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New solid state Car battery CHARGERS are irritating.

gary350

Well-Known Member
55 years ago car battery charger was a transformer & rectifier that produced 18 volts DC. from 120 VAC.

Now year 2021 car battery charger can not be used to power a 12 volt car head light. It can not be used to test 12 volt electric brakes on an RV. New battery charger won't work unless it is connected to a good working car battery. Is there any way to make these new chargers put out a voltage with no car battery???
 
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Diver300

Well-Known Member
Most Helpful Member
The battery chargers of 55 years ago couldn't be left on a battery for too long or the battery would be damaged. They would blow a fuse, at best, if the terminals were reversed.

Something like this:- https://www.ebay.co.uk/itm/MINI-FRI...S-12V-VOLT-POWER-SUPPLY-ADAPTOR-/190882903153 will run a headlight bulb or a couple of RV brakes.

Of course, modern headlights may need the correct CAN or LIN signals to light up.
 

Externet

Well-Known Member
I suspect some geniuses pulled too many 5+ year abandoned cadaver batteries from two feet deep backyard weeds and tried to recharge them with a battery charger getting an open circuit in them and no action from the charger; or a short circuit in them and smoke out of the charger.
Warranty claims for 'non working' new chargers due to users ignorance (to say it politely) rose so much as anyone that thought they could just connect it and solve a dead battery problem, that the industry decided to design a charger that would refuse to recharge a dead, shorted or overdischarged car battery and that is what we have now in the market.

To not be irritated, it is necessary to measure the candidate battery voltage and read the manual of the charger to know its inner workings and limitations and disabling mechanisms.
I suppose that a modern charger brought back to the store by claiming warranty, can be demonstrated as functional when tested with a proper battery, and prove the incompetence of the claimant.
To put headlight bulbs to work, a 12V power supply is needed instead of a battery charger, and everything will work rosy... It is a battery charger, not a bulb lighter.

The chargers manufacturers solved their warranty problem; but they will not educate the public. It is not their task.:oops:
 

JimB

Super Moderator
Most Helpful Member
Deja Vu is a French expression which can be loosely translated as "we have seen all this lot before".

With that in mind, the forum software is showing Similar Threads just below this one, and top of the list is this one from 2018 ....


Funny old world.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
55 years ago car battery charger was a transformer & rectifier that produced 18 volts DC. from 120 VAC.

Now year 2021 car battery charger can not be used to power a 12 volt car head light. It can not be used to test 12 volt electric brakes on an RV. New battery charger won't work unless it is connected to a good working car battery. Is there any way to make these new chargers put out a voltage with no car battery???
You're looking for a power supply, not a charger - luckily those old crappy chargers are long gone.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Deja Vu is a French expression which can be loosely translated as "we have seen all this lot before".

With that in mind, the forum software is showing Similar Threads just below this one, and top of the list is this one from 2018 ....


Funny old world.

JimB
Were I used to work we used to sell TV's, including some that were 12V capable - almost all of them came back with complaints they didn't work on 12V. In almost every case (all except one) they were trying to run the TV from an old battery, that they had taken off the car because it wouldn't start it.

The single 'other case' was a millionaire with a brand new luxury caravan, and that was simply that the wiring in his EXPENSIVE caravan was too long and too thin. I measure the resistance from battery terminal to 12V sockets inside, under load, and it was in multiple ohms both sides.
 

gary350

Well-Known Member
I need a 12 volt DC power supply to test the electric brakes on an old camper trailer that I am restoring. I can not remove a battery from a vehicle that makes computer loose memory and radio no long works until the code is entered. Maybe I could solder 50 ft of #14 romex house wire to jumper cables so I can use car battery to test brakes in the work shop. It will be easier to build a 12 vdc power supply it will be easy to connect to brakes. I dug through most of my stuff and found a 200 watt 12 vac transformer. I have no clue how much power it takes to make 1963 electric brakes work? Old brakes might even be 6 vdc if so they need to be wired in series. Nice thing about old trailer no one every puts many miles on then like cars brake shoes look barely used with 60 years of dust.

006.JPG
 
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ChrisP58

Well-Known Member
Most Helpful Member
I do not recommend wiring two brakes in series.

Since the current for one has to flow through the other, then any opening or loose connection in the wiring will cause both brakes to fail.
 

Diver300

Well-Known Member
Most Helpful Member
12 V brakes take around 2.5 A per wheel, so they are around 5 Ohms. 6 V ones would probably be about 1 - 2 Ohms.

You could wire 6 V brake magnets in series. There are plenty of other places where a single broken wire would stop the trailer brakes working, so I don't think that putting two brakes in series increases the risk significantly. With a modern brake controller you will get an immediate indication that the brakes are open circuit, even if you are not using them at the time.

A modern brake controller is adjustable, so you could just wire up the 6 V magnets in parallel. It will probably work fine, and the adjustment will be in the bottom half of the range. If you find that the brake adjustment is too sensitive, you could just change to 12 V magnets or put a 2 Ohm resistor in series with each brake. You will need to use a resistors rated to 100 W or more.

You could buy a rectifier for the 12 V transformer. Something like this would be fine:- https://www.ebay.com/itm/224241646030

You will get more than 12 V out, but to test the brakes it would do. It will take ages to overheat the brake magnets.

I found out recently that proportional brake controllers existed in the 1950s. They had a connection to the brake hydraulics so that the voltage to the brakes tracked the brake pressure.
 

gary350

Well-Known Member
12 V brakes take around 2.5 A per wheel, so they are around 5 Ohms. 6 V ones would probably be about 1 - 2 Ohms.

You could wire 6 V brake magnets in series. There are plenty of other places where a single broken wire would stop the trailer brakes working, so I don't think that putting two brakes in series increases the risk significantly. With a modern brake controller you will get an immediate indication that the brakes are open circuit, even if you are not using them at the time.

A modern brake controller is adjustable, so you could just wire up the 6 V magnets in parallel. It will probably work fine, and the adjustment will be in the bottom half of the range. If you find that the brake adjustment is too sensitive, you could just change to 12 V magnets or put a 2 Ohm resistor in series with each brake. You will need to use a resistors rated to 100 W or more.

You could buy a rectifier for the 12 V transformer. Something like this would be fine:- https://www.ebay.com/itm/224241646030

You will get more than 12 V out, but to test the brakes it would do. It will take ages to overheat the brake magnets.

I found out recently that proportional brake controllers existed in the 1950s. They had a connection to the brake hydraulics so that the voltage to the brakes tracked the brake pressure.
We go camping with 6 different vintage camper trailer groups there are usually 45 to 90 vintage campers at each 3 day weekend event. Any time someone is have a brake controller that is very sensitives it is because they have 6v brakes connected in parallel to a 12v controller. With 100 people at an event there are usually someone that has tools, connectors, wire, so we can rewire their 6v parallel wired brakes in series then the 12v controller is less sensitive. When people rebuild bad brakes they buy a 12v brake kit. Camper groups are a good source of information. If brakes are wired in parallel and you loose brake on 1 wheel it can wreck the tow vehicle if you suddenly need to stop 1 wheel will grab and pull the vehicle off the highway on the right or into left lane into on coming traffic. Make sure wires are tied up if you run over something that breaks 1 parallel wire then you have only 1 wheel with brakes and won't know it until you need to stop. It is much safer to have electric brakes wired in series but you won't find factory wired brakes in series. My first brake controller gave me numbers 1 to 25. The new brake controller gives me numbers 1 to 12 this is battery voltage to the brakes. We have another camper trailer I have controller set at 6.8v this is perfect brakes for this camper trailer. Wife & I are tired of climbing over each other at 3pm to get out of bed to pee so the next camper trailer bed will be rotated 90° so we can get out on both sides.

I have a 25a bridge rectifier I can use on the 12v transformer all I need to do is spin wheel by hand then turn on 12v to see if wheel locks up while setting up on cement blocks. As long as both brakes have the same stopping power it will work. After trailer is built then I can test brake with tow vehicle battery & controller.

I wish I could use a 12v battery charger to test my electric brakes so I don't have to build something.
 
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unclejed613

Well-Known Member
Most Helpful Member
what i use for most 12V use, including battery charging, are industrial open-frame power supplies. they're usually found cheap from surplus electronic dealers, and for instance the three i have use foldback current limiting (adjustable current threshold), which works great for charging lead-acid batteries properly. they also have sense wires, and if the voltage adjustment doesn't go quite high enough (these would adjust to 13.2, but you need 13.8 or 14.4 for properly charging modern batteries), you can add a couple of diodes between the sense terminals and the output terminals to boost the voltage.
 

gary350

Well-Known Member
what i use for most 12V use, including battery charging, are industrial open-frame power supplies. they're usually found cheap from surplus electronic dealers, and for instance the three i have use foldback current limiting (adjustable current threshold), which works great for charging lead-acid batteries properly. they also have sense wires, and if the voltage adjustment doesn't go quite high enough (these would adjust to 13.2, but you need 13.8 or 14.4 for properly charging modern batteries), you can add a couple of diodes between the sense terminals and the output terminals to boost the voltage.
That would be great if I had one. I have a book that says, voltage must exceed 1/2v for each cell for a lead acid batter to charge. Car batteries have 6 cells, 6 x 1/2 = 3volts. 13.2v + 3v = 16.2v Charger needs to be about 17v.

But I am not using a battery charger to charge a battery I need to test 12v electric RV brakes. MY new technology battery charge puts out NO voltage when connected to electric brakes. Touch + & - wires together no sparks. The circuit needs a voltage from the battery to know it is connected to a better before it will produce 12 volts.

We are leaving town for a few days when I get time I will take the new battery charge apart it probably has a 12v transformer, if it does I can solder a bridge rectifier to the transformer to get 12v x 1.414 =16.968 volts. I can drill holes in the metal case and add 2 terminals for 17 vdc. Electric brakes are 12v and 17v for 3 second test won't be a problem for the brakes. It might be better for me to put a selector switch on the output wires of the battery charger so I can switch + & - wires to the 17v from bridge rectifier.
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
You should find that a 9V battery plus a series diode to prevent it being charged will enable the output.

I've used that arrangement to get one to give an output on a dead battery, for a friend.
The charger worked but the battery was beyond hope.
 

shortbus=

Well-Known Member
Most Helpful Member
I will take the new battery charge apart it probably has a 12v transformer, if it does I can solder a bridge rectifier to the transformer to get 12v
I'm betting it won't have that. If this type of thing is an ongoing interest why not just spend a few bucks? Or go to a pawn shop or secondhand store and get an old charger? Or do what Diver said in post #10?
 

Diver300

Well-Known Member
Most Helpful Member
I'm betting it won't have that. If this type of thing is an ongoing interest why not just spend a few bucks? Or go to a pawn shop or secondhand store and get an old charger? Or do what Diver said in post #10?
I would agree. Any 12 V, 5 A charger that weighs under 2 kg (5lbs) won't have a mains frequency transformer.

I have seen some modern battery chargers which have a supply mode, so they will just turn on and provide 14 V or so. However, if yours doesn't, retrofitting it would be a pain.
 

gary350

Well-Known Member
You should find that a 9V battery plus a series diode to prevent it being charged will enable the output.

I've used that arrangement to get one to give an output on a dead battery, for a friend.
The charger worked but the battery was beyond hope.
9v battery & 1N4007 diode sounds easy I will try that first.
 

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