Clifford Stone Posted October 30, 2012 Share Posted October 30, 2012 Feel a bit foolish on this one, however I dont know . . . so I'm hopping some one can hold my hand and point me in the right direction? I just cant get my head around amps and ohms! For field charging this is the quad charge I have: **LINK** It will be required to charge at 1C rate, 4 to 6 batteries in the course of a day, not all at the same time? 2200mah 4S 14.8v, these batteries will have been discaharged in flight to around 50%. Probably not more than 2 may be adding a third after a race? In fact they will all be added at intervals, may be 15-20 mins? Obviously I need a 12v battery. One is looking at Gel or matenance free type, prefering Gel, despit the cost! I want to keep it all as compacked and light as possible . . . a 75ah battery would be an ideal 'physical size' . . . but is that enough to provide the power I need for the day? Need I go to 100ah plus? Sorry, I'm so thick sometimes . . . CJS Edited By Clifford Stone on 30/10/2012 18:26:27 Edited By Clifford Stone on 30/10/2012 18:27:10 Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted October 30, 2012 Share Posted October 30, 2012 Cliff, - One way of looking at this is to calculate some watt hours. The 12V, 75Ah battery, fully charged: So that's 12 by 75 = 900 watt hours. (Wh). Your 2.2Ah lipos, 50% discharged. So to recharge: 1.1 by 14.8 = 16.28. Then by 6, for 6 batteries, = 97.68. Say 100Wh. Now add 50% to run your charger. So that’s 150Wh total, to recharge six packs, give or take. 900Wh divided by 150Wh = 6. So your 12 volt might, in theory, recharge your flight batteries six times before it needs charging. So if you are prepared to recharge regularly this will be fine, I reckon. Good Charging...... PB Edited By Peter Beeney on 30/10/2012 19:17:13 Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted October 30, 2012 Share Posted October 30, 2012 Glad I refreshed before I posted, now I've deleted what I wrote 'cos Peter beat me to it. Yep, in theory there's 6 days flying in your 75Ah battery. However just bear in mind that it is advised that you shouldn't discharge a Lead Acid battery much more than half way, and certainly not store it below half discharge. So, the 75Ah will be plenty, but I'd top it up ASAP after a days flying. Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 30, 2012 Author Share Posted October 30, 2012 Posted by Peter Beeney on 30/10/2012 19:15:33: Cliff, - One way of looking at this is to calculate some watt hours. The 12V, 75Ah battery, fully charged: So that's 12 by 75 = 900 watt hours. (Wh). Your 2.2Ah lipos, 50% discharged. So to recharge: 1.1 by 14.8 = 16.28. Then by 6, for 6 batteries, = 97.68. Say 100Wh. Now add 50% to run your charger. So that’s 150Wh total, to recharge six packs, give or take. 900Wh divided by 150Wh = 6. So your 12 volt might, in theory, recharge your flight batteries six times before it needs charging. So if you are prepared to recharge regularly this will be fine, I reckon. Good Charging...... PB Edited By Peter Beeney on 30/10/2012 19:17:13 ??? . . . sorry Peter, I realy have a problem with numbers, and spelling, you may have noticed . . . however, I think you are saying, 6 packs, 50% discharged, will, in theory, recharge 6 times ie., 6x6 from a 75ah 12v battery . . . Sorry to be so thick but its not a good day for the grey matter . . . my one cell has been over stretched trying to understand this on my own. So, if I have got it right a 75ah 12v. Gel battery will do the business, with plenty to spare? CJS Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted October 30, 2012 Share Posted October 30, 2012 Sorry Cliff, my sincere apologies, I didn’t think.. Yes, in short, your 12 volt will recharge your flight batteries 6 times on one charge. Even if you are very cautious and call it 5 times for one day you will still have plenty in reserve. The most important thing is to keep that battery fully charged. It’s very easy to over estimate how long the battery will last, I saw a man struggling with his field charging 12 volt car battery recently. It was reading 10 volts when I checked, and he couldn’t remember when he last charged it!! What sort of charger are you using? There is a PSU, (Power Supply Unit), with an output of 13.8 volts. If this maintains a genuine 13.8 volts this would be an ideal charger. You can leave it connected indefinitely and this would be the best way of keeping it good condition. I’ve had no experience of these PSU’s, but I’ve done plenty of swanning around the man sized (proper!) units in the past. Anyway, enough of the headache stuff for the moment. Have a think on this, and come back here about the charger later. It’s shocking stuff to work with, this electricity…… PB Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 30, 2012 Author Share Posted October 30, 2012 Hi gents, and thanks for you patients and help . . . it gets realy frustrating at this end as well, trying to make sence of figures, especialy on a bad day! Any-old-how, things have moved on a little since I posted the above. I have a source of used deep cycle gel batteries, you know the type, they have a life of 10 years, are put in as back up on serious security systems and the like. They change them once a year as a matter of course, because of the security risk. My source takes xxxno. as a job lot at these change overs I now have the chice of a 75ah or a 112ah unit. I take a chance, but at about one third of the cost to new and no worries about acid sloshing about, its a no brainer. You have confirmed a single charge life of the 75ah, so obviously the 112ah is considerably more, I have three days racing in mind at the Nats next year?? . . . If I can work out some form of bed on the camp site??? Caravan/camping gear long gone. Chargin . . . about time I had a new charger, my very old Halfords unit is not going to cut the mustard, I thought one of these: **LINK** Anyone got any thoughts? CJSF Quote Link to comment Share on other sites More sharing options...
Welshboy Posted October 31, 2012 Share Posted October 31, 2012 I have the same quad charger. Instead of buying a specific gel cell charger, I bought a mains power supply unit to feed the quad charger and use that to charge my gell 12v. This way I can also charge my lipos at home. Quote Link to comment Share on other sites More sharing options...
Alan Randall Posted October 31, 2012 Share Posted October 31, 2012 Cliff, Before you part with your £30 at Halfords, check out your local Aldi supermarket. I bought a charger looking very much like that one for about £13. about 2 weeks ago. Alan Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 31, 2012 Author Share Posted October 31, 2012 Posted by Welshboy on 31/10/2012 06:28:12: I have the same quad charger. Instead of buying a specific gel cell charger, I bought a mains power supply unit to feed the quad charger and use that to charge my gell 12v. This way I can also charge my lipos at home. Yes Welshboy, I have a power supply too, which will be very useful for 'bulk' home charging of all my batteries. But my spacific needs are 'on field' charging when racing, so I have to cover both senarios. CJS Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 31, 2012 Author Share Posted October 31, 2012 Posted by Alan Randall on 31/10/2012 09:07:59: Cliff, Before you part with your £30 at Halfords, check out your local Aldi supermarket. I bought a charger looking very much like that one for about £13. about 2 weeks ago. Alan Alan, thanks for the 'heads up', I am going to the town this PM, I will pop into Aldi, have a look-see? CJS Quote Link to comment Share on other sites More sharing options...
Olly P Posted October 31, 2012 Share Posted October 31, 2012 Clifford - can your lipo charger not do Pb cells too? therefore charge your field source using the thing it will power at the field. I use 4s Lipo's as power sources to charge my 3s flight packs! Mostly as the aircraft the 4s packs are for isn't quite finished yet - need to balance it better.... Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted October 31, 2012 Share Posted October 31, 2012 Clifford, If your SLA (Sealed Lead Acid) battery is second hand you need to check it out. If you have a voltmeter, very necessary for serious electric flying I’d have thought, try the open circuit voltage. If it’s below 12 volts you might have a problem. Ideally it would want to be around 12.3 volts. Put the charger on and if the voltage rises fairly quickly that also might not be an ideal situation. Lastly, and most importantly, if your LiPo charger will discharge plumbum, or Pb, or lead cells, do a test a test discharge. If you don’t do this, then I’d consider all bets are off. If your charger doesn’t do lead, perhaps someone would do it for you. It could change your flight pack charging regime. If there is 50Ah capacity then you would only recharge 4 times. If there were 25Ah then it’s only 2 times; and when the battery gets in this condition there could suddenly be nothing left; it would be on it’s very last knockings… I’m always being given batteries of all sorts, on the basis ‘ that they may do someone a turn’. This happened again a fortnight ago, a large square Yuasa 12 volt lump in good nick, labelled 24Ah. It looked ‘as new’. Ex golf buggy. The open circuit voltage was 12.2, so a good start. But when I gave it a test discharge it came back with less than 3Ah, totally useless. And in my experience I’ve never been able to effect any sort of recovery on these gel cells. Hope this is of some use. PB Quote Link to comment Share on other sites More sharing options...
John Cole Posted October 31, 2012 Share Posted October 31, 2012 Posted by Chris Bott - Moderator on 30/10/2012 19:25:21: However just bear in mind that it is advised that you shouldn't discharge a Lead Acid battery much more than half way, and certainly not store it below half discharge. What CB says is correct for car-type batteries, but leisure batteries are designed to accept deep discharge. Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 31, 2012 Author Share Posted October 31, 2012 The batteries I am refering to are fully sealed 'Gel type', they have a 10 year life, were instaled only as back ups in highly sesative security situations. Being changed as a mater of course at majour service points, possibly never having been used to power anything? Checked befor sold, but obviously there is no GT. They are not like buggy batteries, continualy used and recharged, they are bigger, maintained with a continus trickle charge 'just in case'. Buggy and mobility types use up their charge cycle allocation then outed. I went to the tip yesterday to dump 2 dead, lead acid jobies. There were half a dozen pristin looking 12v, 20/30ah buggy types, one was tempted? . . . but as has been mentioned, they are so often at the end of their useful life. I believe modern battery technology has a 'charge number limit' of 250-500'ish? However, all that said, for warned is for armed, I will take my meter with me. CJS Edited By Clifford Stone on 31/10/2012 12:41:08 Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 31, 2012 Author Share Posted October 31, 2012 Posted by Olly P on 31/10/2012 10:43:18: Clifford - can your lipo charger not do Pb cells too? therefore charge your field source using the thing it will power at the field. It proberbly does? . . . but I have no idea how to interprit the instructions??? thick'o Im afraid I have to rely on being told . . . there is only me, so I dont have much chance other than forums . . . CJS Quote Link to comment Share on other sites More sharing options...
Peter Beeney Posted October 31, 2012 Share Posted October 31, 2012 Yes, indeed some ME batteries can be very good value. However, just because a cell is continuously in a float condition doesn’t necessarily mean that it doesn’t deteriorate. I can quote some examples where SLA cells have gone open circuit in these circumstances and of course this would not be noticed until the power supply failed. These were all well within spec. and time limit, and also in the most cosseted environment possible; and when this happened it did not go unnoticed!!! However, fortunately this is not a life or death situation, the worse that can happen is that your charger simply decides to go slow on a low voltage supply. At least it won’t cause your models to crash….. PB Quote Link to comment Share on other sites More sharing options...
Welshboy Posted October 31, 2012 Share Posted October 31, 2012 I meant to say that I use my quad charger to charge my 12v gell lead acid deep cycle battery. Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted October 31, 2012 Author Share Posted October 31, 2012 Posted by Welshboy on 31/10/2012 18:47:38: I meant to say that I use my quad charger to charge my 12v gell lead acid deep cycle battery. I am going to have to look very closly at the instructions on my charger??? The problem I seem to detect as I read the specs., on chargers is an 'ah' size limit??? The one I'm looking at tomorrow is 112ah, I dont want to blow my nice shiney new quad charger before it has even started the job it was intended for?? CJS Quote Link to comment Share on other sites More sharing options...
Olly P Posted November 1, 2012 Share Posted November 1, 2012 Should be OK Clifford - But I don't have a charger of this flavour, so maybe a new thread asking about the charger capability for lead acid charging? And how to? Olly Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted November 1, 2012 Author Share Posted November 1, 2012 Well the deal is done, I plumped for the 75ah battery, 6x6 = 36 charges. Thats the Nationals covered provided I take 4 fully charged batteries to start Saturday off. I suspect I will have more than 4 race batteries befor then anyway? Checking out this years Nats results, each competitor flew 14 races over the weekend including, plus the finals for the few. The battery showed 13v. on the meter, it cost £30 . . . a fair gamble?? CJS Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted November 1, 2012 Share Posted November 1, 2012 Sounds a good buy Clifford, time will tell. Quote Link to comment Share on other sites More sharing options...
Shaunie Posted November 1, 2012 Share Posted November 1, 2012 I regard any 12v lead acid below 12.6V as only partially charged. Many SLA and Gel type batteries have a charged open circuit voltage up to and occasionally exceeding 13V (I have a couple in the workshop that have not been charged for some weeks and give a terminal voltage of 13.1V). I would think it unlikely that a battery supplying a LiPo charger could ever be too big, the charger will only ever draw the current it requires. Batteries on permanent float charge are eventually damaged by it, but this does take several years to happen (typically they are end of life after 4-8 years depending on float voltage and battery quality). I think if the battery has only been in service for a year it will be fine, if its a Hawker, Optima or similar it will probably last you nearly forever If you have a power analyser discharge th.e battery through it (into a headlamp bulb for instance) down to 10.5V and measure what its capacity is that way. Quote Link to comment Share on other sites More sharing options...
Clifford Stone Posted November 2, 2012 Author Share Posted November 2, 2012 Posted by Chris Bott - Moderator on 01/11/2012 20:14:53: Sounds a good buy Clifford, time will tell. . . . ???? as you say Chris, 'time will tell' . . . ? So far, I have had the best week for true good luck for many, many years . . . CJS Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.