How many charges will I get from a 12 volt Lesiure Battery ?

[Rocker]

Thinking of buying a 12 Volt Leisure Battery to take down the field to charge my lipo batteries up .Before I invested in a 12 volt Battery I want to make sure it will be right for the job .The problem I might have is I only use 6c 5000 lipo .I am no good at working out things like this so would be grateful if one of you boffins could give me clue to how many 6s 50000 lipo I could charge up using a fully charge 12 volt Leisure before it ran out of go .Will I be able to get more then one 6s 5000 lipo charge up on this 12 volt battery ?

[Martin Harris - Moderator]

It will depend on the capacity of the leisure battery of course. Rough guess would be that you'll take something like 10Ah for each flight battery you recharge. Therefore if your battery is a 75Ah one, for example, you should get around 7 (and a half) charges from a fully charged leisure battery in good condition (10 from a 100Ah, 5 from a 50Ah etc.)

The easy way to visualise the working out is to think of the packs as 2 3S packs of around 12V each (nominal value of both the lead acid battery and the LiPo packs) and 5Ah (5000mAh).  Therefore 2 x 5Ah gives 10Ah.  In reality, the charger creates a suitable voltage in its circuitry (which will introduce some additional losses) to charge the 6S pack which will be around 25V but it's near enough for a ball park figure bearing in mind you (hopefully) won't be discharging your packs completely!

I'm assuming the 50000 pack mentioned in the OP is a typo!

Edited By Martin Harris on 24/02/2019 00:39:26

[Former Member]

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[Phil 9]

I may have this wrong but I was told you should only use about 50% of the leisure battery's capacity because if it discharges below that level it can be damaged

[Former Member]

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[Bruce Collinson]

Go for it Rocker, a long warm day’s flying is enhanced by the ability to recharge some of your LiPos and fly them again. I have an AGM leisure battery with a smart charger to keep it topped up and I believe these are the current vogue for this application.

i guess like most things in life, buying well at the outset is the order of the day so get a large capacity battery. They’re very heavy.

BTC

[Phil 9]

My personal preference was just to buy some extra lipo batteries for the model and charge one or two from my car battery at the field if I really needed too but a 6s 5000mah battery does take a good while to charge at the field.

One club I attended built a bank of leisure batteries into the club shed that were charged by a solar panel on the roof. it worked very well

a generator seems pintless to me as it generates noise and you still need to carry fuel with you. It would be simpler to  use an IC model as you just wiped out any advantages of electric power.

Edited By Phil 9 on 24/02/2019 08:49:53

[Rocker]

Thanks I take your point about the time it will take to charge a lipo up at the field Most of the people at my club take a 12 volt battery with them and charge up their lipo on anything from 5 amp up to 10 amps .I am not comfortable with that and only like to charge at 1 amp so considering how long it will take to charge a lipo at 1 amp I think I would be better using the money to buy some more lipo then

[Don Fry]

Or use, as one less than green member of this forum advocates, your car battery, with the car's engine running to recharge the battery.

But one point for longevity of a leasure battey is to keep it connected to a float charger between use sessions. They don't mind being run flat once in a while, but they object to storage at anything other than full charge.

Standard emergency services practice for the storage of there things, and I've seen 15 year old batteries still giving good service

[Engine Doctor]

If you go the battery route get the biggest capacity battery you can A afford ans B carry. AGM batteries are made to accept a charge quicker and used in Stop / Star car applications . The advantage is that they are less likely to leak any liquid unlike a normal car or leisure battery that can leak Sulphuric acid from the vent. The disadvantage is they cost considerably more .The number of charges you will get is also dependent on how many cells you batteries have , anything above 4 s will use considerably more current to charge it. The higher the cell count the more current.

As Phil 9 says its probably easier and no more expensive to take more batteries along. . The heli fliers at our club started using very large HV batteries in their models . They bought an generator and a decent charger/s along . Not a problem as it was tucked away in a hedge and a long lead supplied their charger/s

[Former Member]

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[Denis Watkins]

Posted by Rocker on 24/02/2019 08:58:32:

Thanks I take your point about the time it will take to charge a lipo up at the field Most of the people at my club take a 12 volt battery with them and charge up their lipo on anything from 5 amp up to 10 amps .I am not comfortable with that and only like to charge at 1 amp so considering how long it will take to charge a lipo at 1 amp I think I would be better using the money to buy some more lipo then

Percy spotted this Rocker,

The lads with a 5000ma lipo are charging between 5A and 10A

This is OK Rocker as they are charging between 1C to 2C, which takes half hour to an 1 hour

Me thinks too, Like Percy, you have taken onboard that 1C means 1A, which it could do with a 1000ma pack

[Phil 9]

one idea I had but never implemented was to wire a leisure battery into the car with a split charger

[PeterF]

I was faced with this conundrum some while ago flying an EDF model that has 2 x 8S 5000mAh packs, these are rather expensive to buy multiple sets. I also fly other larger electric models as well, but this is the highest capacity. Each recharge would take about 24Ah from a 12V battery, and a 100Ah leisure battery as someone has said should not be discharged below about 50%, I would get 2 charges. I was also not keen to go down the generator route, a small noisy open frame gennie would annoy the rest of the club members in the pits and a quiet suitcase Honda type would be expensive. Therefore, I have bought 6 low C rating 6S lipos of 16,000mAh capacity (16Ah) and put them into a parallel bank of 96Ah but nominally at 24V and it weighs less than a single lead acid leisure battery and give me 3 times the usable capacity. Admittedly, it cost 3 times as much as a single leisure battery, but Ah for Ah it cost no more and is a lot more convenient. Luckily my charger can be fed with up to 50V DC input so the supply voltage is not an issue.

I recognise that this is more of a specialist need, not suitable for everybody, but thought it worth mentioning as another way of solving the problem.

[Phil 9]

well there is no one size fits all solution as peters example demonstrates

[Dickw]

I have tried many Leisure batteries over the years and don’t think they are suitable for our application – none that I bought delivered on capacity or lasted more than 2 years at best. The car batteries I tried actually worked better.

About 6 years ago I invested in a 12v pack made up of 8 x 15Ah Life cells (marketed for electric bikes) in a 4s2p configuration. Although only a nominal 30Ah, the Life cells have a flatter voltage curve under load and handle deeper discharge better so it gives me far more charges than any 75Ah Leisure battery ever did. Also it weighs a lot less, and is still going strong after 6 years.

Why do I field charge?

Yesterday I had 8 flights, and the batteries I use cost more than £50 each. I took 4 charged batteries with me and recharged each on site. To have eight batteries would mean spending another £200 just for one type of aircraft.

Because of weight and space considerations I use a small 2s 300mAh Rx battery – I also recharge those between flights just to be on the safe side.

Dick

[Steve Hargreaves - Moderator]

The best way to work it out is to use the concept of "Watt-Hours" as a representation of the energy stored in the battery.....

To make the maths easy lets consider a 100Ah Leisure battery this contains 12V x 100Ah equals 1200Wh of energy.....so if we take Rockers 6S 5000mAh (or 5Ah) battery that's 22.2V x 5Ah equals 111Wh of energy.....

1200 divided by 111 equals 10.81 charges....simples....

Now come the caveats.....first one...no charging is 100% efficient so you'll lose some energy there....lets say the process is about 80% efficient....second one...the Lipo won't be completely flat when you come to charge it....most people aim for about 20% capacity left at the end of a flight (so this kind of cancels out the loss of efficiency).... third one.... as others have said lead acid batteries really do not like being fully discharged.....Deep cycle batteries (which leisure batteries are supposed to be) can stand it better than say ordinary car batteries. Fourth one...they are flippin heavy...a 100Ah battery will be something like 20kgs plus....is the field far from your car?

A good source of Leisure batteries is here.... no link other than being a satisfied customer.... Check out their range of Lithium leisure batteries too.....100Ah...£1,000....bargain...

Hope that helps....

[Former Member]

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[Steve Hargreaves - Moderator]

Posted by Rocker on 24/02/2019 08:58:32:

Thanks I take your point about the time it will take to charge a lipo up at the field Most of the people at my club take a 12 volt battery with them and charge up their lipo on anything from 5 amp up to 10 amps .I am not comfortable with that and only like to charge at 1 amp so considering how long it will take to charge a lipo at 1 amp I think I would be better using the money to buy some more lipo then

Charging a 5000mAh LiPo at 5A is only 1C...10A would be 2C & most Lipos will take this easily. At 5A your LiPo will be charged in about 1 hour.....at 10A about 30 minutes. Charging at 1A is only 0.2C & would take approximately 5 hours to fully charge your LiPo Rocker by which time it will be dark....

[Former Member]

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[Phil 9]

Posted by Dickw on 24/02/2019 10:30:24:

I have tried many Leisure batteries over the years and don’t think they are suitable for our application – none that I bought delivered on capacity or lasted more than 2 years at best. The car batteries I tried actually worked better.

About 6 years ago I invested in a 12v pack made up of 8 x 15Ah Life cells (marketed for electric bikes) in a 4s2p configuration. Although only a nominal 30Ah, the Life cells have a flatter voltage curve under load and handle deeper discharge better so it gives me far more charges than any 75Ah Leisure battery ever did. Also it weighs a lot less, and is still going strong after 6 years.

Why do I field charge?

Yesterday I had 8 flights, and the batteries I use cost more than £50 each. I took 4 charged batteries with me and recharged each on site. To have eight batteries would mean spending another £200 just for one type of aircraft.

Because of weight and space considerations I use a small 2s 300mAh Rx battery – I also recharge those between flights just to be on the safe side.

Dick

I built my own 12v pack from 18650 cells I bought used from ebay that I use for camping. As they were used they did not have full capacity but I discarded any with less than 1Ah capacity mine has 48 cells arranged as 3s so has a 16Ah capacity. Lot of youtube videos showing people build larger packs to power cars or even homes link . it was more of a fun project as it can be time consuming to test the cells and assemble but if you have the patents it may provide an alternative route

Edited By Phil 9 on 24/02/2019 13:38:23

[Dickw]

These are the LifeP04 cells I used - expensive initially but have worked out a lot cheaper in the long run.

They fit in the bottom of my model box and still leave room for chargers, heated battery storage, and tools.

Dick

[Martin Harris - Moderator]

Posted by Dickw on 24/02/2019 10:30:24:

I have tried many Leisure batteries over the years and don’t think they are suitable for our application – none that I bought delivered on capacity or lasted more than 2 years at best. The car batteries I tried actually worked better.

Dick

Interesting observation...many years ago, I lived at a gliding club for a couple of years in a caravan. I fitted a second battery to my car with a split discharge system (a 30A relay) and used it to power the lights and TV. This was a normal cheap to mid-range car battery and I habitually discharged it through the long winter evenings until the TV screen shrunk and the lights went dim. After a 30 mile round trip to work and back, I would repeat the cycle the next night.

That battery saw me through two winters and was still going strong when I rejoined the ranks of bricks and mortar dwellers.

I have to say that although my club provides a solar powered battery system (twin 110Ah UPS batteries) which seems to cope with quite high demands rather admirably, my preference for larger energy requirements is to cut out the middle man and bring it in liquid form...