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Old Apr 19, 2009, 04:28 AM
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Brisbane, QLD, Australia
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Question - Zip charging - getting my head around using a dedicated battery for this..

Hi,

Just a question about Zip Charging - I have already built a Dan's Charge Cut-off circuit, and plan to put about 2000mA back into the 3s batteries.

If I get an 18Ah 12V SLA battery, how many times can I charge the 3s packs before I get to a safe low voltage with the SLA that I have to stop?

A guess would be 8 - because I take the 18/2 which gives 9, and leave another 2A as a safety buffer for the SLA.

Am I thinking this out right? OR would I get more? Or less?

I've heard of people using their car batteries, I've only got a small car and worried that I will charge till I can't start. (but maybe with a few A123 packs I could start the car LOL)

I'm probably going to build a 12v safety cutout circuit if I use a large SLA battery and can get a decent amount of charges out of it. That way I can run the battery down to a pre-set limit. But is it worth investing in an 18A 12V SLA battery to take to the field or will this only give me less than 10 charges?
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Old Apr 19, 2009, 07:23 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Each 2300 mAh A123 cell requires approx.0.66Ah to recharge , 3X.66=1.98 Ah ,might asw well call it 2Ah.

A 17Ah Pb is going to drop like a brick under normal Zip charge charging rates, but if you charge slowerand are patient you can use perhaps 6 Ah from that baytter which would be 3 charges.

Have you read my $10 charger ( Zip Charging) Thread?


Charles
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Old Apr 23, 2009, 07:46 AM
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I've seen the setup on the back of the vehicle I am seriously contemplating a second car battery or something as it takes me just over 1 1/4 hours to get to the flying field, and I want to be able to have more flight time than driving time... I am really tempted this weekend to get a few zip charges out of the standard car battery - it is only rated at 300cca though - not sure what it equates to in real Ah capacity.

Also thinking more about it - with a long drive to and from the air field, maybe I *could* get away with just using the standard car battery but how many charges can I safely get away with before being stranded?

What about if I cart the lawnmower battery pack (24v 10A) with me to the field - I can use the Zip charge method - would there be any difference in using it as a 12v 10A SLA seperately as to just feeding the 24v into the zip charger?

At present I am getting back into the swing of the heli (literally!) and am planning this more carefully.
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Old Apr 23, 2009, 02:02 PM
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Joined Aug 2004
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I have a 24AH 12V jump starter SLA battery and I wouldn't even think of using it for zip charging. I only use it with my chargers to draw 2A~4A for small lipo packs.

I'd also strongly recommend *not* using a conventional car starting battery for zip charging, as it is not designed to withstand the current demand. You will find that in addition to possibly not being able to start your car, the car battery will quickly begin to lose capacity and you will need to replace it in short order (I speak from experience).

For zip charging, purchase the largest deep cycle battery you can afford (and can carry!), and a good 12V charger.

Ron
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Old Apr 24, 2009, 04:59 AM
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So a battery like this would be good?

http://www.jaycar.com.au/productView...T&SUBCATID=250
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Old Apr 24, 2009, 05:33 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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I use to use a 50AH battery which cost approx. $130 5 years ago.

http://www.rcgroups.com/forums/showt...7&highlight=50


I went to the dual 125 AH flooded cell deep cycles as they provide 5 times the capacity for the same cost.

When it comes to batteries as a power source for field charging then way to big is really barely big enough.


http://www.rcgroups.com/forums/showp...24&postcount=4


Charles
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Old Apr 24, 2009, 06:42 AM
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Brisbane, QLD, Australia
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Also considering replacing the car battery with something like an Optima Yellow - that way I can have a good battery that (from what I have read) should be able to replace my normal car battery when that gives up the ghost, as well as being able to use it separately for Zip charging.

Or I might just be able to pop this in the car (the Optima Yellow) so it gets charged all the time and can zip charge from it on a weekend and recharge by the time I drive home Maybe?
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Old Apr 24, 2009, 07:08 AM
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Actually this is looking more and more attractive: it's not terribly heavy and I think from the reading tonight I can use/obtain a good 12v charger, and this would last me a fair while and a lot of charges of 3SA123's right?
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Old Apr 24, 2009, 07:34 AM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Please use the linkes I have provided.

In extremely simple terms. Any sealed battery will cost approx. 3 to 6 times as much as a flooded cell battery of the same cpacity.

There are really only three reasons to use a sealed Pb battery instead of a flloded cells one.
1: It has to be in a location that if turned over would create a major problem.
2: You like to brag about how much you paid for it.
3: You have lots and lots of money and price is no object,see reason #2. If this is the case purchase the largest Lifeline sealed Pb you can justify / carry.

Once again each A123 cell will require approx. .66Ah to recharge, a 3S will required approx. 2Ah. based on my experience a 50Ah deep cycle is really closer to 30 AH at a high rate of discharege. You should not discharge it more than 50% so you could get approx. 7 3S chaeges from a 50AH. The last 3 or 4 chareges will be slowere however due to voltage drop under load.

Best compromise if you want to use same battery for auto and field power source is to either use a Marine Hybrid (combination stsrting / deep cycle) or a true deep cycle approx. 40% more AH than your standard starting battery. True deep cycles do not have as many CA / CCA as regular starting batteries.

Simple fact is that PB batteries are as complex as LiPoly batteries and most just do not want to spend the time to learn the difference between AhH rating in big letters(most often a 20Hr. discharge rate),Reserve minutes (most useful for iour purpose),CA / CCA, life cycles at different DOD, how they are rated for number of cycles,etc.

Charles
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Old Apr 24, 2009, 07:52 AM
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Quote:
Originally Posted by everydayflyer

3: You have lots and lots of money and price is no object,see reason #2. If this is the case purchase the largest Lifeline sealed Pb you can justify / carry.


Charles
I disagree... buy a 4S LiFePO 40Ah or so and never look back... Much lighter, but sets you back about 500Eur ...

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Old Apr 24, 2009, 10:18 AM
Southern Pride
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Haralson County GA. USA
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40AH would not be nearly enough for a normal days flying for me.
I agree LiFePO4 would be great but they just cost way to much. My 250 Ahs ( 2X 125) cost me $135 for the pair. They are nearly two years old and I can not tell any difference in their performance but I do need to run a deep cycle capacity test on them.


charles
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Old Apr 24, 2009, 07:08 PM
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Brisbane, QLD, Australia
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Quote:
Originally Posted by everydayflyer
40AH would not be nearly enough for a normal days flying for me.
I agree LiFePO4 would be great but they just cost way to much. My 250 Ahs ( 2X 125) cost me $135 for the pair. They are nearly two years old and I can not tell any difference in their performance but I do need to run a deep cycle capacity test on them.


charles
Charles,

Thank you for your wealth of information. I've done a lot more reading and I think getting a good deep cycle flooded battery and some sort of casing/enclosure to hold them in would be the best way to go for me.

I didn't really know much about car batteries or the difference until I read everything (well, not quite everything) and found the differences. I have a spare car battery at home that I was just "hoping" I could use but on further reading it's quite obvious that if I used it the way I was planning on it would be dead very, very quickly.

I already have a good external charger that I use on the spare car battery, so I can use that with the DC battery. My initial concern was the fact I would have a flooded cell with the possibility of it spilling on a rough ride/inclines etc in the boot of the car on the drive, but maybe I was being over-cautious about this.

Thanks again for all the information - will take a look today at what batteries/enclosures are available at the shops...
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