starter" batteries, even AGM ones, have very little difference between them unless you go for something very specialised, certainly not enough to get excited about. Their charging profiles/specs are close enough as makes no difference as they know they're going to be hooked to an alternator in a car by 99% of customers.

My issue with CTek is for £300 they don't tell you what it's really doing at any given time - if it's being a bit smart and boosting the volts to try and get the full 20A into the battery or if it's just a solid-state version of a split-charge relay in a fancy box? Because, even with the added AGM function, I'm pretty sure that  £500 CTEK setup could be reproduced with about £30 worth of electronics.

Oh and in an emergency just swap/join the wires, why add extra switches and wiring "just in case", it's more things to go wrong... for a jump-start you can just short a spanner across the split relay terminals. If jump-starts are a regular occurrence, spend your money on sorting the problem out!

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^ what he said. For 10% the cost of a CTEK you can get something that perfoms 95% as well.

FWIW my solution is integrated into an arduino which monitors both batteries contents and chooses when to link or unlink the batteries (my own program), I also have a manual bypass switch for jumping or winch use.

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3 hours ago, Bowie69 said:

That, and the charging profiles for leisure and starter batteries are different, that's even before you have AGM, lithium or lead crystal batteries on board.

The Ctek boxes are proper battery management systems, not just a method of filling a bucket with water.

What charging profile are you talking about, please clarify. Lead-acid, AGM and deep cycle all use the same charging principle, constant voltage.

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Don’t forget that the Ctek unit we are talking about is a solar panel controller as well. It isn’t just replacing a vsr. (Yes I know there are cheaper controllers too). So two power source inputs and two outputs are available here. We also know that the main function is to lift the output voltages to whatever they need to be, independently of each other, thereby trying very hard to replenish the two batteries to 100%.

I don’t know why the Ctek unit can’t be trusted. After all many people are using their mains driven  smart chargers and finding that their batteries remain healthy for much longer than before. 

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4 hours ago, HoSS said:

What charging profile are you talking about, please clarify. Lead-acid, AGM and deep cycle all use the same charging principle, constant voltage.

Actually, they don't, to my understanding.

Starter batteries are more able to accept higher current than deep cycle, so for best efficiency you need to charge them differently.

I'm not going to try and reproduce stuff that is just a Google search away.
 

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Oops! I didn't mean for it to kick off.... 

I will admit that I was under the impression that the Ctec was the prefered solution, and at £500 ish, didn't appear to be more cost effective than a twin setup... however if you are saying just use a split charge relay / std h/d relay, even better!! It just appeared to be a very expensive solution to a cheap problem.

And surely if the batteries need a special form of charge an inverter / mains charger might be more flexible....

Oh and as far as different charge rate alternators go, try looking at the marine ones, I saw a sand alone regulator that was programmable for different battery types !

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14 minutes ago, Peaklander said:

I don’t know why the Ctek unit can’t be trusted. After all many people are using their mains driven  smart chargers and finding that their batteries remain healthy for much longer than before. 

It's not that I don't trust them to charge my battery, they appear quite well made, it's that I don't trust they're doing anything particularly clever for 10x the price of something else that will also charge my battery. They don't give much technical info, they don't display much beyond a couple of LED's, so you have to take their word that magic is happening.

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I've always wondered why the aux battery on mine was not terribly durable and the charge never lasts as long as I calculate that it should. Thanks to this thread now I know.

When we tour each year we use proper campsites rather than wild camping (mostly because we're all older and lazier and campsites have a bar and sit on toilets 😊). We don't go anywhere particularly remote or beyond reach of civilisation. 

The aux will last fine running the fridge for a night, but if we stay anywhere for 2 or 3 nights without driving then it doesn't last.

Conceivably then, I could live with my inefficient cheap and cheerful split charge system if I were to pay for a mains hook up and stick a mains charger on the aux overnight (the 240v on the fridge doesn't work but runs fine on 12v). In the morning the bacon won't have gone off and the water and beer for the day will be nice and cold and the aux battery will be tip top.

I don't really want to fork out for solar or new fancy batteries and management systems so this sounds a cost effective solution for me.

Anyone see any faults with that apart from a campsite with no hook ups ?

Mo

 

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