Help with inverter for mobilty scooter charger. - Page 1
Forum section: electronics / general

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 25, 2019, 05:12:29 pm
content: Merry Christmas to everyone.I'm looking for some advice on charging up a mobilty scooter. I live in a 14 floor tower block, and on the 13th floor. Normally i use the elevator and charge my scooter indoors. But as of two days ago, the water tank at the top of the building ruptured. Hundreds of litres of water got in to the elevator shafts and took out both, so they won't be back in service for a few weeksI've been given a lock up to stor the scooter, but sadly there's no power points in the lock up. I was hoping to use a car battery and inverter to power the scooter charger. The scooter has two 50Ah batteries in series, so the scooter system is 24 Volts. If a car battery and inverter is a viable option, I'm unsure of what capacity car battery that i would need. The scooter charger is an input of 120/230 Volts auto detection, the output is 6Amps / 5Amps at 24 volts. I'm not 100% sure on what power inverter to go for.And also would i need to recharge the car battery after every charge of the scooter via an inverter.This is a bit of a crisis, as i live with my Son, as he's a youngster its unreasonable for me to expect him to run here there and every where. It would be a huge help if someone could suggest a car battery / inverter combination that would be suitable for off the grid charging.Thanks for reading, i could really use the help with this.Thanks again.PS. I have also posted to another forum ( Electronics Point ) If your a member there you probably will see the post / thread.Things are getting a bit desperate now, as my Son is a minor still and can't run some errands like collection of prescription medication i need. The pharmacy won't climb to the top of the tower block i live in.I've no one else to run some of these errands, and trying to come up with a charging solution for the mobility scooter i use. An attachment of the scooter charger is the image posted.I really could use some help. The scooter batteries are 2 x 50Ah 12 Volts in series for a 24 Volt system.Thanks again for reading.

author: Gregg
author_rank: Super Contributor
timestamp: December 25, 2019, 06:01:36 pm
content: Can you take the scooter batteries out, bring them up to your flat and charge them? It seems like you'd have to do similar routine to charge the lead acid battery; not to mention the inefficiencies of that system. If you have to buy both the lead acid battery and the inverter, you might consider purchasing a second set of scooter batteries.What type of batteries are in the scooter? A stand alone battery charger (not built in to the scooter) will certainly be cheaper than a suitable quality inverter.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 25, 2019, 08:41:24 pm
content: 3x Nissan Leaf modules plus a BMS would be a drop in replacement for the stock pack and would be light enough to easily carry.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 26, 2019, 02:49:35 am
content: Thanks for the replys, I'm not sure NiHaoMike what the Nissan and BMS stuff is, or even what it means. The scooter I have as the main daily use is a free rider mayfair. The batteries can be removed, but it's a major undertaking, and beyond what I can manage safely. That scooter has 2 × 50Ah batteries in series, I gather most mobility scooters use a 24 Volt system. I have an invacre Leo pavement scooter, and with my Sons help, the batteries are removable some what easier, all though I can't do this alone (Son at School) yesterday the odds elevator packed up again, just 24 hours or so after being repaired, so now no elevator at all.Ideally I could have got the smaller invacare 36Ah batteries up on a small fold up two wheel trolley, that was the plan until our elevator had been repaired. I would have had to keep my journeys as minimal as possible, not to much of a problem, as the Surgery,Pharmacy, and supermarket are very close by.So I've ordered a good, or best quality inverter I could afford. Its 3000 watt 12 Volt unit modified sine wave. And a 12 Volt 115Ah leasure battery to run the inverter, and an intelligent charger for the charging of the 12 Volt 115Ah battery. I know I've got to get that to a power point some where, my Mothers place is a short taxi ride away.unless the odds elevator comes back to life fairly soon.My plan was to use the inverter, but use an electronic timer to limit charging on a 50% duty cycle so as not to overheat the inverter. Although in the lock up down stairs its freezing this time of year. I was thinking in terms of an analgy, like the battery powering the inverter can only put back power into the scooter batteries no more that it's own capacity. Bit like filling a diving cylinder from a storage cylinder, as opposed to using a compressor. The cylinder filled off storage cylinders can only equal the storage capacity equal to the single driving cylinder. In electrical battery and charging it might be different to the cylinder compressed air analogy.I can keep trips short, and get several, maybe four trips between charges via an 12 Volt battery and inverter. I even considered a small portable generator, but that's no good as I can't leave it unattended.

author: MagicSmoker
author_rank: Super Contributor
timestamp: December 26, 2019, 10:54:15 am
content: Quote from: davelectronic on December 25, 2019, 05:12:29 pmThe size of the inverter is easy: it just needs to be rated for a good margin more than power rating of the charger, or more than 144W (24V * 6A). A 250W inverter should be fine, though it might need to be a pure sine wave type if the charger is power factor corrected.The big problem - quite literally - is that the scooter battery is rated for 24V/50Ah and a typical car battery is rated for 12V and 40-60Ah, or around half the energy storage capacity of the scooter battery (based on a reserve capacity - the time a 25A load can be powered - of 100-140 minutes). At best, then, the car battery + inverter will be able to increase the charge of the scooter battery by 1/3 to 1/2, before factoring in the loss of usable capacity at a high rate of drain due to Peukert Effect.Basically, this idea ain't gonna work unless you have a convenient way of recharging the car battery and if you had that you could just use it to recharge the scooter battery instead. A long extension cord, a solar or wind generator setup, or even a small generator like the one below would be better solutions:https://www.harborfreight.com/900-Watt-Max-Starting-2-Cycle-Gas-Powered-Generator-EPACARB-63025.htmlJust chain the generator to your mobility scooter to secure it, if nothing else is handy.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 26, 2019, 04:04:50 pm
content: Very helpful thank you for the explanation, I've worked out i can charge the battery for the inverter at me Mum's about half a mile away from where i am. Its easier to recharge a storage battery than remove the big mobility scooter batteries. That's a big undertaking virtually impossible even with my Sons help. I've got a lite weight two wheel trolly for the storage battery. This battery is a leasure battery of 12 Volts and a capacity of 115Ah. Its the best i could find brand new and in my budget range. And a reputable company called Halfords here in the UK.The inverter is a modified sine wave type, again i went for a reputable local trader, so if there are issues i can exchange or replace it. Its 3000 watt and modified sine wave type. Really hope it powers the scooter charger. I was going to use a plug in electronic timer to duty cycle the inverter 50% maybe, not perfect for charging, but as a get by for now will hopefully work. Also i will limit scooter use as little as i can, and necessary journeys only. Its not a perfet solution but its all I've got.There is a plan B but the odds elevator needs to be working. And that's remove the small scooter batteries take them up to our place and charge them indoors. The smaller scooter batteries aren't do different to remove, with my Sons help. He's quite a stocky teenager, more than capable of removing the small scooter batteries. The elevators in this place are in a right rough state, eventually these will need a refurb whether are housing landlord likes it or not. The elevators have to comply with HSE regulations here in the UK. So i can for see a future where some alternative charging solution will be needed again.When i moved here some three and half years ago i didn't need a mobility scooter. The scooter was chosen so as to comply with safe weight limit, and physical size of the inside of the elevator.In the last ten minutes my Son has just checked both elevators, and there both down. This a srewed up Christmas and Family i was going to see, but now can not see them.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 26, 2019, 05:20:05 pm
content: Quote from: davelectronic on December 26, 2019, 02:49:35 amThe Nissan Leaf is a popular electric car, its battery consists of many modules each about the size of a textbook. Teardown:A BMS (Battery Management System) basically prevents the batteries from operating outside their safe operating range. Note that the Nissan Leaf cells are LiMn which fully charges to 4.1V/cell rather than the 4.2V/cell of standard lithium ion. Therefore, the built in balancers on the cheap BMS boards would not be very helpful. Use a decent R/C battery charger with balancing functionality.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 26, 2019, 10:26:33 pm
content: That's a lot of battery/Cells, what the heck could he want with that lot. Interesting though, thanks for posting. Yes I didn't give it much thought, but I figure I'm going to need some BMS so as not to run the storage battery to low. Or below its terminal voltage, be ok the high voltage side as the scooter charger does its thing. But I haven't figured in something connected to the battery feeding the inverter. I doubt the inverter knows when to shut off if the voltage drop to around 10.50 Volts, but that's no good letting it drop that low, and risk damaging the battery. I'm in a bit of a hurry so will have to find an off the shelf unit for this BMS.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 27, 2019, 12:38:51 am
content: Quote from: davelectronic on December 26, 2019, 10:26:33 pmLuckily, you can buy just a few modules if you have no use for a whole pack, at a higher price per module of course.https://batteryhookup.com/collections/green-friday-weekend-deals/products/nissan-leaf-battery-module-gen-1The bad news (for us, good news for sellers) is that demand is way up thanks to California.QuoteYou can also look into universal R/C chargers that run on DC. The usual use case is charging R/C aircraft batteries from a larger battery on the ground, sealed lead acid used to be the usual choice but nowadays large lipo packs like a few EV modules or even an array of 18650s are popular. They often do have a programmable input voltage cutoff but I don't think they're really designed to minimize current draw when tripped.I would say return the 3kW inverter if you can and buy a smaller inverter, a DC input universal charger, or even a boost converter module with a current limit. Such a large inverter will almost certainly be operating way outside its optimum efficiency point, which as a rule of thumb is generally within 25%-70% of its rated maximum output. (And that's assuming it's even a decent inverter to begin with - a real 3kW inverter would be expensive.) A 400W unit would give plenty of margin and be operating pretty close to its optimum efficiency point.

author: Terry01
author_rank: Frequent Contributor
timestamp: December 27, 2019, 12:53:55 am
content: The way power chargers for wheelchairs/scooters etc work is they charge the first 80% or so in the first 5 - 6 hours then spend another couple on a lower charge top up and the last little bit on trickle charge.Can't you go round to your mums and leave your chair on charge for the day every 2 or 3 days till your lift is fixed. If you're careful about your usage you should be able to manage your power to get you about till your lift is fixed?

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 27, 2019, 07:08:04 pm
content: Thanks for the replys, i will watch the video later this evening, i have watched some of that guys stuff before.Just picked up the leasure 12 Volt 115Ah battery, the scooter just by a whiskee got me home. On a 60mph road with battery meter lights dropping fast its a little worrying, will it get me back...It was touch and go, the big scooter battery has to be charged now, no exception.Me Mum's place is first floor, even running an extention lead from her flat is a no no. Taking a battery up two flights of stairs on a small sack Barrow is doable with my Sons help. The odds elevator is working again, the charger off Amazon showed up also to day. So charge that up over night, then attempt an inverter solution tomorrow. I just don't want to lower the big leasure battery voltage and end up with a huge door stop.

author: Terry01
author_rank: Frequent Contributor
timestamp: December 27, 2019, 09:48:08 pm
content: http://www.wheelchairdriver.com/is a great site for everything wheelchair/scooter related stuff. Well worth a look if your a wheelchair/scooter user. Click the "forum" button in the top right of the site page. You'll find loads of good stuff there.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 28, 2019, 03:14:06 am
content: That will make an interesting read Terry01, some smart looking mobility aids there. And built by the looks of it by a guy that knows exactly what the disabled need. Thanks for posting the link. One of my biggest problems is the numbers, I'm useless at the maths in electronics. I love the hobby, but my maths handicap is so limiting when it comes to working out what's needed. I can only describe it as a form of dyslexia but with numbers and equations.It really frustrating, I've bought a 1000 watt inverter modified sine wave, and will send the 3000 watt unit back. The 3000 watt inverter was £200, the 1000 watt inverter was £90This is how I saw the maths on the charger for the large mobility scooter I have. Input of 230 VAC at 1.5 Amps, so 230×1.5 = 345 watts being drawn from the scooter chargers primary side. Secondary side of the scooter charger, 24 VDC × 6 Amps = 144 Watts. So which numbers determines ths inverter size ? I would think the primary side numbers of the scooter charger. Also charging the scooter can vary hugely depending on usage, some of my charges have been as short as 15 minutes, other charges have been over 3 hours. How can I know what any given journey will require in terms of charging capacity.And when working out the inverter and battery to power it, I came up with the largest 12 Volt capacity leasure battery i could find an afford. 12 Volts at 115Ah, and using an inverter calculator on power needs, it came up with 33 Amps being drawn from the battery, from first stage of the charge. And the battery would be exusted after 3.5 Hours at that rate. The inverter states a rest period after approximately 60 minutes, as not to completely flatten the battery, I'm going to use a plug in electronic timer to run the charging process at 50% duty cycle. Total 6 hours 3 charging hours 3 resting hours. I've no idea if that's necessary, all I know is I would not want to destroy the inverter, or turn the battery into a large door stop. If my maths where better maybe all the theory side of the numbers would give me the answers I'm looking for.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 28, 2019, 03:37:50 am
content: Quote from: davelectronic on December 28, 2019, 03:14:06 amThat's 345VA, which is not the same as watts. (VA is always the same or higher.) That probably means the charger does not have PFC, which fortunately is no big deal for a modified sine inverter.QuoteThe 60 minute figure is if you're running it at maximum load, if you're running it at 80% or less (rule of thumb) as you'll be doing, it can run continuously.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 28, 2019, 08:40:18 pm
content: For VA i understand with linear transformers and finding the VA i need with regards power. I'm only going to get 3.4 hours charge time according to the online inverter calculator once i put the numbers in. I will charge for 3 hours first, so as not to totally flatten the battery. I've been using the scooter on borrowed time, yesterday i could have easily get stranded. I took a risk on picking up the 12 Volt 115 Ah leasure battery. The extra weight nearly didn't get me home. After resting the scooter batteries they recovered enough to get me home on the pavement at 4mph. Normally I do road and 8 mph, its just quicker to get things done using the road. Me and the scooter are insured for use on uk highway ( Not motorway) . I'm not using it now until i get it charged up.I don't think 3 hours will complete the charge, only because I've never let the batteries drop this low. Normally i charge after every journey, no matter how short or long. I think a second charge afer topping up the leasure battery over night will be needed. Then I'm going to limit and plan short local journeys that are necessary and no extra distance. I should get 4 to 5 short journeys being conservative with the scooter. If i had the extra cash i would have tried to find an even bigger Ah battery, or used a 24 Volt off the grid system, just because its lower current i believe.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 29, 2019, 03:15:35 am
content: Well the 1000 watt modified sine wave inverter does power the scooter charger. I've used a plug in timer to limit the charge time to 3 hours, no breaks. It's very cold out there tonight, I'm fairly sure it won't overheat with that scooter charger load. I was concerned not to kill the battery by pulling to much from it for to long. The battery has a limit of 80 cycles, should keep the scooter going, as long as the inverter lasts.It's easy to see these cheap inverters are made down to a price. You get what you pay for I guess.

author: davelectronic
author_rank: Frequent Contributor
timestamp: December 29, 2019, 07:22:35 pm
content: I thought posting the first charge of the mobility scooter via this batter / inverter system of charging result.Taking a multimeter down to the lock up where the scooter is, disconnected the charger from the scooter, and battery from the inverter. The terminal voltage read 12.09 Volts, before disconnecting the inverter green led was on. So no faults, turning the scooter to on, it was showing all the scooter meters 4 x red led's 4 x amber led's, and 2 x green led's. Fully charged in doors and charged via a 13 Amp socket, there should be 4 x green led's. So i guess close to 3/4 of a charge maybe, its hard to say exactly.Using the online calculator for duration of inverter battery use, it came up with 31 Amps and a time of 3.4 hours. Given the 115 Ah the battery is rated at. I'm not sure if 3 hours inverter time running is to close for comfort.At the moment that charger is reading 12.60 Volts and 7.9 Amps charging current. So hopefully I'm not giving the storage battery to much of a beating.Anyway thought I'd post the results.