street
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Aug 27, 2014 17:49:31 GMT
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I've been thinking about one of those battery booster things to start cars with flat batteries or that need a bit of cranking to get going. Would be very useful. I started thinking about making one.
I have an electric wheelchair in the workshop which I'm turning into a general workshop mule, it will be for lugging heavy things around (and for me when I can't be bothered to walk around the complex!), think miniature forklift without the reach. The plan is to make it remote control and build a trailer for it that can fit axles, gearboxes engines etc in, which I've started doing.
Anyway, I thought maybe I could have the thing equipped to start cars with as well. It's 24 volt (2x 12v batteries) so I'm thinking I need to have it switchable down to 12 volts for a start.
I've seen 24v > 12v converters online. They come in a range of amps from 5 up to 80. I'm guessing I need something that at least matches a car battery's amperage, but my question is, if I went for an 80A voltage dropper, would it be safe to use on smaller batteries, say 45A?
Also, since the higher amperage converters are a bit spendy, where might I find something that will do the job out in the wild? Do any commercial vehicles have a 24v > 12v voltage dropper with suitable amperage as part of its original equipment? What about a military vehicle? Generators?
Thanks for your thoughts!
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colnerov
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Aug 27, 2014 19:15:06 GMT
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Hi, instead of going to the bother of converters, why not just connect the leads to either the first batt for 12v or the second batt for 24v? Or if access is difficult wire up 3 terminals Neg, 12v or 24v or 2 sockets and have the leads with a plug? I think you are over thinking it.
Colin
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Aug 27, 2014 19:18:54 GMT
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As above why not just connect one battery so that you have 12 volts but an electric wheel chair battery will not have enough reserve ampage output to jump start a car without draining the wheel chair battery. But the theory is a good idea.
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Last Edit: Aug 27, 2014 19:20:55 GMT by Deleted
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street
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Aug 27, 2014 19:25:43 GMT
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Hi, instead of going to the bother of converters, why not just connect the leads to either the first batt for 12v or the second batt for 24v? Or if access is difficult wire up 3 terminals Neg, 12v or 24v or 2 sockets and have the leads with a plug? I think you are over thinking it. Colin I thought the combined power of two batteries would give greater cranking amps? Maybe I'm not understanding it fully, I'm a little out of my depth here. The batteries are big, the chair has a 20 mile range with an all-up weight of 350kg, so I assumed it had plenty of power. My thinking was, 24 volts reduced to 12 but with the combined amperage of both batteries, regulated by the voltage reducer (say about 80A). Would this not give me an advantage over just one 12v battery connected to the car? Or am I missing something?
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Last Edit: Aug 27, 2014 19:28:08 GMT by street
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Aug 27, 2014 19:35:12 GMT
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What you could do is connect both batteries in parallel which will still give you 12 volts output but the amperage of both batteries this would involve two sets of leads and two sets of connections, both positives to the car battery, one neg to the car battery and the other neg to another earth point on the car will reduce the possibility of a surge but you run a high risk of damaging ECU's on modern cars and save all the hassle and cost of voltage droppers which won't work as you need more than 12 volts to start a car and 80amps is nowhere near what you need to start a car. a decent professional jump pack will be around 1400amps peak.
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Last Edit: Aug 27, 2014 19:37:07 GMT by Deleted
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
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Club RR Member Number: 34
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Making A Battery Booster PackDez
@dez
Club Retro Rides Member 34
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Aug 27, 2014 19:45:38 GMT
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be aware cold cranking amps and amp-hours are two totally different characteristics when it comes to batteries. id expect the battery in an electric wheelchair to be like a leisure battery, i.e. low output over a long period, to give range. which means hgh AH but low CCA.
to start a car you need the exact opposite high CCA (the one to start my pickup is over 750cca for example) but only for a very short period.
most batteries do one or the other, not both.
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colnerov
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Aug 27, 2014 19:47:58 GMT
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Hi, it depends on the Amp/hr of the batteries and how they are connected. If they are for arguments sake 40amp/hr batteries connected in series they will give you 40 Amps for an hour at 24v, if they are connected in parallel they will give you 80 Amps for an hour at 12v. The same with the CCA (cold cranking Amps) which could be say 150 Amps for a shorter period usually 6 to 10 secs before it starts to drop off. It all depends on the specification of the Battery. As said gel type batteries for wheelchairs are not designed to provide high currents for long. Lead acid batteries do that best.
Colin
P.S. they beat me to it!!
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Last Edit: Aug 27, 2014 19:50:10 GMT by colnerov
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street
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Aug 27, 2014 19:54:33 GMT
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I see I see, thanks now I'm getting it. I didn't realise those proper jump packs had so much power. So connecting the btteries in parallel sounds good, though it sounds like my creation will do a poor impression of a proper jump pack!
That said, I have a couple more 12v batteries I could chuck on. I'm guessing more is better when it comes to putting them in parallel.
So if I put 4 12v batteries on this thing, and switch between running them in parallel (for starting cars) and in series (for the 24v motors on the chair), is it possible to use all 4 batteries for the 24v system or can I only use two 12v batteries? Can you pair batteries and then run them in parallel I suppose is what I'm asking. Sorry for all the questions!
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street
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Aug 27, 2014 20:00:14 GMT
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be aware cold cranking amps and amp-hours are two totally different characteristics when it comes to batteries. id expect the battery in an electric wheelchair to be like a leisure battery, i.e. low output over a long period, to give range. which means hgh AH but low CCA. to start a car you need the exact opposite high CCA (the one to start my pickup is over 750cca for example) but only for a very short period. most batteries do one or the other, not both. Oh I didn't see this while I was replying to Colin. I see, thanks for the explanation. It sounds like my idea is a non-starter (badum-tssh). I'd like to read up on the different battery types and understand what makes them high or low AH/CCA. Thanks for the input all, i'll do a little research
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colnerov
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Aug 27, 2014 20:13:04 GMT
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Hi, you will need pretty big switches to cope with cranking current, the obvious and cheapest way is starter solenoids but they don't like being energised for long periods as they overheat. You can connect as many batteries as you like in parallel or series or combinations. But be aware that when in parallel if one of the batteries is weak the stronger ones will try to charge it and so run themselves down, you then end up with all the batteries flat. Sorry to put a dampener on this.
Colin
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Aug 27, 2014 21:15:12 GMT
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When I was working in trucks we had a trolley with three or four truck batteries strapped to it, those and some jump leads would start anything.
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street
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Aug 27, 2014 23:40:41 GMT
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Before I write this idea off totally, I wonder if it might be better to use high cranking Amp batteries instead of the deep cycle leisure batteries that Dez pointed out it will probably have. I'd compromise on range, but perhaps it doesn't need the range so much anyway. I'm thinking two 24V batteries (the guy opposite my unit breaks diggers conveniently so no bother finding those) wired in parallel for the cranking duties, then knock it down to one battery to run the wheelchair motors. Or even cram two 12v leisure batteries on the rig as well as two 24V truck batteries and use seperate circuits for each... Best of both worlds. Hmmm!
Thanks for the heads up on the switches Colin, maybe I can source some switches from the digger guy as well.
Valuable information guys, thanks!
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Aug 28, 2014 10:42:51 GMT
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The idea of having two separate banks of batteries, one for the wheel chair power and other to do the jump starting will work well especially if they are decent truck batteries wired in parallel to provide 12V to jump start as long as you can keep the truck batteries on full charge which will mean plugging it in every night to a charger (another cost to think about) that will maintain the batteries but not overcharge them. Another thing to bear in mind is how close you need to get to the stranded car and you will need heavy duty leads so that there is no current draw lost through the leads, good quality heavy duty leads are not only heavy but are also costly. Personally my thoughts are your idea is great in theory and can work but it will be a lot easier and practical to buy a decent jump pack and possibly not far of the cost of making your set up.
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street
Posted a lot
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Aug 28, 2014 21:02:00 GMT
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The idea of having two separate banks of batteries, one for the wheel chair power and other to do the jump starting will work well especially if they are decent truck batteries wired in parallel to provide 12V to jump start as long as you can keep the truck batteries on full charge which will mean plugging it in every night to a charger (another cost to think about) that will maintain the batteries but not overcharge them. Another thing to bear in mind is how close you need to get to the stranded car and you will need heavy duty leads so that there is no current draw lost through the leads, good quality heavy duty leads are not only heavy but are also costly. Personally my thoughts are your idea is great in theory and can work but it will be a lot easier and practical to buy a decent jump pack and possibly not far of the cost of making your set up. Thanks for your thoughts on this. I think if I can get the truck batteries for a reasonable price I'll give it a go the way you describe above, and see what happens! I'll see if I can find some suitable cable somewhere and crimp my own crocodile clips on the end or something, or maybe have a look around the army surplus store. It won't be used all that much, my workshop isn't big enough to warrant a machine like this but for the novelty and for jumping the occasional heap it's worth a go I think. Will let you know how I get on! Edit- Just re-read your cautions about the cables. Might have to be a bit more serious about them, not really something I should cut corners with. I'll see what I can find second hand.
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Last Edit: Aug 28, 2014 21:05:19 GMT by street
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Aug 28, 2014 21:59:49 GMT
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Good luck with it, I'm genuinely interested in how you get on with it so please keep us informed. The battery cabling off the diggers should do the job if its long enough or if you have a local commercial breakers local try them.
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Sept 2, 2014 11:10:38 GMT
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Leonard Cohen approves. *n
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Top grammar tips! Bought = purchased. Brought = relocated Lose = misplace/opposite of win. Loose = your mum
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Sept 2, 2014 11:45:30 GMT
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Sept 2, 2014 17:35:04 GMT
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The idea of having two separate banks of batteries, one for the wheel chair power and other to do the jump starting will work well especially if they are decent truck batteries wired in parallel to provide 12V to jump start as long as you can keep the truck batteries on full charge which will mean plugging it in every night to a charger (another cost to think about) that will maintain the batteries but not overcharge them. Another thing to bear in mind is how close you need to get to the stranded car and you will need heavy duty leads so that there is no current draw lost through the leads, good quality heavy duty leads are not only heavy but are also costly. Personally my thoughts are your idea is great in theory and can work but it will be a lot easier and practical to buy a decent jump pack and possibly not far of the cost of making your set up. Thanks for your thoughts on this. I think if I can get the truck batteries for a reasonable price I'll give it a go the way you describe above, and see what happens! I'll see if I can find some suitable cable somewhere and crimp my own crocodile clips on the end or something, or maybe have a look around the army surplus store. It won't be used all that much, my workshop isn't big enough to warrant a machine like this but for the novelty and for jumping the occasional heap it's worth a go I think. Will let you know how I get on! Edit- Just re-read your cautions about the cables. Might have to be a bit more serious about them, not really something I should cut corners with. I'll see what I can find second hand. We used 500amp welding cables ....... But then we used to have a free supply at work to use......
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Sept 2, 2014 18:22:22 GMT
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When I was working in trucks we had a trolley with three or four truck batteries strapped to it, those and some jump leads would start anything. You could probably weld with that much power too if push came to shove!!! In all honesty 1 truck battery if it doesn't have a blown cell and is reasonably healthy will start just about anything you can think of - they aren't cheap mind even knackered they are worth a fair bit as scrap due to the weight. The local car auctions used to have one permenantly strapped on a sack barrow with thick jump leads bolted to it then clipped onto a bit of timber (one on each side) when not in use. It used to start everything with a dodgy battery every auction - never saw it fail. You want proper THICK cable thats what will make a difference as well. Anything you can crimp a connector onto isn't upto the job - you'll need to solder them on really probably using a blowlamp to get everything hot enough. As an aside I've seen a car jump started using 2 bits of thick welding rod from an 18v dewalt drill battery pack!!!
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street
Posted a lot
6.2 ft/lbs of talk
Posts: 4,662
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Sept 2, 2014 22:56:42 GMT
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This is all good information guys. I should be able to borrow at least one digger battery to test the theory and it won't be won't be too hard to sort a bigger or secondary battery tray. Here's the thing in question: Took it to the gathering where it was given a good thrashing around the campsite for 2 nights, and it still had half battery life by the end! So given how good a range the two leisure batteries have, I'm thinking one or two truck batteries might still give it fairly good range. The forklift needs charging every day after all. Also, going to put that ram that used to lift the seat and the seat frame to use. I'm going to find out if it's more efficient to run a hydraulic pump and ram instead of that electric one, although it can apparently handle 125kg. Anyway, first things first. The jumper pack. I'll start a thread for it in the Reader's Other Modifications section and I'll put all this info to use
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