new battery time again

[wildebus]

I've checked a few up to the £280 mark and they all have charging current restrictions. This one https://www.alpha-batteries.co.uk/12v-leoch-pure-lead-carbon-plh-c100-deep-cycle-leisure-battery/ has a 30A limit and frankly looks like a superior battery to the cheaper Leoch ones.
The problem with adding resistance to the charging circuit to get you below 20A is that you've got to limit the 20A to when the battery is well discharged and as the battery charges the charge current will fall off meaning the charge time will rise. If you fitted a 20A B2B you'd get 20A continuous reducing the charge time considerably,

As the battery approaches fully charged, the charge current drops more and more and the final 20% or so will take a lot longer to get to full charge compared to say the time spent taken to take a battery from 50% to 70% SOC.

The chart that Victron gives up within the Smartphone App for their B2B to show the user what to expect shows this kind of sitution and is spot on.
The top line is Voltage and the bottom line is Current.

The charge phases of Bulk and Absoption can be - and are actually better - more accurately described as CC (Continuous Current) and CV (Continuous Voltage) mode, and the chart above illustrates that perfectly.

Personally speaking, I would not attempt to add resistance to the cabling to lower charge current as in reality you'd find the battery is the limiting factor in the first place (unless it is a very poor battery which demands a very slow charge rate)
Typically basic lead acid batteries have a charge rate of C/10 (10A per 100Ah) and better AGM and GEL batteries tend to go for around max of C/4 (25A per 100Ah).
This is where Lithium really excels where it will charge at a much higher rate of up to C1 from empty all the way to full with no dropoff (basically it charges in CC mode until full and then goes to float, bypassing CV mode)

allow £100 for the B2B plus the 115Ah LC battery and you're under £300, alternatively go for the one above and add enough resistance to keep charge rate at 30A at say 75% discharged, you'd get a reasonably fast recharge from the alternator.
Going back to LA will be cheaper but it probably wont last as long so you'll be swapping it sooner with all the extra hassle that goes with it, I guess it's pays your money and takes your choice.
Good luck with whatever you choose to do

 

[Harrytherid]

As the battery approaches fully charged, the charge current drops more and more and the final 20% or so will take a lot longer to get to full charge compared to say the time spent taken to take a battery from 50% to 70% SOC.

The chart that Victron gives up within the Smartphone App for their B2B to show the user what to expect shows this kind of sitution and is spot on.
The top line is Voltage and the bottom line is Current.
View attachment 133521
The charge phases of Bulk and Absoption can be - and are actually better - more accurately described as CC (Continuous Current) and CV (Continuous Voltage) mode, and the chart above illustrates that perfectly.

Personally speaking, I would not attempt to add resistance to the cabling to lower charge current as in reality you'd find the battery is the limiting factor in the first place (unless it is a very poor battery which demands a very slow charge rate)
Typically basic lead acid batteries have a charge rate of C/10 (10A per 100Ah) and better AGM and GEL batteries tend to go for around max of C/4 (25A per 100Ah).
This is where Lithium really excels where it will charge at a much higher rate of up to C1 from empty all the way to full with no dropoff (basically it charges in CC mode until full and then goes to float, bypassing CV mode)

So what you are saying, Dave, is that I would be quite safe to fit one pf those sub £200 LC batteries about which we have been talking.

 

[wildebus]

So what you are saying, Dave, is that I would be quite safe to fit one pf those sub £200 LC batteries about which we have been talking.

in terms of charging rates, I would not be concerned.

 

[Harrytherid]

in terms of charging rates, I would not be concerned.

so you are saying, Dave, that Merl is wrong to be so worried but do you have any other concerns that I should take heed of

 

[merl]

in terms of charging rates, I would not be concerned.

Woooo, interesting and surprising David
We know I =V/R
We know the alternator voltage and we know the battery voltage so we know V ( the difference between the 2.)
We know A mustn't exceed 20.and the only thing to stop that is R.
The battery's R when new is nowhere near enough but In a normal MH SCR and wiring setup there's loads of R but Harry has severely reduced his R with jump leads.
Just can't see how charge current can be below 20A into a brand new battery that's say 50% depleted. Just not enough R to stop it.
It'll be interesting for sure.

 

[Harrytherid]

Oh dear, oh dear, now what do I do, wait until you two come to an agreement, maybe. And I was hoping to have it up and running soon. Still; I still have the squeaking rooflight springs to sort out, any ideas? Fill the tubes full of lithium grease, I suppose, or replace the springs with shock cord; lads and lassies if you haven't got bored and stopped reading this thread that is.

 

[wildebus]

Woooo, interesting and surprising David
We know I =V/R
We know the alternator voltage and we know the battery voltage so we know V ( the difference between the 2.)
We know A mustn't exceed 20.and the only thing to stop that is R.
The battery's R when new is nowhere near enough but In a normal MH SCR and wiring setup there's loads of R but Harry has severely reduced his R with jump leads.
Just can't see how charge current can be below 20A into a brand new battery that's say 50% depleted. Just not enough R to stop it.
It'll be interesting for sure.

All I can say is I have watched the current into batteries and with Lead it is very rarely limited by the charger or Alternator even with running cables that are more than capable of delivering high current. That leads me to one conclusion ... Batteries!

Now as far as not charging more than 20A, I thought this was the battery being discussed? https://www.alpha-batteries.co.uk/12v-leoch-pure-lead-carbon-plh-c100-deep-cycle-leisure-battery/
In the datasheet, it quotes a charge current of 30A, which is around what I would expect for good 100Ah Lead battery.
Apart from anything else, I would also install a B2B for optimum charge profiles anyway and for a 100AH battery I would go for a 30A unit which happens to be a good match for that battery.

PS. Jump Leads are rubbish cables. People think they are big fat cables but when you look at them they are not, they just have very thick insulation to a) give the appearance of heavy cables and b) heat insulation for the user and c) make sure no shorting as laying against car metalwork.
I just chopped the end of a jumper lead set to show what I mean ....
The faded Red & Black pair are the jumper cables and the brighter red cable above is a 35mm2 cable

IMG_20240726_171608_653 by David, on Flickr

Look at the actual cable here after removing the insulation .... that cable slides easily into a 10mm2 ring terminal!

IMG_20240726_171600_922 by David, on Flickr

(I suppose it does depend what you think are heavy cables? anything under 25mm is light to me. I'd use 10mm2 cable for a 12V Compressor Fridge).

 

[merl]

Now as far as not charging more than 20A, I thought this was the battery being discussed? https://www.alpha-batteries.co.uk/12v-leoch-pure-lead-carbon-plh-c100-deep-cycle-leisure-battery/
In the datasheet, it quotes a charge current of 30A, which is around what I would expect for good 100Ah Lead battery.

That's the wrong one David, it's the cheaper version with a link in post 63, spec says max charge is 0.25 C and the top label confirms 21.6A.
I understand your point re cheap jump leads being crap, Harry's could be even crapper and be aluminium! BUT they may not, he may have used a set from 1957 ( the best year we both agree on that) when they made proper jump leads!
And if not 6m or so of crappy 10mm ain't enough R to get below 20A according to my way of thinking anyway.
Ultimately he needs R.
If, like you say there's enough R in the cables and battery well Harry's fine and dandy. If not he'll simply have to add some, simples.
Fit the battery which should come pretty much full, start the engine and monitor the current.
Take out 10% which will be simple enough to calculate because Harry has a DC clamp meter and re test the charge current again, repeat till either he gets to say 70% discharged and 20A is still isn't exceeded or he reaches the limit. If that happens it'll be easy enough to calculate the required extra cable if Harry measures the battery and alternator voltages at each stage.

 

[wildebus]

so you are saying, Dave, that Merl is wrong to be so worried but do you have any other concerns that I should take heed of

All I am saying is me personally would not worry based on what I have seen on my own setups. I am not recommending anything or stating anything other than that in this discussion.

 

[trevskoda]

David i used a proper battery cable to link all my less batts up, and also from the relay in, yes some el cheepo jump leads are just junk, however working on cars i many years back bought a very heavy duty copper set used in the trade, and even back then there were well over £20.

 

[Harrytherid]

I will have to read this lot again in the morning after a good nights sleep cos it has just fuddled the poor old head and I hardly know which way is up
now,

 

[Pudsey Bear]

It's all work of the Devil Harry and I sympathise greatly.

I always try to keep things as simple as possible and easily available and cheap, don't forget cheap.

 

[Harrytherid]

Right lads, firstly those cables are copper not copper clad aluminium (microscopic inspection of cut ends). They are new Halfords jump leads. The cross sectional area of the conductors is 6.75mm not measured by miking individual wires but tightly twisting and miking whole lot at once so probably 5 sq. mm in reality.

The layout is.... lead taken from plus side of starter battery through 50A fuse (could easily reduce that to 20A.) to SCR to manual battery isolating switch then to battery as instructed by installation directions of SCR; though isolating switch is optional and is my personal choice after burn out disaster which is probable cause of battery failure though it would not have prevented that problem.

To get the required R how much of and what size cables would you recommend. Is there not a suitable resistor I could get? and if I go to lead acid what is the best low maintenance battery I should buy.

 

[Harrytherid]

Why did it take me so long to reply? I wrote it yesterday morning first thing but for got to post it and kept wondering why no replies till last thing at night I looked again and twigged the non posting; silly me!

 

[merl]

It's all work of the Devil Harry and I sympathise greatly.

I always try to keep things as simple as possible and easily available and cheap, don't forget cheap.

It's actually all boils down to or as I like to view it

Right lads, firstly those cables are copper not copper clad aluminium (microscopic inspection of cut ends). They are new Halfords jump leads. The cross sectional area of the conductors is 6.75mm not measured by miking individual wires but tightly twisting and miking whole lot at once so probably 5 sq. mm in reality.

The layout is.... lead taken from plus side of starter battery through 50A fuse (could easily reduce that to 20A.) to SCR to manual battery isolating switch then to battery as instructed by installation directions of SCR; though isolating switch is optional and is my personal choice after burn out disaster which is probable cause of battery failure though it would not have prevented that problem.

To get the required R how much of and what size cables would you recommend. Is there not a suitable resistor I could get? and if I go to lead acid what is the best low maintenance battery I should buy.

That's good info re the cables etc but tbh there's still too many variables and unknowns to know exactly how much more R you'll need at this stage, when you get the battery it'll be possible to make some measurements and calculations and establish what's needed. It may be possible to use a fixed resistor but it'll possibly generate a lot of heat (depending on what value you need) so you'll have to start bolting it to a heatsink which is a faff, as I've already mentioned it would be best to use extra cable, this would spread the heat and more importantly would be infinitely variable and tweakable.
WRT adding extra cable, I'd use whatever I'd got to hand, it needs to be 1.5mm guage minimum but if you'd got some 1mm you could double it up.

Sorry but can't help you with LA leisure battery recommendations , I have no useful experience of using them. Ask 100 people and you'd get about 100 different answers I guess. Lots of folk just buy the cheapest and swap regularly, of course this is something you'd like to avoid.

 

[Harrytherid]

Thanks Merl, I shall have to suck it and see with the LA battery. Still not sure which way to go. Mate of mine is keen on LA so I shall ask him.

 

[merl]

Thanks Merl, I shall have to suck it and see with the LA battery. Still not sure which way to go. Mate of mine is keen on LA so I shall ask him.

You seem pretty capable but if you get stuck I'm not far from you whenever you make the trip next time to your daughter's, I'm just off j22 of the M1. If you're going to scraptoft I'll see you there

 

[Harrytherid]

Hi Merl. I shall probably come over when nearby just to touch base. Always handy to have somewhere or someone to see when the women have children to occupy them. I will give you a shout when I know I shall be up there. Meetings are not Julie's thing so I am unlikely to go to Scraptoft

 

[Harrytherid]

Well I got cheapish glass matt leisure (or so it claims) battery...130AH at sub £100 and it went in OK. I wired it up it and tested it with a 20a fuse on which I placed a bead of water as a telltale in case of heating up, it stayed cool enough not to boil bead of water. Ran the engine and all OK and meter showing 10A reducing to 9A after a couple of minutes so I coated the fuse in beeswax which I would smell if it got too hot and went for a drive. Hit 70 and no smell so all apparently OK. Could not look at meter while driving, of course, so can only hope all is OK.



Time will tell and I have plenty of fuses and the one in place is still coated in beeswax. Now back on EHU so will stay charged. In the morning I shall take it off EHU and will see if it stays up after a few days.

 

[merl]

Well I got cheapish glass matt leisure (or so it claims) battery...130AH at sub £100 and it went in OK. I wired it up it and tested it with a 20a fuse on which I placed a bead of water as a telltale in case of heating up, it stayed cool enough not to boil bead of water. Ran the engine and all OK and meter showing 10A reducing to 9A after a couple of minutes so I coated the fuse in beeswax which I would smell if it got too hot and went for a drive. Hit 70 and no smell so all apparently OK. Could not look at meter while driving, of course, so can only hope all is OK.



Time will tell and I have plenty of fuses and the one in place is still coated in beeswax. Now back on EHU so will stay charged. In the morning I shall take it off EHU and will see if it stays up after a few days.

You will have installed a pretty much fully charged battery because that's how they are stored and supplied. Charge current into a full battery slows right down. The acid test will be when the battery has been used and discharged by a decent level, expect the charge current from the alternator to be considerably higher at that point, as I've already said considerably higher than 20A.
A 20A fuse will stand 30A for a long time but will get quite warm. 20A fuse wont rupure quickly until your at say 40 or even 50 amps but a lot will depend on the quality of the fuse, I've had budget brand blade fuses that are way over spec and completely inaccurate.