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Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

Hi all,

Who here wants my job? - Just kidding, but it's yet another tale of woe I'm afraid.

My mobility scooter battery charger has gone belly up this time. It's a rather neat SCR controlled jobbie, but I haven't a clue where to start when it comes to diagnosing the fault. So far, I can say that the transformer is good, delivering 30V-0V-30V AC for the charging circuit, and 13V-0V-13V AC for the control/processor circuit. The processor would seem to be working, since the 'power' LED is blinking (which indicates a fault). The charge output is to all intents and purposes, nil (about 0.3v) - it should be delivering 24V.

The operating principal is that of multistage charge regulation, being current regulated at the beginning of the charging period, keeping the maximum current to 3A regardless of voltage, becoming voltage regulated as the scooter's battery pack reaches its nominal voltage, and tops out at about 27.6V.

A quick visual inspection reveals nothing, with the PCB's components showing no sign of damage or stress. The output fuse (soldered onto the PCB) is intact, but rated at 20A it is almost eight times the output current (3A) of the charger, and somewhat generously rated I think. . . I haven't delved in any deeper because it's been a long day in town, time is getting late, and it looks like a bit of a fiddly job to dismantle, especially when I'm not feeling up to the task.

I don't really know where to start with this thing, but I did think that it might be a good idea to check the two SCRs, if not for any other reason then because they are the last components ahead of the battery pack, and in my eyes the most vulnerable to careless handling/short circuiting of the output cable - does that make sense? The question is, how do I go about testing the SCRs?

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Topic starter Posted : 29/11/2019 9:28 pm
Nuvistor
(@nuvistor)
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Posts: 4158

Some info for SCR testing, I only ever saw them go S/C and blow fuses, presume you don’t have a circuit for the charger.

Does the charger need a specific load to switch on and are the batteries faulty and stopping it switching on?

Did you get the other car fixed?

http://www.circuitstoday.com/how-to-test-an-scr

Didn't expect it to expand the web page like that.

 

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Posted : 30/11/2019 9:09 am
crustytv
(@crustytv)
Vrat Founder Admin
Posts: 10843
Posted by: @nuvistor

Some info for SCR testing, I only ever saw them go S/C and blow fuses

You or Marion could of course have just looked under the "service dept" section above (Sadly very few do, so you're not alone), under "general tips". The service dept section not only offers free-to-view data and stock faults but countless other tips and how to's relating to the hobby, including how to test a Thyristor(SCR). 

https://www.radios-tv.co.uk/test-a-thyristor/

Posted by: @nuvistor

Didn't expect it to expand the web page like that.

The reason why the link you provided expanded to look pretty, is covered here

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Posted : 30/11/2019 10:23 am
Nuvistor
(@nuvistor)
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Posts: 4158

Hi Chris,

I tend to do a web search first, will the search facility at the top of this page search the whole site or just the forum?

 

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Posted : 30/11/2019 10:26 am
PYE625
(@pye625)
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Posts: 4980

Hi Frank, I kind of answered that question in my ramblings of the Pam TV thread.

In fact, I now find it a very useful search function. I too previously automatically did a general google search whilst overlooking what is right in front of us here on this site. ? 

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Posted : 30/11/2019 10:36 am
crustytv
(@crustytv)
Vrat Founder Admin
Posts: 10843
Posted by: @nuvistor

will the search facility at the top of this page search the whole site or just the forum?

?

https://www.radios-tv.co.uk/community/faq-members-only/improved-search-for-forum-and-blog/

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Posted : 30/11/2019 11:23 am
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

@nuvistor

Hi Frank,

Cheers for that! - I'll be taking a closer look at this thing pretty soon, but, straight off the bat, unfortunately, no I don't have the circuit for it, but then it's never given me any need to look for one, though I might have to now. With regard to the batteries, they're in tip-top condition, brand new "Yuasa" only four months ago. The charger was working correctly up to disconnecting from the batteries that morning, but then flashed the "fault" warning when reconnected after returning from town that evening.

Unfortunately, it was my friend who disconnected it in her eagerness to be helpful (hence the comment about potential shorting out of the output lead). She's not the most astute individual regarding the correct procedure. Thankfully, I have more than one scooter, and more than one charger, but it's not good practice to "time-share" a charger, neither for the batteries, nor the charger. I did however use the other charger to bring the batteries up to a full charge overnight, so I think we can say the batteries aren't likely to be the issue, and in any event, they worked perfectly well all day in use.

With regard to load sensing, true, most chargers do need to be connected to the batteries before the charging circuit turns on, and that may even be the case with this charger, however, under a "no fault" condition the self-test feature would still return a steady red, even without the batteries being connected, but as it stands, there is only a rapid blinking red, which according to the decal on the front panel, indicated a fault within the charger. I did consider the possibility that there may be a temperature sensor somewhere in the charger, and brought it indoors (normally lives in the garage) overnight, and tried it again this morning - same fault indication.

The lamp states are; 1, Steady red = power on, charger normal. 2, Flashing red = power on, charger fault. 3, Steady red + Flashing green = power on, batteries charging. 4, Steady red + Steady green = power on, batteries fully charged and floating.

The charger, for anyone interested in following along, is a Pihsiang Model MB-24/3 - Not to be mistaken as a cheap effort, and not cheap to buy at about £75.00 for a new one! - I have however, found a few used ones (four or five) on eBay, priced around £45.00 apiece, so definitely worth repairing. In amongst my other activities this evening, I'll be searching (loathe to say Googling!) for any information on this charger, and at some point, though not tonight, will dismount the PCB and explore a bit more.

The car? - (Sylvie). . . . . I have a new pair of headlight bulbs to fit, and the alternator will be fitted on Wednesday afternoon, another £50 (on top f the price of the alternator) I'm afraid, but that's how it goes these days.

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Topic starter Posted : 30/11/2019 10:33 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

@crustytv

Hi Chris,

I reckon you're right, but my noodle box seems to like to fart and sit on its bum quite a bit just lately, and in fairness, it was a long day and I was about done in after my venture into town. ? ?

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Topic starter Posted : 30/11/2019 10:40 pm
Marconi_MPT4
(@marconi_mpt4)
Reputable V-Ratter Registered
Posts: 348

Hi Marion,

We used to have a number of these lurking in the factory until the company was acquired and moved to a new site just over two years ago. Unfortunately everything not required at the new site was scrapped under '6S' rules! I am guessing your scooter has an electronic motor control power module that might be a Penny & Giles Solo or S-Drive.

Very little technical information exits on the 'tinternet for the Pihsiang MB-24/3 charger. However this thread might be of interest but seems to fizzle out as to the exact cause of this error state.

https://forum.allaboutcircuits.com/threads/mobility-scooter-power-supply-repair.13256/

My guess is there may be dry joints but also check the current monitor circuit where a low resistance sense resistor or resistors in parallel may be open circuit.

Rich

 

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Posted : 01/12/2019 1:40 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5477

Does it have to be an exact replacement charger, Marion? Because there must be several suppliers of multi-stage 24V SLA chargers out there.

Not much saving on an original, but have a look here:
https://www.simplypowersupply.com/Battery-Chargers/24Vdc-Battery-Charger/default.aspx

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Posted : 01/12/2019 2:33 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered
Posts: 1745

Some of those chargers won't start charging unless the battery has some voltage left in it, I can recall having to 'kickstart' the charger with another charged battery temporarily connected across the one needing charging, this was one of those Gel type SLA types.

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Posted : 01/12/2019 5:06 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5477

I've seen the above twice. Once on a bog-standard battery charger that was converted to a "constant voltage" charger with the aid of a Maplin(?) kit - it needed the battery to be able to power the module first before it'd energise the relay that did the charge switching. The next time it was my fancy CTEK charger which took umbrage at a flat battery - but giving that battery a kick from a 12V 10A linear PSU (tweaked to 13.8V) for a few hours fixed that as well.

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Posted : 01/12/2019 5:56 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

@marconi_mpt4

Hi Rich,

I was looking at that thread last night, and as you say, it just seems to fizzle out with something like "I refitted all the silicon I had taken out - and now works fine". So fingers crossed, mine might be as easily pleased, but as you can see, there is some degree of destruction required to get the PCB out, or is there? I'm pretty certain that with care and diligence it should be possible to dismount the PCB from the heat-sink/bracket whilst keeping the facia unmolested.

There is a low Ohms/high Wattage resistor, prominently placed close to the output terminals on the PCB, and it will be looked at in due course.To be honest, the board looks as good as new, though we all know that counts for nothing!

The motor control unit on the scooter is, I believe, an S-Drive, but it's buried behind the belly pan, under the scooter deck, so I haven't ventured to look any closer - "While it's working, leave it alone" as my dad always said.

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Topic starter Posted : 01/12/2019 9:46 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

@cathovisor

Hi Mike,

It can be any suitably powered charger (not more than 3A), though what I was getting at last night, was the worth of the thing if it were working. Personally, I prefer the older (transformer) types which as a general rule give less trouble - says I with tongue in cheek! ?

The main point to bear in mind is that a charger of greater output current can significantly shorten the life of the batteries (my Pride G0-Go uses circa 18Ah) - the Pride Celebrity, 'big beast' has 50Ah batteries and is happy with an 8A charger.

As chance would have it, I found another MB-24/3 on eBay, or moreover, an MB(E)-24/3 - the former being 'off board' and the latter being 'on board'. They are identical in all respects except that, the MB has a fixed mains lead, fixed input voltage, a carry handle, and the output lead terminates in an XLR plug. The MB(E) has a standard "kettle" cable, selectable input voltage (115/230), no carry handle, and its output lead terminates in a three point blade connector. Electronically, they're exactly the same.

So, on eBay at £29.99 and free postage, I nabbed it late last night. I have two plans in mind; 1, use the eBay one as a test bed/comparison whilst working on my own and; 2, if all else fails, swap the cables and handle from mine to the eBay one, and carry on as if nothing had ever happened! ?

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Topic starter Posted : 01/12/2019 10:16 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered
Posts: 5477

@katie-bush

Sounds like you have a plan there, Marion 🙂

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Posted : 01/12/2019 10:31 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator
Posts: 4884

@red_to_black

Hi R2B,

That's absolutely correct, and in most cases the threshold is 8V per battery (16V per battery pack). Below 16V the charger won't 'open up' to charge the batteries. In theory, you're meant to get the batteries tested and 'conditioned' by your local mobility shop - Aye, and the reply is always "Nah, sorry, they're goosed. . . You'll need some new ones". Quite correct though, you can trick the charger by jumpering in a good pair of batteries, however, the scooter's "ECU" for want of a better description, shuts down at around 18V to prevent excessively draining the batteries.

In any case, my second charger had no issues with recharging the batteries, which were still at around 22V when I had done with them on Friday afternoon. Not forgetting also that the charger was indicating a fault condition, even without the batteries in circuit.

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Topic starter Posted : 01/12/2019 10:33 pm