Trouble with watts & amps etc - Advice please

g4fne

Novice Member
Hi folks.

I could really do with some advice in regards to portable power & charging options etc.

I enjoy a bit of camping & can be away 2or3 weeks at a time. I am trying to avoid electric hook ups as it can be restrictive. The only things i need power for is my Archos media player (which needs 6V 2amp) & a couple small lights in the tent.

So my latest idea is to buy a couple of 20ah sealed lead acid battery & rotate them over the duration of being away. These are a lot lighter & less bulky than the other options (leisure battery or powerpacks etc) & hopefully more versatile.

The problem i have is charging. When driving I need to be able to charge from my cigarette lighter of the car. I need a charger that will output as near to 10amp as possible without going over so the 20ah battery charging process takes approx 2-4 hours (i assume this is correct??)

The charger i'm looking at is the ring RSC16 smart charger Smart Charger - Portable Power > Smart Chargers > Smart Chargers Unfortunately this does not come with a cigarette lighter adaptor, so as i understand it, i will need an inverter.

The inverter i'm looking at is the Belkin Anywhere Power Inverter Belkin Anywhere Power Inverter 140W F5C412UK140W - PC World Business Online Store UK - Buy The Best Deals Online. This comes in two power sizes. Smaller provides 140w & bigger one provides 300w.

According to car handbook, my cigarette lighter is limited to 10amp output so i'm assuming anymore than that will either blow the cigarette lighter or the car fuse.

Can anyone tell me what 140w or 300w relates to in terms of Amp per hour ?? .... I'de like to get to as near as 10amp as possible without going over as i assume a 20ah batter should charge between 2&3 hours with the ring smart charger.

Can anyone also tell me if my plan is completely flawed & i'm missing something ??
 

clockworks

Novice Member
You're going to convert the 12v from the cigarette lighter to 240v with an inverter, then convert the 240v back to 12v with the charger? It'll work, but it's not efficient - each time you convert the voltage, you'll lose 25-50% of the power as heat.

For charging a lead acid battery from a car cigarette lighter, an RC battery charger like this: GT Power V5 balance Charger Li-po NI-MH Battery will be more efficient.

Then you need to think about what voltage you need to run your devices. If you use a 12v battery, you'll need to use an inverter and the original AC adaptor for your Archos. Again, you'll be wasting power and losing runtime.
What voltage are your portable lights?

If you were to use a 6v battery, and 6v lights, you could run everything in the tent direct from the battery, so your battery would last longer.
Maybe consider getting 6v LED lights as well, as they are more efficient than filament lamps.
 

g4fne

Novice Member
Thanks for the response. It'll take me a bit of time to get my head round as i'm finding the sbject a little baffling.

I kinda understand there is an element of ineffeciency of the charging set up, due to the inverter, but my Archos (3-4hours a day) & flourescant lamp (little use, only short periods or in emergency) already have cigarette lighter connectors that i was planning to use that straight off the 20ah battery in the tent (will obviously need to get a female cigaretter lighter for battery end).

Does this mean that these will still be running inefficiently ??
 

nheather

Distinguished Member
If your archos and lamp will run off 12V I don't understand why you need the inverter.

Just charge the battery up from the car and then power your kit off the battery.

A 20Ah battery will deliver 20A for 1 hour. It's a linear relationship so if you only draw 5A then it will last for 4 hours.

Assuming your Archos really does draw 2A (I doubt it as that is a large current for a portable device) then it would run for 10 hours off the battery.

In reality I suspect it will run for a lot more. I reckon the 2A is the current it uses to fast charge the Archos internal battery, not how much the Archos needs to run.

Which Archos is it - I will try and look up it's true current draw.

Cheers,

Nigel
 
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g4fne

Novice Member
Charging the battery direct from the car cigarette lighter would be an ideal scenario, but the only charger that i can find that outputs anywhere near 10amps this way is the CTEK Multi XS 7000 Battery Charger and Conditioner (outout 7amp) & at £110 (including cigarette lighter adaptor) is a bit steep, though the simplicity of this option is starting to appeal :):). If anyone knows of a cheaper alternative i'de be greatful for the pointer.

I've got an Archos AV700TV .... The 6V 2amp info did indeed come from the charging plug & was the only info i can find on power consumption. It would be very useful to know what the actual consumption is
 
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nheather

Distinguished Member
From what I can see, the internal battery is 5.75Ah and will give

16 hours music, 4 hours video or 3.5 hours digital TV.

Taking worst case, 3.5 hours this would equate to 1.6A (higher than I expected).

So from the 20Ah battery you would get 12.5 hours worst case.

Cheers,

Nigel
 

clockworks

Novice Member
I agree with Nigel - if you've already got 12v adaptors for the Archos and the lights, you don't need the inverter. A 12v battery will do the job.

That charger I linked to will charge a 12v battery at up to 5A, and only costs £30. You can even use it to charge the battery when the car is parked - if the car's battery drops too low, it'll switch off before the battery goes flat.
 

nheather

Distinguished Member
One thing to check with that charger though - it is designed for LiPo and NiMh and I suspect that the OP's battery is Lead Acid, which requires a different charging method (constant voltage rather than constant current).

If I am right, also be careful about using a car charger to charge this battery. These portable batteries have the acid in the form of a gel whereas in a car battery it is liquid. The liquid design can take a lot more abuse than a gel one and as such car chargers can get away with being quite primative.

With Lead Acid, you can't fix the current. You fix the voltage and the battery will draw the greater of

What it can take based on its internal resitance and the current cell volatge
What the supply can deliver

So in short the charger can current limit but it can't fix the current being delivered. In fact as the charging progresses the current will fall as the battery voltage gets closer to the charger voltage. It's like having a built-in cut-off.

You could charge directly off the lighter socket, perhaps with a current limiting resistor in series.

Cheers,

Nigel
 

clockworks

Novice Member
These RC chargers (there are loads of different models that use the same electronics) have lead acid programs as well as LiPo and NiMH. They are designed to charge the lead acid gel cells used by nitro fliers in their flight boxes.

I've got 2 similar chargers. The lead acid program can select the number of cells (2 to 6) and the current (0.1A to 5A).
Should work fine for the OP's batteries.
 

nheather

Distinguished Member
Sorry my mistake - I just read the spec and it only talks about LiPo and NiMh but I see on the actual panel of the charger that it does do Lead Acid aswell.

Might get one myself - at the moment for my planes I have

A Nicad\NiMh charger
A LiPo Charger
A LiPo balancer
A lead acid charger

Cheers,

Nigel
 

g4fne

Novice Member
These RC chargers (there are loads of different models that use the same electronics) have lead acid programs as well as LiPo and NiMH. They are designed to charge the lead acid gel cells used by nitro fliers in their flight boxes.

I've got 2 similar chargers. The lead acid program can select the number of cells (2 to 6) and the current (0.1A to 5A).
Should work fine for the OP's batteries.
Can this kind of charger be powered from a car cigarette lighter, will it have an otput of 5amp via cigarette lighter connection (therefore charge a 20ah in approx 4hours) ??



To be clear to folk. I only required an inverter to allow connection of the charger i had my eye on (as it didnt have a cigarette lighter connection). I was not looking to power the Archos or lights via inverter as they would be connected directly to the 20ah lead acid battery. I'm not sure if i'm explaining myself very well .... it also doenst help being a novice at this sort of thing so i appreciate peoples patience & for posting responses :):)
 

nheather

Distinguished Member
Yes they can, but for most (including the one linked) you will need an adaptor as the charger just has croc clips which you would normally connect to a lead acid battery.

You would need to get a cigarette lighter plug with either flying leads to clip the crocs to (take care not to short) or safer, use it to replace the croc clips.

Another thing to consider is that the power leads on these chargers may be quite short which might be inconvenient if you are charging whilst driving.

Cheers,

Nigel
 

g4fne

Novice Member
or invest in camping electrics which plug into the bollards, and have three plugs on the other side as well an rcd.

Then you'll be able to charge your archos.

Thanks .... have done the electric hook up in the past but prefer to be independant if i can
 

clockworks

Novice Member
I've just checked my charger (it's actually the exact one that I linked to) and the input leads are 18" long. Easy enough to extend the leads, or make an adaptor, if you know someone with a soldering iron.

It's rated at 50 watts, so it'll do 4-and-a-bit amps in real life, taking about 5 hours to fully charge a 20AH battery from flat.

You might find it easier to use the charger as intended - straight off the main car battery - while the car is parked. Most cars these days have switched cigarette lighter sockets - they only work with the key in the ACC or RUN positions.

Nigel:
These chargers, and the many other types that use the same electronics from other Chinese "makers", are excellent value for money. Many of the racers and fliers that I know use them - not a single breakdown yet.
 
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g4fne

Novice Member
I'm now starting to grasp this a bit more. Would the car battery cope with charging 20ah battery for 5hours without itself going flat ??
 

clockworks

Novice Member
Most car batteries are at least 40AH, so, as long as the battery is in good nick, it'll be fine.
 

g4fne

Novice Member
I hate to do this as you guys have been very helpful, but to simplify things further, does that mean i could actually power my Archos (2amp approx) for 3-4 hours a day direct from cigarette lighter of the car with little affect on the car battery. The car is only 6months old Volvo V70 diesel so would think it would be about a 70ah battery ???? .... I have been nervous of this option because of possible problems if i flatten the car battery
 

nheather

Distinguished Member
From my previous post, 4 hours at 1.6A (worst case current draw) is 6.4Ah or 9.1% of your battery capacity.

So if you were to do it with the engine stopped then you would use 9.1% of the battery capacity - not a problem.

If you were to do the same with the engine running then the alternator would be able to cope so wouldn't drain the battery at all.

Cheers,

Nigel
 

nheather

Distinguished Member
These chargers, and the many other types that use the same electronics from other Chinese "makers", are excellent value for money. Many of the racers and fliers that I know use them - not a single breakdown yet.
Yeah, I've got my collection because of how my hobby has evolved.

When I first started, just needed to charge my Rx and Tx batteries and my lead acid starter battery.

Then I got a hummingbird so needed a simple LiPo charger.

Then I got a TRex with bigger LiPos and all the scare about balancing so I got the balancer.

But perhaps I should get a one size fits all solution.

Cheers,

Nigel
 

IronGiant

Moderator
thanks again Nigel. The engine would be off so it would use approx 10% of the battery
Each nights use would use 10% of the battery, so you'd probably want to be sure you were using the car for a couple of hours at least every other day to keep the car battery fully charged up. A better option may be to get a leisure battery and make sure it is fully charged before you go away, this will give you several days use without risking the car battery at all. Then every time you go for a drive plug the leisure battery straight into the cigarette lighter to top it up. Then you never put the car battery at risk, the worst case scenario is that one night the light in the tent will go out. Which is much more preferable to finding that the car won't start one morning.

If you go for one of the emergency starter/powerstation options then it will come a mains charger, a 12V connection to run from the car cigarette lighter to charge on the move and have a cigarette socket on it to run your equipment. You can also plug a solar panel into it to help keep it topped up during the day...

eg: this one which comes with 260psi air compressor, USB power socket, 2 x 12V power outlets, battery level gauge, LED work light, heavy duty booster cables with insulated clamps AC and DC chargers included. And a built in light duty inverter.

Buy 6-in-1 Heavy Duty Portable Power Station and Jump Starter. at Argos.co.uk

You can get cheaper ones with less gadgets, but you get the idea. I keep a simple one in the boot permanently connected to one of these on the rear parcel shelf:
12v Solar Panel Battery Trickle Charger caravan car on eBay (end time 10-Feb-10 09:31:29 GMT) it was invaluable when my car battery packed up in the snow.

Dave
 

g4fne

Novice Member
Each nights use would use 10% of the battery, so you'd probably want to be sure you were using the car for a couple of hours at least every other day to keep the car battery fully charged up. A better option may be to get a leisure battery and make sure it is fully charged before you go away, this will give you several days use without risking the car battery at all. Then every time you go for a drive plug the leisure battery straight into the cigarette lighter to top it up. Then you never put the car battery at risk, the worst case scenario is that one night the light in the tent will go out. Which is much more preferable to finding that the car won't start one morning.

If you go for one of the emergency starter/powerstation options then it will come a mains charger, a 12V connection to run from the car cigarette lighter to charge on the move and have a cigarette socket on it to run your equipment. You can also plug a solar panel into it to help keep it topped up during the day...

eg: this one which comes with 260psi air compressor, USB power socket, 2 x 12V power outlets, battery level gauge, LED work light, heavy duty booster cables with insulated clamps AC and DC chargers included. And a built in light duty inverter.

Buy 6-in-1 Heavy Duty Portable Power Station and Jump Starter. at Argos.co.uk

You can get cheaper ones with less gadgets, but you get the idea. I keep a simple one in the boot permanently connected to one of these on the rear parcel shelf:
12v Solar Panel Battery Trickle Charger caravan car on eBay (end time 10-Feb-10 09:31:29 GMT) it was invaluable when my car battery packed up in the snow.

Dave

Excuse my ignorance, but are you saying that by connecting a leisure battery direct to my cigarette lighter ... ie crocodile clips on battery to cigarette lighter input in car, that this will charge the leisure battery directly (when on the move) therefore a charger would not be required ??
 

nheather

Distinguished Member
IronGiant is right about consecutive charges without driving the car.

However, you need to look carefully at the sort of thing linked in Argos. Could be fine but two things you need to check

(i) What is the capacity of the internal battery

(ii) How fast does it charge when plugged into the lighter socket

If it is intended for short emergencies the capacity may be quite a bit smaller than your current one. Also the charge may be based on a trickle charge (one of the reviews talked about charging it for the recommended 27hrs before first use).

Also remember that with a full charge of your 20Ah battery you get 3 days use at 4 hours per day. If you are using the car in the meantime then you could be charging it.

Sorry, in answer to your question, the power system linked does not need a seperate charger - just plug into a lighter socket or use the mains charger at home.

And the solar panel listed would require 160 hours to charge the 20Ah battery.

Cheers,

Nigel
 
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g4fne

Novice Member
I do already have a power pack thats 13ah inbuilt battery but it does take an age to charge back up again & to be honest quite bulky for the amount of power ... if i was considering something this sort of size then a 85ah leisure battery or couple 20ah lead acids would seem the obvious route (back to original plan !!)
I'm discarding using the car battery (again) .... its not worth the risk i dont think.

I am very intrigued to hear how a leisure battery can be charged direct from the car cigarette lighter ..... as i move once or twice a week it would get a 3-4 hour car journey to charge back up which appeals, but surely it would need some sort of charger between the battery & the car cigarette lighter .... or have i misunderstood ???
 
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