Leisure Battery, split charge relay advice please...

[g8dhe]

The instructions said to disconnect the battery before charging it, but I didn't fancy the hassle so didn't bother. Is there a reason why you should?

Yep, the can't be considered liable if anything goes wrong, also if there is any siginifcant load then it won't be charging the battery in the way it thinks it is, I noticed in the manual that it claimed to be what's called a 3 phase charger (No nothing to do with 3 phase mains supplies), the two later phases in most 3 phase chargers measure voltage and current to decide when to change modes - if your drawing current whilst charging it will get it wrong.

Also, it says not to use the charger below 0 degrees Centigrade but I risked that too as car was next to house. Why do they advise this though I wonder, and do both the above have implications for on site re-charging and/or winter camping?

One phase of charging will be done at the highest voltage normally limited to 14.7 Volts exceeding this WILL damage a battery, it could be that as temperature decreases the accuracy of the charging voltage might change and exceed this (it could also decrease in which case that isn't a concern).

I'm still suspicious my LB is down on AmpHr condition but is there any ready way to check it (maybe using a shunt and voltmeter?).

Yes fully charge the battery, then draw a fixed current until the voltage drops to the safe limit (nominally 11.9 Vots is fully discharged some will go lower but don't count on it! or 2.1 volts per cell for an SLA) the number of hours times the current drawn is the AmpHr capacity.

I noticed they are now quoting starter battery power in cranking amps (e.g. 680amps was high power). Is there any way I can work out AmpHr rating from that

No.

[mikeonb4c]

Fantastic Geoff. Really useful advice (and pretty much what I suspected).

I'm not too bright on these things. I have a multimeter but have never used it to measure current. Do you happen to know how you do that? I have an in-car voltmeter wired up to show LB voltage so that is taken care of.

Incidentally, this has all come about because my LB seemed unable to provide a current (a guess here) of 8 amps for a 12v electric blanket, without its voltage dropping to the point of triggering a 11.5v low voltage cutout. It seems odd it can't do that although it can run other lower current stuff OK. Is the battery duff I wonder, or do LB's not like delivering more than a limited current.

Naughty Halfords trying to hide behind cranking amps

[francophile1947]

or do LB's not like delivering more than a limited current.

Naughty Halfords trying to hide behind cranking amps

It's been said many times Mike - LBs cannot deliver a high rate of discharge. They are purely designed to give a low output for a long time. They have fewer, thicker plates, with a low surface area, so they can only carry out the necessary chemical reaction slowly
Halford's aren't hiding anything. Even a low Amp/Hr battery can have a high cranking power - it's all down to the interior design (see my reply to your previous post at the bottom of page 3). More plates will give a higher surface area and allow a very fast discharge.

[mikeonb4c]

or do LB's not like delivering more than a limited current.

Naughty Halfords trying to hide behind cranking amps

It's been said many times Mike - LBs cannot deliver a high rate of discharge. They are purely designed to give a low output for a long time. They have fewer, thicker plates, with a low surface area, so they can only carry out the necessary chemical reaction slowly
Halford's aren't hiding anything. Even a low Amp/Hr battery can have a high cranking power - it's all down to the interior design (see my reply to your previous post at the bottom of page 3). More plates will give a higher surface area and allow a very fast discharge.

And I've noted it many times before you old dog! But I can't immediately recall anyone giving an actual figure. My suspicion is the current being drawn by the electric blanket is not more than about 8 amps which, times 12v to give wattage doesn't in my view amount to a particularly demand on the battery (96 watts?). So what's going on? Do I have a duff battery or can an LB not service a current of 8 amps?

Even a low Amp/Hr battery can have a high cranking power

QED - Halfords are not telling us the Amp/Hr. I reckon this could be significant in terms of how well the battery copes with a car that is reluctant to start or if - as in my case - I want an indicator of its total energy holding capacity.

[francophile1947]

And I've noted it many times before you old dog! But I can't immediately recall anyone giving an actual figure. My suspicion is the current being drawn by the electric blanket is not more than about 8 amps which, times 12v to give wattage doesn't in my view amount to a particularly demand on the battery (96 watts?). So what's going on? Do I have a duff battery or can an LB not service a current of 8 amps?

Even a low Amp/Hr battery can have a high cranking power

QED - Halfords are not telling us the Amp/Hr. I reckon this could be significant in terms of how well the battery copes with a car that is reluctant to start or if - as in my case - I want an indicator of its total energy holding capacity.

Old dog I don't think there can be a specific figure - it all depends on the way the particular battery is constructed. I feel pretty sure that 8A is too high a discharge rate for most LBs to match for any length of time. Would be OK with one of those hybrid leisure/starter batteries.
The Amp/Hr is largely irrelevant with a starter battery. It was more essential in the old days when most cars were a b*gger to start, but they usually fire up straight away nowadays so a high cranking rate is more important than actual capacity. Of course, it's no help at all when you've got duff glow plugs

[mikeonb4c]

Thanks John. Ignore the 'old dog' remark - just my sense of humour. I speak as one old dog to another

[francophile1947]

Thanks John. Ignore the 'old dog' remark - just my sense of humour. I speak as one old dog to another

I did ignore it Mike - hence the smilies after my reply. I reckon we would both know if we meant to be snotty

[g8dhe]

I have a multimeter but have never used it to measure current. Do you happen to know how you do that? I have an in-car voltmeter wired up to show LB voltage so that is taken care of.

OK, your going to need two (2) meters one to measure the voltage whilst the load is connected and the second to measure the load current both reasonably accurate ( a dashboard analogue meter for the voltage is NOT suitable) - you can do this with one meter but its going to mean a lot of swapping around every hour for between 20 and 30 hours ......

Next thing before you get round to the mutimeter is do you have a suitable load to discharge the battery with ?
I would suggest that a car bulb of around the sort of current you expect to draw on average would be a reasonable starting point so if say 4 Amps on average is your load then a headlight bulb of about 48-50 watts (Wattge/volts=Amps =48/12=4Amps) would about right.

The next thing is take the battery out of the vehicle, or at least disconnect the +Ve lead for the duration of the testing i.e. if your battery is rated at 80AmpHrs and your drawing 4Amps then its going to take about 20 Hours.
Next make sure the battery is fully charged, use the new charger and let it give a complete charge of at least 24Hrs and no harm to charge it for 48Hrs (or longer) at all.
You will need to be able to connect the multimeter in series with the bulb to measure the current and so your multimeter will need to be able to handle that current (A lot of them will be rated to measure 10A).
To select the right range on the M/M (multimeter) will involve the rotary switch and also very often swapping the leads between different sockets on the M/M. You wil set the rotary switch to highest current range and then plug the lead into a second socket, in this meter from Maplin you would select 10Amps and then use the socket associated with that range marked 10Amps
The positive lead of the current meter will go to the battery +ve, the Negative lead will connect to the bulb and the other bulb connection will go to the battery -Ve. You need to be able to make these connections securely and reliably, you won't be holding the meter leads on by hand ! The voltage meter will simply be connected to the battery +ve and -Ve terminals directly.
NOTE the current meter will have a fuse inside it and if you miss connect the meter then there is a good chance you will blow the internal fuse.
Final thing is you will need a note book and pencil to log the current readings EACH HOUR.
So connect up as outlined above, and note the Voltage and Current, leave the circuit connected, an hour later read the Voltage and Current again, repeat hourly until the Voltage has fallen to 11.9 Volts or if you wish to push your luck and possibly knacker the battery continue until it reads 11.5 Volts, less than this and you will be able to chuck the battery way afterwards !
Finally at the end then all you need do is add up the Current coloumn for every hour, the total will be the capcity of the battery.
Point to note if the temperature is low then the batteries capacity will be reduced. In sub-zero temperatures then by as much as 20-50+% can be lost.

Incidentally, this has all come about because my LB seemed unable to provide a current (a guess here) of 8 amps for a 12v electric blanket, without its voltage dropping to the point of triggering a 11.5v low voltage cutout. Is the battery duff I wonder, or do LB's not like delivering more than a limited current.

Where was the the sensing voltage relay / device, if it was beside the heater then I'm not suprised, you won't have been measuring the on-load battery voltage, you will have been measuring the voltage at the end of a long lead! You really need to have a single device AT THE BATTERY TERMINALS which will disconnect the battery once it has dropped below 11.9 / 11.5 volts. It wouldn't suprise me to find that you have a volt drop of at least 1 volt between terminals and device @ 8 Amps.

Naughty Halfords trying to hide behind cranking amps

To be fair it is the Cranking Current which is important for starting, these days the alternators will handle the internal running load no problem as well as the charging load. So that is what they quote. If the battery was quoted as being for a leisure battery then they will have quoted the Capacity, but the individual figures on there own are never enough to give you all you need to know.

[g8dhe]

Just noticed that while I wrote the above the times were based on getting the full capacity out of the battery, that you won't do without knackering it, about 50% is the normal limit so where I suggested 20-30 hours it should read 10-15 hours etc.

[mikeonb4c]

Thanks Geoff. That is really a fantastic advisory post. Too good to be just left there, it should be a BF factsheet (any moderators able to advise on how to do that - titled 'Testing your Leisure Battery'). I shall be saving it for further reference in any case! the multimeter looks exactly like mine, and all you say makes sense (even if the voltage drop issue does pose a problem - I do have a long lead to the blanket but its weird that the 75AmpHr starter battery I did initial tests with didnt lead to a voltage drop yet the 110AmpHr LB did).

Thanks+++ again.

Mike

PS - I'm worried the LB may be knackered as it did suffer heavy discharge once in 2007 from coolbox use and because the VSR protective fuse blew due to heavy charging current after that and I didn't have a voltmeter (digital) fitted at that time so didn't notice it was not receiving charge, it remained discharged for at least a week. On the other hand, we are told that LBs are relatively tolerant of that

[francophile1947]

its weird that the 75AmpHr starter battery I did initial tests with didnt lead to a voltage drop yet the 110AmpHr LB did).


PS - I'm worried the LB may be knackered as it did suffer heavy discharge once in 2007 from coolbox use and because the VSR protective fuse blew due to heavy charging current after that and I didn't have a voltmeter (digital) fitted at that time so didn't notice it was not receiving charge, it remained discharged for at least a week. On the other hand, we are told that LBs are relatively tolerant of that

Probably just because the LB couldn't convert enough power to meet the demand. Voltage would probably have gone up again after a few minutes resting.
LB may just need a good charge - leave it connected to your Lidl charger for a couple of days.

[mikeonb4c]

its weird that the 75AmpHr starter battery I did initial tests with didnt lead to a voltage drop yet the 110AmpHr LB did).


PS - I'm worried the LB may be knackered as it did suffer heavy discharge once in 2007 from coolbox use and because the VSR protective fuse blew due to heavy charging current after that and I didn't have a voltmeter (digital) fitted at that time so didn't notice it was not receiving charge, it remained discharged for at least a week. On the other hand, we are told that LBs are relatively tolerant of that

Probably just because the LB couldn't convert enough power to meet the demand. Voltage would probably have gone up again after a few minutes resting.
LB may just need a good charge - leave it connected to your Lidl charger for a couple of days.

I reckon that's about right. As a result of this debate and advice as above I can now set up an interesting test regime to try and understand what makes my LB tick (well not literally!). We really should save this advice from Geoff as a factsheet doncha think John? Anyone got delegated power to do that as a moderator?

[g8dhe]

You might find this write-up of some help, its primarily intended for Starter Batteries but the basic facts remain the same;
What causes car batteries to fail?

[francophile1947]

We really should save this advice from Geoff as a factsheet doncha think John?

No idea Mike - I didn't understand a word of it My multimeter sits in the cupboard until I pluck up courage to read (and hopefully understand) the instructions