Typical current draw for 12 volt systems to aid planning of battery needs and future trips without EHU? (1 Viewer)

[68c]

Why the negative lead?
Not that important to be fair, providing only one lead to the battery use pos or neg. I just said neg as I have seen vans with several input/outputs to the battery pos terminal but usually only one to the neg. Especialy if there us a battery monitor fitted.

 

[nicholsong]

I think that I have not seen mention of B2B to enhance off-EHU ability.

We have 2 X 90Ah LA batteries and 80W solar.

With that set-up and B2B we never have to think of needing more. The B2B seems to top-up the batteries to full charge aftter 2 nights static with about a 40 min drive.

 

[autorouter]

Is there a simple way to understand leisure batteries. For example if you have a 100 ah battery would that equate to 100 hours at 1amp use, 20 hours at 5 amp use, 10 hours at 10 amp use? Does a 130ah give you 30 more hours at 1amp use than a 100ah? In short does the bigger ah battery give you more power or a longer period?

Yes that's more or less how it works. If you look at the battery spec you will probably see that the '100Ah' is for the '20 hour rate' (C20), so it will give 5 amps for 20 hours. Lower amps will last a bit longer than you might expect, so for 1 amp it might last 110 hours, not 100 hours. However higher amps will last a shorter time than expected, so 20 amps might last 4.5 hours, not 5 hours.

A 130Ah will behave as if it has 30% more capacity than a 100Ah, so a bigger battery will give you more amps for the same time, or more time for the same amps. The Ah capacity is a fixed amount of charge, you can choose to take it out slowly over a long time, or quickly over shorter time.

But as others have already said, you can't use all of the charge completely without damaging the battery. So flooded lead-acids should only be taken down to the 50% level for the battery to have a reasonable lifetime. Gels and AGMs can usually be taken down to the 20% level, so you get more usable charge from a 100Ah gel than a 100Ah flooded. A lithium battery can be taken even lower, to 10% or even to zero.

 

[meanders]

Doing the trip the OP proposes, I foresee no problems if you are not watching hours of TV. If using Aires you will be coming every couple of days and that will top up the battery in no time. We have done similar many times in three vans. The first had single LA battery, the current one has two. The first van had no solar and we went weeks away and never had a problem.

Sensible precautions like not leaving the awning light on. We never watched TV when abroad and rarely at home. An odd DVD when we had kids with us the weather was bad. Radio is a portable with rechargeable batteries.

We always charge devices when driving except a single phone overnight using 12v > usb charger. I fretted about this in 2003 but soon realised that cautious use meant I could relax. Like most I would check the battery state on the panel each morning.

We don't carry coffee machine, electric kettle, toaster or anything else like that. Everything runs off gas.

Let's face it, at worst case, you start the engine for a relatively short while.

 

[PlacidoD]

"But as others have already said, you can't use all of the charge completely without damaging the battery. So flooded lead-acids should only be taken down to the 50% level for the battery to have a reasonable lifetime. Gels and AGMs can usually be taken down to the 20% level, so you get more usable charge from a 100Ah gel than a 100Ah flooded. A lithium battery can be taken even lower, to 10% or even to zero."

To add to the above you cannot assume an ability to do a straight swap to gels or AGMs. The battery chargers for them has a different charging profile. You will damage the battery if your charger is flooded lead-acid only. (The same applies to lithium but I think most of us know that). A new charger will cost maybe £80 or more if you go for bells and whistles and you have the pfaff of fitting it (and in my case finding it before even considering replacing it!!!)

Chris

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[Dave and Jan]

Yes that's more or less how it works. If you look at the battery spec you will probably see that the '100Ah' is for the '20 hour rate' (C20), so it will give 5 amps for 20 hours. Lower amps will last a bit longer than you might expect, so for 1 amp it might last 110 hours, not 100 hours. However higher amps will last a shorter time than expected, so 20 amps might last 4.5 hours, not 5 hours.

A 130Ah will behave as if it has 30% more capacity than a 100Ah, so a bigger battery will give you more amps for the same time, or more time for the same amps. The Ah capacity is a fixed amount of charge, you can choose to take it out slowly over a long time, or quickly over shorter time.

But as others have already said, you can't use all of the charge completely without damaging the battery. So flooded lead-acids should only be taken down to the 50% level for the battery to have a reasonable lifetime. Gels and AGMs can usually be taken down to the 20% level, so you get more usable charge from a 100Ah gel than a 100Ah flooded. A lithium battery can be taken even lower, to 10% or even to zero.

Thanks for that. When I looked We have an AGM battery. I said in a previous post it generally drops to 12.1-12.3v overnight and was informed that is more than 50% but I think it was assuming it was LA. If they can drop to 20% is that in their range, ie does it still sound healthy? After reading replies I did order a new 120ah AGM battery online last night despite the fact we’ve never had a problem.

 

[PlacidoD]

Is there a simple way to understand leisure batteries. For example if you have a 100 ah battery would that equate to 100 hours at 1amp use, 20 hours at 5 amp use, 10 hours at 10 amp use? Does a 130ah give you 30 more hours at 1amp use than a 100ah? In short does the bigger ah battery give you more power or a longer period?

Others have already answered this. I would add two observations:
1. If your leisure battery is in good condition and you are in an older van the most economical improvement you can make is to replace halogen bulbs with leds. I replaced 12 bulbs over the weekend reducing the consumption from 10 watts to circa 2 watts whilst doubling the light output. So 20 watts with them all on rather than 120 watts.
2. With most vans your 12 volt power still comes from the battery even though you are on an EHU. So the rate at which your charger recharges has some relevance. I had fondly assumed that there would be a transformer stepping down the 240 volts to run the 12 volt system. Not so on most vans. So you will be well below 100% if you light up like Blackpool illuminations and run the heating overnight and the recharging will take time. I discovered the weakness of my leisure battery while on an EHU not realising that. (That proved a blessing in disguise given, as set out in this thread , plans to be without an EHU on a few nights. New battery now in place and I am musing on fitting a 2nd.)

Chris

 

[Dave and Jan]

Others have already answered this. I would add two observations:
1. If your leisure battery is in good condition and you are in an older van the most economical improvement you can make is to replace halogen bulbs with leds. I replaced 12 bulbs over the weekend reducing the consumption from 10 watts to circa 2 watts whilst doubling the light output. So 20 watts with them all on rather than 120 watts.
2. With most vans your 12 volt power still comes from the battery even though you are on an EHU. So the rate at which your charger recharges has some relevance. I had fondly assumed that there would be a transformer stepping down the 240 volts to run the 12 volt system. Not so on most vans. So you will be well below 100% if you light up like Blackpool illuminations and run the heating overnight and the recharging will take time. I discovered the weakness of my leisure battery while on an EHU not realising that. (That proved a blessing in disguise given, as set out in this thread , plans to be without an EHU on a few nights. New battery now in place and I am musing on fitting a 2nd.)

It’s a newish van, 2020. Everything is LCD. It came with a Banner 100ah AGM battery hence now 4 years old. We do a lot of non EHU camping. Usual stuff, fridge, lights, some tv at night, phones in charge, water heater, heating if cold etc. Generally move on the next day. Have solar and can go to battery levels in the control panel where you can see both battery voltages, actual amp draw and solar or EHU charge rate. Following the thread yesterday looking at the panel both batteries reading 12.8v, with the lights on leisure dropped to 12.6, lights using 2amp solar was putting in 1.5amp. Turned lights off battery went straight back to 12.8v. Does that sound healthy but I have ordered a new 120ah AGM online as I’m no longer confident.

 

[Lenny HB]

Thanks for that. I have a 100ah LA battery. It’s 4 year old but just been tested good this week as part of the Hab check

They will have done a CCA test which is totally meaningless on a leisure battery.
Only way to test a leisure battery is with a slow discharge test which rakes a long time.

 

[meanders]

Not sure if it's entirely meaningless. It definitely picks up batteries are on the way out. I agree that a clean bill of health may not be correct though.

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[Lenny HB]

Not sure if it's entirely meaningless. It definitely picks up batteries are on the way out. I agree that a clean bill of health may not be correct though.

From experance they will often pass a battery with a reading of 80 % but on a low current draw of 5 to 10 amps it's only good for 10 ah. I had two like that, wouldn't change them under warranty because they passed a CCA test.

 

[PlacidoD]

"... Have solar and can go to battery levels in the control panel where you can see both battery voltages, actual amp draw and solar or EHU charge rate. ..."

That sounds very useful!! The control Panel on my Hobby is more basic and far too small for easy reading. I do have a separate solar read out hidden away in a locker but have no idea atm on EHU charge rate. When I find the damn thing (Presumably under the passenger seat behind the fuse box) I can check but that sort of thing ideally sounds like a job for when the van is on SORN on the drive in deepest winter!

Chris

 

[autorouter]

Following the thread yesterday looking at the panel both batteries reading 12.8v, with the lights on leisure dropped to 12.6, lights using 2amp solar was putting in 1.5amp. Turned lights off battery went straight back to 12.8v. Does that sound healthy

Sounds fine to me. Remember that the only voltage that in any way indicates the state of charge is the 'resting voltage'. That's the voltage with no charging and no load.

When you switched on the lights, the voltage at the terminals drops a bit due to the battery internal resistance. when you switch them off, the voltage goes up again. So the sudden drop in terminal voltage does not represent an immediate loss of charge.

 

[Dave and Jan]

One last question. If the battery is 100ah and you can only take it down to say 20% for an AGM battery or 50% for Lead Acid, does that mean you only have 80ah to use on an AGM and 50 on a lead acid?

 

[1967bowesj]

One last question. If the battery is 100ah and you can only take it down to say 20% for an AGM battery or 50% for Lead Acid, does that mean you only have 80ah to use on an AGM and 50 on a lead acid?

Yes the rest is like a safety net before you get damage

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[Richard n Ann]

One last question. If the battery is 100ah and you can only take it down to say 20% for an AGM battery or 50% for Lead Acid, does that mean you only have 80ah to use on an AGM and 50 on a lead acid?

Yes exactly

 

[Lenny HB]

Yes but I wouldn't take an AGM down to 20% best to stick to 50%, Gels are OK down to 20%.

 

[Dave and Jan]

Found this so would appear my AGM battery was probably still ok discharging to between 12.1-12.3v overnight in use. New 120ah AGM being delivered today so I’ll change it anyway.

 

[Lenny HB]

Found this so would appear my AGM battery was probably still ok discharging to between 12.1-12.3v overnight in use. New 120ah AGM being delivered today so I’ll change it anyway.



View attachment 921068

Those voltages are very low, I2.6v is normally 75% charged.

 

[Steve I]

Very interesting and I have another related question if anyone can help please. My van has a Webasto 50 diesel heating system and I wondered if anyone had any numbers for the draw on that? It kicks the leisure battery hard on start up but then settles although it definitely uses battery for the fan to circulate and found out my first leisure battery last year which wouldn’t fire up without engine running. Only got 100W solar but the replacement of 105ah LA with a 160ah carbon gel battery has been good for the last 12 months off-grid for 2-3 days, although looking for longer potentially with long break away in the Autumn and more off-grid

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