Jaycar MB-3612 charger

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drowe67
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Jaycar MB-3612 charger

Post by drowe67 »

Hi,

I am doing a Charade conversion using 12 x 12V Optima Yellow Tops AGM batteries. I am considering using 12 Jaycar MB-3612 chargers, one for each battery.

I would appreciate any comments on using these chargers - in particular from anyone that has used them (or something similar) for an EV.

Here is the plan:

1/ The MB-3612 chargers cost about $79 each in quantity, or around $950 total. This is pretty cheap compared to the one-big-charger and shunt (i.e. Rudman) regulator approach that I would otherwise need for my AGMs.

2/ They are 85% efficient switch mode chargers, weigh about 800g each, and charge at 12A which is fast enough for my purposes. Each charger is about the size of a large paperback, so squeezing them into the Charade should be do-able.

3/ As I am using sealed AGMs I need some form of per-battery charge control to equalise the charge and prevent over/under charging. Using one charger/battery achieves this. The maximum (bulk charge) voltage is 14.5V which is around that recommended for Yellow Tops.

4/ Using multiple chargers has one weakness - if a charger fails you can drive off with 11 full and 1 discharged battery, causing possible damage to that battery. So I intend to build a gadget to monitor the voltage of each battery from the dash, so I can determine if a charger fails and a particular battery has not charged.

5/ I have purchased two chargers to test the idea, however there was a trap I discovered:

Like a lot of high-ish current switch mode power supplies (e.g. laptop power supplies) the AC ground is directly connected to the negative lead of the charger. So if several of these chargers were connected across a series string of batteries the - and + terminals of the batteries would effectively be shorted via AC ground which could get kind of exciting!

AFAIK the ground connection is mainly to reduce radio Frequency (RF) noise from the charger rather than a safety concern - as in most switch mode power supplies the AC side is isolated from the DC via a transformer, hence the DC side is "floating".

So to test the idea here is what I did:

1/ Made up a short AC extension cord with a broken ground lead. Connected charger A to this to fully isolate the DC side.

2/ Made a series string of two batteries with a jumper lead.

3/ Connected chargers A & B to battery one and two.

4/ Tentatively plugged it all in and switched on.

All went well - both batteries charged OK from the two chargers. I left it running for a few hours and no obvious ill effects, battery voltage in float charge mode was about 13.4V, about 13.1V immediately after disconnecting the chargers.

However before I go out and buy the rest of the chargers I would appreciate any comments on this approach!

Thanks,

David


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acmotor
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Jaycar MB-3612 charger

Post by acmotor »

Image
No NO NO,
I'll pretend you didn't do that. Image

It is for equipment and human safety that the earth is connected to the mains / primary side of the charger.
It is illegal to remove a mains earth connection and would be immediately rejected by Road Transport as is does not comply with electrical standards. (if they realised)

What you need to do is examine the charger. I gather there has been a connection made between the negative output and mains ground ?
This connection you can cut, so as you say, the output is floating (isolated).
Personally, I am very suprised that the connection has been made and would question the manufacturer. Most modern supplies are isolated.

I use a system of 12 x 48V SMPS 2A battery chargers from China (via e-crazyman off ebay) These are isolated output and I have megger tested them to 500VDC. I also run 3A fuses on each line (+-) from the battery (module) to the charger (located at the battery).

Total current may be an issue with the 12 chargers.
14V x 12A = 168 W, allowing for efficiency and power factor this will be 1 to 2 amps at 240V. (check charger spec)
12 of these gives 12 to 24 A at the 240V mains end. Might be OK in a 15A outlet.
My system pulls nearly 10A but is only half the power chargers.

Turn on surge is another issue. Most SMPS have a turn on current of up to 30A as they charge their capacitor bank.
12 x 30 = 360A turn on surge !!
I turn my chargers on three at a time as I blew a mains fuse the first time with them all.










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antiscab
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Jaycar MB-3612 charger

Post by antiscab »

wow, i didnt realise the turn on surge lasted long enough to take out a mains fuse. i intend to use 6 of the same units you have (tuarn), i wonder if i can get away with plugging 6 in at the same time?
i spose ill find out the first time i try:p

Matt
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Jaycar MB-3612 charger

Post by antiscab »

hang on, y should it matter if the negative side is connected to the mains ground?
its the neutral you should be worried about.
If you have a short circuit problem because of the ground being connected to the negative side, this is the least of your worries.

Matt
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Post by acmotor »

???? are you trying to confuse me ????

The problem is when trying to charge a battery string of say 10 x 12V batteries with separate chargers, the charger's outputs must be floating, from mains earth and each other - obviously !

My original comment was that a battery charger's output should be floating in the first place, from the factory. You must not make it float by cutting the mains earth wire off !


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drowe67
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Jaycar MB-3612 charger

Post by drowe67 »

I just looked inside the charger, and traced the connections of the AC earth with a multimeter. There is no connection between the AC earth and the AC side of the power supply, except for a couple of capacitors used for Radio Frequency (RF) noise suppression.

The AC earth is connected to the case and negative output rail via a flying lead.

The low voltage side is isolated by two transformers, so the low voltage (DC) side is floating, apart from the earth connection.

So as per my original posting, I would guess the main purpose of the earth connection is to reduce RF noise, not safety. If this was essential for safety then all switch mode chargers would be grounded, whereas many don't use earth at all (e.g. your phone charger).

I have seem similar designs on other high-ish current switch mode power supplies, e.g. you can often find a direct connection between AC earth and DC negative on your laptop power supply (you can test this with a multimeter if u like).

As acmotor suggested, a good option is to break the earth connection inside the power supply (leaving the case grounded and the RF capacitors connected). At any rate breaking the earth connection appears to make the output float OK, at least on my two battery test.

Thanks for the tips on start up currents and total current - excellent points. I will try to measure these. Maybe some sort of soft start would help?

BTW if the total current is a problem these chargers have a 6A option via a switch and also a 6A version is available (about $20 cheaper).

Thanks,

David
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Post by commanda »

You can get these chargers cheaper from Soanarplus
https://www.soanarplus.com

Same part number.

Do not disconnect the mains earth.
DO disconnect the output negative from the earth. From memory, on the sister unit (24 volt 6 amp) it's a single green/yellow wire from the pcb to the chassis.

I've got a number of these now. A 12 volt 6 amp unit for general charging. Several years old now and has a noisy fan. A 12 volt 12 amp unit fitted to a push along fork lift at work. And 2 x 24 volt 6 amps for charging my EVT at work.

Edit: The case is grounded because it's a metal case. It's a safety issue.

Amanda
Last edited by commanda on Sun, 20 Jul 2008, 04:13, edited 1 time in total.
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Jaycar MB-3612 charger

Post by DVR »

drowe67 wrote: 4/ Using multiple chargers has one weakness - if a charger fails you can drive off with 11 full and 1 discharged battery, causing possible damage to that battery.


There are a few more downsides to consider.

1) 12 separate charger take up a huge amount of room and therefore are not easily carried on board.

2)And there is also the matter of the extra weight that 12 chargers adds to what is often an already overweight "lead sled".

3) If these cant be overcome and you leave your chargers at home then your range is limited to a radius of 1/2 your usable charge because you cant do opportunistic charging.

4) Often this method of charging is done because it is cheaper than a "proper" charger especially if cheap low end chargers are used. This can cause overly long charging times.

KIWIEV had this problem. He paid $708 for his chargers and a total of $265 for plugs to set it up so that alone cost him $973 but there is also a time factor to concider in the cost. It prooved UNSATISFACTORY as he could only go to 50% dod or he couldn't achieve a full charge overnight, and charging during the day was too slow to be worthwhile!!! He soon gave up on his 12 chargers and forked out the $1400 it cost him for his ZIVAN so thats $973 WASTED. KIWIEV only used 3.5 amp chargers and I dont know what spec the chargers you are looking at are but you better be sure that this method is actually going to work satisfactorily if it's cheap.


So long and thanks for all the fish.
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Jaycar MB-3612 charger

Post by antiscab »

sounds like kiwiev bought chargers that were under powered.
for the chargers being discussed here, overloading the single phase line will probably be more of a problem than the chargers not being powerful enough.

as far as space goes, this is vehicle dependant, though having seen the 12x15A chargers on the evshop conversion, this isnt usually a problem.
mounting the chargers off board and using a 32-pin plug is the expensive (and unreliable) way of doing things.

for me i know when a single charger fails as the floating voltage of the whole pack is lower than usual. This is usually my first warning, on my scooter i occasionally forget to reset the bms, so the booster pack charges, while my main pack doesnt. i can tell because the voltage when i get to the scooter the next morning is much less than the usual 70.7v. The situation should be similar for a car conversion.

Matt
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Jaycar MB-3612 charger

Post by drowe67 »

Amanda: Thanks for the tips and reports of long term usage of these chargers - yes I have found that wire inside.

DVR:

Re (1) I can fit the 12 chargers in OK in the rear of my Charade, but it will take a little time to build up a bracket and wire them up. Working on that now - will post a photo when complete.

They weigh 800g each so 10kg total, about 1% of my EVs mass. They can charge at up to 12A each, so charge time should be OK. Total cost was around $1k over the counter from Jaycar in Adelaide. I am a little concerned about overall reliability over several years, so I admit it's a bit of an experiment.

However even if one of the 12 chargers dies when I am 50km away from home, I can just substitute any old car charger. I imagine that a Zivan is more reliable but I bet if it died while in use here in Adelaide I would be without a charger for some time.

Is a Zivan NG3 AUD$1400 or was that USD? I thought the NG3 was around AUD$2k here.

The other reason I chose this approach is that it avoids the need for a separate BMS - each of my Yellow Top AGMs is charged separately. If I used a single charger such as Zivan I would need Rudman regulators or equivalent, at maybe an extra AUD$50x12 ($600). So even with a $1400 NG3 thats around $2,000. Maybe closer to $3k if the NG3 is AUD$2k delivered to Adelaide.

Matt:

Agreed on the loading of the single phase AC line - I will check that out. I will also be installing a Paktrkr to monitor each battery, this gadget can also instrument the pack (motor current and total pack voltage).

Cheers,

David
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Jaycar MB-3612 charger

Post by antiscab »

hi Dave,

Just one point re the paktrakr, it doesnt count AH, so isnt any good for determining soc (i didnt know this until i bought one), though it is exceptionally useful for data logging.

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Jaycar MB-3612 charger

Post by DVR »

drowe67 wrote:
Is a Zivan NG3 AUD$1400 or was that USD? I thought the NG3 was around AUD$2k here.


The Price of $1400 in in NZ dollars. GAV from KIWIEV.COM imported it from EV- America. Thats what it cost him including freight and taxes according to his site. Considering the KIWI dollar = only $0.76USD It's an EXELLENT price. The AUS dollar is $0.97

David Everything you said sounds good tho. I wasn't trying to say you made a mistake. I was just pointing out some of the other shortcomings/pitfalls that may not be known to other readers of this thread.


So long and thanks for all the fish.
drowe67
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Post by drowe67 »

As promised here is a picture of the chargers installed in the rear of the Charade. Actually this is 10 of them, I will fit two more in the front.

Image

It was quite a lot of work to build the brackets up, and I had to run 6 cables up to the front of the car. Two cables per charger are required (despite the series connections of the pack) so the charger current sensing works correctly.

If I had my time again I would probably lean towards a single Zivan type charger with Rudman regulators. This would cost more up front but would be less work to install and I could take the charger with me to the next pack (say Lithiums).

However for a low cost conversion, say a 6 battery 72V NEV, I think I would use this approach again, as you get good balanced charging for < $500.

I have removed the internal ground wire from all chargers so that all chargers float and this seems to be working OK. I have run out of power boards so haven't tried running all 12 chargers at once yet (maybe 9/12 running last night at one time). I want to test if the switch-on in-rush current of all 12 chargers at once pops any breakers.

The lights of all these chargers running are pretty at night.

Cheers,

David
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Post by Electrocycle »

I hope you got an Electus account for those! They'd be about $50 each then.

I use two of these chargers for my bike (a 12v one and a 24v one) and disconnected the ground wire from the case to the -ve battery connection.
The case is still earthed to the mains lead.
The charger specs said it was isolated, but when I first connected two up there was smoke :)
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