Smallest amp capacity 12v battery for caravan.

[Anseo]

Part way into completing a project and I am trying to determine what is the smallest amp hour capacity 12v battery I can put in a caravan for use when on electric hook up.

The main purpose of this battery is to smooth out ac generated 12v power.

Devices that will require 12v DC supply are:
Caravan control panel, lighting, heating system blown air fan, water pump, fridge light, toilet flush, gas oven\cooker igniter, on-board fitted radio and antenna signal booster; I may have missed some things out from the list , I won't be powering a motor mover.

I will not require spare amperage capacity in the battery for an event such as a power outage.

So how low an amperage is feasible for a" smoothing " battery, would a battery capacity of 50 Ah or 40 Ah or even 12 Ah meet the task?

Target is for the lightest weight LA\AGM\GEL battery I can practically use.

 

[ProfJohnL]

Unless your present caravan 12V system was made before about 2000, it will already use a Switch Mode Power Supply (SMPS) which will produce at least 8A, or possibly 12A of smoothed 13.8V dc, and a few were even rated to 16A. These were in general capable of running the loads you have described without a 12V battery. The 12V battery was only necessary if the caravan was being used off grid.

However some caravans used inboard water pumps some of which had quite larger starting currents, and when they turned on the pulse of current they needed to get the pump turning cold cause momentary drops in the 12V wiring which could upset other appliances that were switched on. If that occured, fitting a 12V battery easily cured it.

I would suggest If you already have at least an 8A SMPS fitted as standard try using the caravan and see if you have any problems. If its OK then its saved you the cost and weight of a battery.

If on the other hand you seem to have any problems, then I suspect you might get away with 12ah gel battery, but certainly a 20Ah or bigger should do the trick.

 

[Woodentop]

If the caravan is always used on EHU then in theory it does not need a battery <but> you need to fit one, not to smooth out the supply, but more to supply the (sometimes high) current demanded by some items still running on 12V. The obvious one is an internal water pump which may only take a couple of amps when running but the draw for a fraction of a second at start could be several times that. <That> is more what a caravan battery is for.

 

[Anseo]

If you fit a Victron Charger you don't need a battery it has a smoothed PSU mode.

Blue Smart IP22 Charger - Victron Energy

The Blue Smart IP22 Charger is the new professional battery charger with built-in bluetooth. Find a Victron Energy dealer near you.

www.victronenergy.com

I already own a Victron Blue Smart IP22 Charger 12/30(1) 230v.

I know what functions these devices are able to perform.

Such a unit has no benefit or other usable attribute in my ongoing project.

Aware that threads can and often do go adrift, I was I think quite careful in explaining what I was looking for in my post, clearly I failed in that endeavour .

 

[Anseo]

Unless your present caravan 12V system was made before about 2000, it will already use a Switch Mode Power Supply (SMPS) which will produce at least 8A, or possibly 12A of smoothed 13.8V dc, and a few were even rated to 16A. These were in general capable of running the loads you have described without a 12V battery. The 12V battery was only necessary if the caravan was being used off grid.

However some caravans used inboard water pumps some of which had quite larger starting currents, and when they turned on the pulse of current they needed to get the pump turning cold cause momentary drops in the 12V wiring which could upset other appliances that were switched on. If that occured, fitting a 12V battery easily cured it.

I would suggest If you already have at least an 8A SMPS fitted as standard try using the caravan and see if you have any problems. If its OK then its saved you the cost and weight of a battery.

If on the other hand you seem to have any problems, then I suspect you might get away with 12ah gel battery, but certainly a 20Ah or bigger should do the trick.

Thank you Prof for taking the time to read and understand what I was trying to ascertain.

You have given me the answer I was hoping for, the additional information is both helpful and useful.

and appreciated.

 

[JTQ]

Is there not a risk with using too low a capacity batteries of over charging rates, should your battery ever need a significant recharge?
Previous held practice with LA Leisure type batteries was in Ah rating to size 10 times the charger max current, much higher charging currents leading to increased levels of battery damage. Technoloy changes so possibly old school practices are out dated, "smart" charging for example probably able to skirt round that issue.

 

[ProfJohnL]

Is there not a risk with using too low a capacity batteries of over charging rates, should your battery ever need a significant recharge?
Previous held practice with LA Leisure type batteries was in Ah rating to size 10 times the charger max current, much higher charging currents leading to increased levels of battery damage. Technoloy changes so possibly old school practices are out dated, "smart" charging for example probably able to skirt round that issue.

That is a good point, but assuming the caravan is only used on EHU pitches, the small battery will hardly be doing anything. The pulse of current needed to get the pump spinning lasts a fraction of a second, and it will barely take any charge from battery. You could almost get by with a large capacitor rather than a battery.

Every 12V 6 cell SLA battery(1.2Ah to 20Ah) I have seen has specified a constant charging voltage of between 13.2 to 13.8V ( some as much as 14.1V) which should maximise the life of the battery. The caravans SMPS should be fairly accurately set to 13.8V. Continuous operation at 13.8 should not damage the cells. These batteries are also normally rated for bulk phase charge voltages as high as 15V. The Charge rate is principally controlled by the cells in the battery and as the charger only gives 13.8V it should not exceed the maximum Coulombe rate.

 

[Beardy]

Reading above got me thinking. With no solar (at the moment) I've only stayed on sites with EHU, but I do have a motor mover. According to the manual the max current for my mover is 80 amps and average is 20 amps so *in theory* I could pick up a 40 ah car battery for £30 and still be able run the mover for 2 hours (I know that 2 hours would kill the battery and probably the mover as well). In reality I guess that I've actually used the mover for no more than 5 minutes at either end of my outings, As there is no alarm on my caravan I'm struggling to find a reason not to swap out the 100 ah leisure battery currently fitted and save 10-15 kg pay load.

 

[Anseo]

Reading above got me thinking. With no solar (at the moment) I've only stayed on sites with EHU, but I do have a motor mover. According to the manual the max current for my mover is 80 amps and average is 20 amps so *in theory* I could pick up a 40 ah car battery for £30 and still be able run the mover for 2 hours (I know that 2 hours would kill the battery and probably the mover as well). In reality I guess that I've actually used the mover for no more than 5 minutes at either end of my outings, As there is no alarm on my caravan I'm struggling to find a reason not to swap out the 100 ah leisure battery currently fitted and save 10-15 kg pay load.

Based on the specifications of this battery it would appear that there are sufficient Cold Cranking Amps to overcome the initial surge required to get the mover operating.

Bearing in mind that in order to preserve the longevity of the battery then only 20 amps is usable at maximum.
Taking your earlier calculations, that 20 amps represents approxiamtely 1 hour of usage, more than enough given your typical usage time(s).

And, assuming that you are providing a charge to the battery whilst towing should mean that you have a relatively healthy battery at your arrival point.

10 - 15 kilograms is a very significant weight saving, I like your thinking on this .

 

[JTQ]

I am not so confident that running a mover, for even 5 minutes is really that analogous to cold cranking an engine for what is at the most 10 seconds?
I suspect the battery could have to deal with those tasks quite differently, hence why we have "starter" and "traction" build technology batteries.

I for about a decade used a genuine Traction battery, a Varta to drive our mover. As I only used the mover at home, this was a portable unit left there on a smart charge 365 days a year. [The vans battery being a Gel technology type, was not suitable for powering a mover].
The point I am coming to is that was quite small, though the specific size I have now forgotten, certainly not more than 80Ah, probably 60Ah. The van weight was 1750kg, the duty quite difficult in being long and nothing but inclines, though down as well as up each way.
That did the job exceptionally well and for a very long time LA battery wise. However, here its recharging routine was extemporary, in being all but immediately back on charge, not brutally recharged but phased, plus it was never deployed other than being fully charged.
Quite a differing situation to many mover applications, however a very successful one.
Importantly in our case the mover "working" had, and has, a critical need. No way can I physically shift now 1900kg or even the old 1750kg van manually out of the lane on the inclines involved. If I could not move it then intervillage traffic around here can't get through.
I would not be over zealous in dropping to a very small battery, just settle for a modest weight saving, most certainly if buying what was built as a "starter" duty battery, not a "traction" build.

 

[Raywood]

I am not convinced the 10-15 kg saving you mention is worthwhile unless you feel you are very near to the MTPLM. when you look at the total weight of the outfit you will probably be looking at about 1% or even less of the gross weight and any saving on fuel will be negligible. We have certainly managed with a mover and 75AH battery so that should be a safe bet.

 

[ProfJohnL]

Reading above got me thinking. With no solar (at the moment) I've only stayed on sites with EHU, but I do have a motor mover. According to the manual the max current for my mover is 80 amps and average is 20 amps so *in theory* I could pick up a 40 ah car battery for £30 and still be able run the mover for 2 hours (I know that 2 hours would kill the battery and probably the mover as well). In reality I guess that I've actually used the mover for no more than 5 minutes at either end of my outings, As there is no alarm on my caravan I'm struggling to find a reason not to swap out the 100 ah leisure battery currently fitted and save 10-15 kg pay load.

Firstly as you have identified the information I have given was specifically without a caravan mover.

I have previously done a number of quick "in the margin" calculated estimates of how much battery capacity is typically used to position a caravan on site. If you could actually check how long the mover is actually moving the caravan it amounts to well under 5 min. and typically you will use less than 2Ah of battery capacity in the process.

It's generally the case the smaller the Ah rating of an LA or gel battery the smaller its peak or cranking amps will be.

You would need to choose a size of battery with a peak current delivery that equals or exceed the movers stated peak current.

 

[Beardy]

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Firstly as you have identified the information I have given was specifically without a caravan mover.

I have previously done a number of quick "in the margin" calculated estimates of how much battery capacity is typically used to position a caravan on site. If you could actually check how long the mover is actually moving the caravan it amounts to well under 5 min. and typically you will use less than 2Ah of battery capacity in the process.

It's generally the case the smaller the Ah rating of an LA or gel battery the smaller its peak or cranking amps will be.

You would need to choose a size of battery with a peak current delivery that equals or exceed the movers stated peak current.

You're probably right in that it's less than 5 minutes actual movement. I do tend to pause quite frequently to check what's going on around the caravan.

I don't think there is a problem with the peak current from a car battery, typically they are rated way in excess of 80 amps, the one @Anseo linked to is 330 amps CCA. The only thing I'm struggling to establish is whether drawing 20 amps for a few minutes would have a detrimental effect. The CCA quoted for car batteries seems to be based on 30 seconds. Is it fair to assume that a battery rated 320 amp CCA will be OK with 160 amps for a minute, 80 amps for 2 minutes, 40 amps for 4 minutes or 20 amps for 8 minutes? My gut feeling is that 320 amps for 30 seconds will be more harmful than 20 amps for 8 minutes but I can't find anything to back this up.

 

[ProfJohnL]

---

You're probably right in that it's less than 5 minutes actual movement. I do tend to pause quite frequently to check what's going on around the caravan.

I don't think there is a problem with the peak current from a car battery, typically they are rated way in excess of 80 amps, the one @Anseo linked to is 330 amps CCA. The only thing I'm struggling to establish is whether drawing 20 amps for a few minutes would have a detrimental effect. The CCA quoted for car batteries seems to be based on 30 seconds. Is it fair to assume that a battery rated 320 amp CCA will be OK with 160 amps for a minute, 80 amps for 2 minutes, 40 amps for 4 minutes or 20 amps for 8 minutes? My gut feeling is that 320 amps for 30 seconds will be more harmful than 20 amps for 8 minutes but I can't find anything to back this up.

I agree with your appraisal. The demands of a caravan mover I suspect are far less demanding than a car starter. Consequently a even a small car battery should be more than capable.

 

[trevormonty]

Is there not a risk with using too low a capacity batteries of over charging rates, should your battery ever need a significant recharge?
Previous held practice with LA Leisure type batteries was in Ah rating to size 10 times the charger max current, much higher charging currents leading to increased levels of battery damage. Technoloy changes so possibly old school practices are out dated, "smart" charging for example probably able to skirt round that issue.

AGM batteries do have max charging current see specs on batteries you are looking at using.
That is probably why my van states 60AH minimum. The easy way around this is to disable van charger and use one plugged into a power point. For 12- 20AH battery a 1-2amp charger will be ample as you aren't looking to charge battery regular from flat.

Between motor movers and ebikes carried in caravan my van is also mass limited. Solution going forward is 100AH 13kg LiFeP04 battery, fitted with Anderson connectors so I can easily remove it and place in car if need every last kg of weight saving. Currently have Anderson connectors on AGM battery but at 28kg will only remove it for big trips.