Battery life expectancy

[Ferrodo]

Hi all, hope everyone is well and looking forward to another caravaning season.
We bought our Swift in 2016 brand new complete with a brand new battery and it’s still doing the business. Holds 12.6 volts when not on charge by either the charger or solar panel and there’s no indication of it struggling with anything as in the movers etc. So nine years old ….. should I change it for new as a preventative maintenance measure or just let it carry on? Can’t make up my mind. Opinions will be appreciated.
My best regards all
F

 

[ProfJohnL]

"If it ain't broke don't fix it" comes to mind. If the battery is holding a standing charge of 12.6,V dc, that does suggest its doing quite well. Its unlikely to suddenly collapse leaving you with no power, so just keep a watching brief and when it starts to only hold 12.4V after charging, that might be the time to think about a replacement battery.

Or if you can get hold of a multi stage charger (e.g. Ctek or Mobo, etc.) get one with a "reconditioning" programme and see if that rejuvenates for a while longer.

 

[Ferrodo]

Prof, I have a ctek with the recon facility but I must admit after nine years if it did start to struggle then I would change it ….. it doesn’t really owe me anything. We rarely go off grid so mainly on hook up. Suck it and see I think then. Impressive life span though

 

[ProfJohnL]

I agree, the fact you tend to use EHU sites means you barely need a battery. In fact if and when the battery does collapse, then you don't need to change it for a full sized leisure caravan battery. A considerably smaller and cheaper car battery would provide all the capacity you need for even using a caravan mover. Just make sure a smaller battery is properly secured in the battery box so it cant move around when traveling.

 

[Ferrodo]

Thanks Prof. When this battery finally does turn up its terminals I will replace it with another 100A/H for no other reason then I like to know that I have the reserves of sparks should I need. A sobering thought is that the next battery will probably be the last one I buy in this life. 😉

 

[Oscarmax]

I agree, the fact you tend to use EHU sites means you barely need a battery. In fact if and when the battery does collapse, then you don't need to change it for a full sized leisure caravan battery. A considerably smaller and cheaper car battery would provide all the capacity you need for even using a caravan mover. Just make sure a smaller battery is properly secured in the battery box so it cant move around when traveling.

When we changed our 110 amp battery to a Fogstar 105 amp lithium battery I was surprised how much smaller the battery was, we used the packaging supplied with the Fogstar battery to safely secure the battery.

 

[Hutch]

Being a bit long in the tooth now and Mrs H's health deteriorating, changing our battery to a lipo is not really an option.
Reasons
1 us and how much longer to caravan.
2. Caravan is a 2013 Coachman, would the charger be suitable.
3 . we normally do just EHU.

If your battery is working, don't change it just be ready when you go away to buy a new one. 4 hours without pow , not a problem.

 

[Ferrodo]

Being a bit long in the tooth now and Mrs H's health deteriorating, changing our battery to a lipo is not really an option.
Reasons
1 us and how much longer to caravan.
2. Caravan is a 2013 Coachman, would the charger be suitable.
3 . we normally do just EHU.

If your battery is working, don't change it just be ready when you go away to buy a new one. 4 hours without pow , not a problem.

I’m with you on lithium…. Can’t really justify the expanse plus I am not convinced that the standard Swift charger would be suitable.

 

[borderbilly]

As prof says, a small car battery. I got one from the scrappies for £14 and it lasted years.

 

[trevormonty]

As side note I've tested 9AH LiFeP04 motorbike battery with MM, had no problems moving caravan. Also used it to jump start car. Rated for 400A of cranking current, not bad for battery that weighs about 1kg.

Good alternative to 28kg 100AH AGM if you only need it for MM. I charge it from simple 1A lead acid battery charger, caravans built in charger would be to much for it.

 

[IanB1485]

built in charger would be to much for it.

No it wouldn't as the charge voltage rises the current delivered to the battery drops. even a small A.hr battery only takes what it needs to change the chemicals inside it and as they change the battery voltage rises and the supplied current drops away to zero it justs takes a shorter time than for a bigger A.hr battery. Some chargers state the maximum size of battery as its the charger thats not up to it as it may overheat certain components within the charger.

 

[ProfJohnL]

When we changed our 110 amp battery to a Fogstar 105 amp lithium battery I was surprised how much smaller the battery was, we used the packaging supplied with the Fogstar battery to safely secure the battery.

The reason I suggested considering a smaller battery, was not for its physical size and weight (even though that could be a bonus) it was becasue if you are always using EHU, you don't use all the charge capacity of a big (and expensive) Leisure battery.

In fact with modern caravans (since about 1985) have been fitted with switch mode power supplies (SMPS) rather than simple battery chargers, and in fact with the exception of a caravan mover, in most cases you can safely run the caravan without a battery.

In the early years of SMPS's the manufacturers were a bit stingy and only fitted units with 8Amps output and some water pumps struggled to start, but these days most caravan supplies have 12 to 16A and again apart from the caravan mover these can handle all the caravans 12V needs without a battery!

Where a caravan mover is required, or they may be a need to have a permanent 12V feed for an alarm or volatile memories of radio's you may still need to fit a 12V battery of some kind. But contrary to the common perception caravan movers don't use a lot of energy (=kWh) and so they don't need a large caravan battery.

What caravan movers need is a battery that can deliver about 100Amps of current for a a second or two after which the movers current draw drops significantly as the motors spool up. Typical running currents of movers are in the low tens of Amps, it will only increase if the caravan is being moved up a hill or can't climb over an object, for example a tall kerb or stone.

When you look at the way a typical caravanner uses a motor mover its actual time running is likely to be less than 5 min. Even if it were 5Min that's only 1/12 of an hour which means it average current draw lets say 30A (15A a side) means it only consumes 2.5 Ah of the batteries capacity, and it would be typically less than that. Consequently most small car batteries are quite capable of this.

And of course once the caravan is sited and the EHU plugged in the battery will be recharged keeping it in good condition.

 

[JTQ]

Using your mover is likely to be where the battery will initially announce it has had its day. Unfortunately, that can sometimes be when you really need it, it would be in my case as accessing my property from the lane the mover is essential. If I fail half way where the climb starts the lane is blocked. I have it wired up so I use a battery kept at home always on charge to partially cover that risk.

If the mover's use would not be a show stopper, I would agree with previous posts, wait till there is a need to change it. Clearly the one you have and the charging system together with your usage are a good combination. I understood Swift did fit some "Smart technology" chargers around yours' era, that would be very good for battery longevity.
-----------------------------------------------

A side question for those that better understand electronics. Does the now near universal "soft start" in mover technology not reflect in significantly reduced starting current draw, relative to the early abrupt starting type? The physics would suggest so, but is any gain there just pumped into heating up the electronic bits?

 

[Gafferbill]

......I once ran a caravan battery up past 8 years old and it went from seemingly OK to useless in the course of an hour.
It was being charged by the caravan charger and started venting gas, bubbling and getting hot.
One knackered battery!
The caravan didn't have a mover which I'm sure would of found the battery to be failing earlier.

If I was the OP I would replace the battery.

 

[JTQ]

Gaffer's failure seems like a plate short, paste dropping out across adjacent plates, can happen anytime, bouncing along the road being ideal cause
Charging system trying to treat a now 10 volt battery as a 12.

 

[trevormonty]

Using your mover is likely to be where the battery will initially announce it has had its day. Unfortunately, that can sometimes be when you really need it, it would be in my case as accessing my property from the lane the mover is essential. If I fail half way where the climb starts the lane is blocked. I have it wired up so I use a battery kept at home always on charge to partially cover that risk.

If the mover's use would not be a show stopper, I would agree with previous posts, wait till there is a need to change it. Clearly the one you have and the charging system together with your usage are a good combination. I understood Swift did fit some "Smart technology" chargers around yours' era, that would be very good for battery longevity.
-----------------------------------------------

A side question for those that better understand electronics. Does the now near universal "soft start" in mover technology not reflect in significantly reduced starting current draw, relative to the early abrupt starting type? The physics would suggest so, but is any gain there just pumped into heating up the electronic bits?

Should reduce initial draw as stopped motor looks like dead short. Ramping voltage up over few seconds means minimum current is needed to start it moving. Motor speed control is done by PWM (pulse width modulation), switch power on and off very quickly eg 10khz. Eg 50% would be ON for 50us (microsecond) then OFF for 50us. This results in average voltage of 6V but torque is lot higher than if you apply just 6V as motor see 12v for short periods. This why PWM is excellent way to control motor speed. The only losses/heat buildup in electronics is from slight resistance across transistors when ON eg 0.1 Ohmn, and voltage ramp from OFF/ON/OFF transition.

 

[JTQ]

Thanks "trevor" for the clearly presented logic which I can follow and understand.
I had convinced myself that given the low mass of the componentry in the electronics, no large levels of electrical power could possibly be converted to heat there, so clearly there was something smarter happening. Thanks, John

 

[trevormonty]

No it wouldn't as the charge voltage rises the current delivered to the battery drops. even a small A.hr battery only takes what it needs to change the chemicals inside it and as they change the battery voltage rises and the supplied current drops away to zero it justs takes a shorter time than for a bigger A.hr battery. Some chargers state the maximum size of battery as its the charger thats not up to it as it may overheat certain components within the charger.

The 9AH LiFepP04 motorbike battery specifically says 10A max charge. All batteries have max charge current, which can be exceeded it charger can deliver current. Exceeding it will over heat battery and cause it to vent as chemistry can't absorb gases generated quick enough.

 

[ProfJohnL]

The 9AH LiFepP04 motorbike battery specifically says 10A max charge. All batteries have max charge current, which can be exceeded it charger can deliver current. Exceeding it will over heat battery and cause it to vent as chemistry can't absorb gases generated quick enough.

The description I provided in #12 was for a LA car type battery. Such batteries could see an alternator output of 60A to recharge the battery, so they would not troubled by the 16 to 20A of a caravan charger.

If anyone wanted to use a LiFepP04 battery on a caravan, they must check the chargers compatibility with the batter chemistry. Part of that check should of course include the batteries compatibility with the chargers maximum output.

It would be irresponsible to fit an incompatible battery to a caravan, so your scenario of potentially exceeding the maximum charge rate should never ever occur.

However if such a scenario did arise, the fact that modern caravan chargers have good voltage regulation that will prevent excess voltage from being generated, the current fed into a battery to charge it will be limited by the batteries impendence at any given state of charge.

Consequently the current fed to a battery as it charges does reduce as the state of charge increases. I am not sufficiently aware of the standing voltage characteristics of LiFepP04 chemistries, but based on the 9Ah LiFepP04 scenario having used about 2.5Ah of charge for the mover state of charge will be circa 72% or more, and I seriously doubt the charger could deliver its full charge rate into that battery.

Don't take from my comment that I think such a small capacity battery would be a sensible choice, I suggested a small car battery which is likely to 30 Ah LA or more.

 

[Oscarmax]

If anyone wanted to use a LiFepP04 battery on a caravan, they must check the chargers compatibility with the batter chemistry. Part of that check should of course include the batteries compatibility with the chargers maximum output.

I take it you intend on deep frying it then

 

[ProfJohnL]

I take it you intend on deep frying it then

I depends if you like the flavour or not

 

[Oscarmax]

A bit like battered mars bars

 

[IanB1485]

A side question for those that better understand electronics. Does the now near universal "soft start" in mover technology not reflect in significantly reduced starting current draw, relative to the early abrupt starting type? The physics would suggest so, but is any gain there just pumped into heating up the electronic bits?

I've worked with lots of motors in my professional career (D.C,AC single and 3 phase, stepper types,induction e.t.c ) so I think can answer that. The transistors that control the motors are switched on and off at high speed , the basic physics is that when off the transistor has lots of volts across it but no current flow , so no power is dissipated within the transistor, conversely when ON there are lots of amps flowing ,but the 'ON' voltage across the transistor is low , typically as low as 0.2V for modern MOSFET types so again the power dissipation in the transistor is also low ( 10A x0.2V = 2W) the main power loss comes whilst the transistor is transitioning from OFF to ON. The faster the transistor switches (100ns is common) the lower the power dissipation . The initial motor current when fed through a simple relay is high as the magnetic field in the rotor is built up, by using a pulse width modulation principle and gradually increasing the ON period , this initial inrush of current is avoided . As a side point all new motors above 375W ( I think thats the value) now have to be soft start , so even your humble circulation pump in your house may be a soft start type,
So the short answer is no , the heat build up is minimal , the second advantage is that by not using conventional relays ( other than to change direction) the life of the system should be higher.A further advantage is that the cable sizes can be smaller as there is no big in-rush of current which with thinner cables leads to significant voltage drop in the cables.

 

[ProfJohnL]

The initial motor current when fed through a simple relay is high as the magnetic field in the rotor is built up, by using a pulse width modulation principle and gradually increasing the ON period , this initial inrush of current is avoided .

This is not quite right.

Soft start in terms of a caravan mover is implemented not to reduce the demand on the supply battery but to make the movement of the caravan more controllable for close proximity positioning.

There are several ways in which soft start can be implemented, but I will concentrate on the scheme you have suggested, and hopefully explain why your description is not quite right.

With the presumption the switching transistors/mosfets that are being used to create a soft start are transitioning much faster than the pulse width switching frequency, For the duration of any ON period the full supply voltage will be applied to the motors brushes, and consequently the stationary motor will draw the full current for the duration of the pulse width.

The effect of that inrush current is to begin to build up the electromagnetic magnetic field within the motor which it cannot complete instantly, and equally when the pulse is in it off period the magnetic field also takes somewhat longer to decay so successive pulses build up the magnetic flux and thus its torque, in the motor. The torque has to increase to the point where it can over come all the frictions and loads and begins to spin the motors shaft.

As soon as the motors shaft is rotating, the magnetic fields of the motor interact differently and the motor produces a back EMF which reduces the supply voltage delta and opposes some of the input current reducing the amount of current the motor consumes.

Because the soft start pulse width reduces the power (not current) delivered to motor over time, the duration of the current pulses puts less cumulative stress on the battery, and it might mean a battery with a lower peak current capacity might have time enough to recover from the peak load before the next pulse arrives. Its likely the battery (in terms of cold cranking amps) will not last as long as a correctly sized battery.

 

[Ferrodo]

Too clever by far this lot…. I bet they even know what wood is made from 🤔