converting an auto battery charger to manual

[stonefly]

Can I convert an automatic battery charger to manual?

The old manual chargers work much better for my purposes. I don't want a charger putting itself into "float" mode or otherwise reducing amps to the battery. I want to be the one who decides when the battery has had enough. This is impossible with today's modern automatic chargers. There must be a way to bypass or shut off the automatic circuits. Does anybody here know how to do that?

As far as I know, it is now impossible to buy a truly manual battery charger. I have one, an old Schumacher, about 20 years old. I love it. I want another one, but I realize I must make it myself.

 

[NutBucket]

n /m

 

[sdifox]

Just buy a transformer of sufficient size and wire it up.

 

[stonefly]

n /m

?

 

[stonefly]

Just buy a transformer of sufficient size and wire it up.

Thanks, but that doesn't give me much to go on.

I already have several automatic chargers, and they already have transformers, and rectifiers. In fact, they have everything I need. Unfortunately, they also have some things I don't want. I'm hoping to find out that there is a simple way to open those things up and cut a wire or two in order to simplify the automatic function out of existence.

 

[sdifox]

Thanks, but that doesn't give me much to go on.

I already have several automatic chargers, and they already have transformers, and rectifiers. In fact, they have everything I need. Unfortunately, they also have some things I don't want. I'm hoping to find out that there is a simple way to open those things up and cut a wire or two in order to simplify the automatic function out of existence.

Just bypass the electronics, wire the output from the transformer directly to the charging leads.

 

[stonefly]

Just bypass the electronics, wire the output from the transformer directly to the charging leads.

thanks

 

[NutBucket]

My guess would be they have a switching power supply so I doubt it would be as simple as bypassing the electronics. It probably reads charge current and adjusts voltage output accordingly.

Sent from my Pixel 3 using Tapatalk

 

[RLGL]

I want to be the one who decides when the battery has had enough.

So the OP knows more that the engineers who work with batteries. Riiiiight!

 

[NutBucket]

The only time I believe a manual charger is advantageous is when you're trying to "bump" a battery with voltage so low an automatic charger will deem it defective.

 

[mindless1]

We would need more to go on, for you to open the patient and dissect it. I'm pretty good at reverse engineering circuits and modding them, but i have to know what the circuit is to do that.

If it switches to trickle mode it probably is a switchmode PSU. If it's just an old school transformer you do not just hook the charging leads up to its output, you hook them up after the diode(s) so it's DC instead of AC.

 

[mindless1]

Thanks, but that doesn't give me much to go on.

I already have several automatic chargers, and they already have transformers, and rectifiers. In fact, they have everything I need.

Do you have one with a large, heavy transformer, linear unregulated instead of regulated switchmode? If so you can use that, or if not, pick your target current and buy a 12V transformer.

Wire the transformer to a bridge rectifier of suitable current rating, or 4 discrete schottky diodes (as the bridge rectifier) would be less lossy and not need as large a heatsink (heatsink them), then add about 470uF capacitance for each amp current (arguable, for a lead acid battery charger you don't really need that much). A fuse would be nice to have too.

It is a very basic circuit, but without full charge current termination, if you leave the battery hooked up past full charge it will start to boil away the electrolyte (not really boil, rather electrolysis, convert the water to oxygen and hydrogen).

Example transformer:

12 VAC 100VA Power Transformer 8.333Amp

HEC P/N: HEC-5111C Input: 120VAC 60Hz Output: 13.5VAC NL ~12VAC @ 8.333A Specifications/Features: General use, Chassis mount transformer with 9inch wire leads for connections.

www.mpja.com

As far as I know, it is now impossible to buy a truly manual battery charger. I have one, an old Schumacher, about 20 years old. I love it. I want another one, but I realize I must make it myself.

Used charger from Craigslist, garage sales, ebay, etc.

 

[Paperdoc]

Do NOT just hook the transformer output to your battery!! A transformer only works on AC, and it is there just to convert the household 120 VAC into a battery's 12 VAC. BUT it does not supply exactly 12 VAC either. AFTER the battery there is a rectifier system - often a bridge of 4 diodes in a heatsink - to convert to DC with significant ripple, then at least one capacitor to damp out some of that ripple. Some MAY have a small inductor as part of the ripple filter system, but car batteries are not really fussy about that. All of those BASIC items cause a small loss of voltage. Then realize that the car battery really is NOT 12 Volt - it usually reads about 13.2 V with no load on it. So overall the entire unit is designed for all those factors. THEN on the modern ones there come the Voltage Regulator systems that adjust the actual voltage applied to the battery to charge it rapidly when it needs that, and to keep only a small trickle charge current going when it is fully charged. It is those last things you want to avoid. But you really would need to understand the entire circuit in a modern charger to know how to change its design to your wants. Just bypassing selected components is likely to get you trouble.

 

[stonefly]

Do you have one with a large, heavy transformer, linear unregulated instead of regulated switchmode? If so you can use that, or if not, pick your target current and buy a 12V transformer.

Wire the transformer to a bridge rectifier of suitable current rating, or 4 discrete schottky diodes (as the bridge rectifier) would be less lossy and not need as large a heatsink (heatsink them), then add about 470uF capacitance for each amp current (arguable, for a lead acid battery charger you don't really need that much). A fuse would be nice to have too.

It is a very basic circuit, but without full charge current termination, if you leave the battery hooked up past full charge it will start to boil away the electrolyte (not really boil, rather electrolysis, convert the water to oxygen and hydrogen).

Example transformer:

12 VAC 100VA Power Transformer 8.333Amp

HEC P/N: HEC-5111C Input: 120VAC 60Hz Output: 13.5VAC NL ~12VAC @ 8.333A Specifications/Features: General use, Chassis mount transformer with 9inch wire leads for connections.

www.mpja.com

View attachment 45858



Used charger from Craigslist, garage sales, ebay, etc.

This is very helpful.

Thanks.

 

[stonefly]

So the OP knows more that the engineers who work with batteries. Riiiiight!

I have a voltmeter that is always on and visible. When the battery voltage goes beyond 14.2 volts, I switch my Schumacher se-4020 from 40 amp charge to 10 amp charge. When the Schumacher is set to 10 amps, the voltage stays around 13.6 or 13.7. The old Schumacher has no circuitry that reduces the charging current. I can use that battery while it's charging and not worry about a thing.

The Schumacher fully charges charges the battery.

Perhaps you've never driven a big truck. The alternators on big trucks charge the batteries to 14 volts. Automatic battery chargers on the market today charge batteries to 12.6 volts—and then reduce the charge rate. You'll never get a battery up to 14 volts if you reduce the charge rate as soon as the battery reaches 12.6 volts.

 

[stonefly]

The only time I believe a manual charger is advantageous is when you're trying to "bump" a battery with voltage so low an automatic charger will deem it defective.

I'm using the batteries for an inverter, to supply 120 volts AC. Automatic chargers are fine if you only need to charge a battery enough to start a car, but if you need to get your batteries to as high a charge level as possible, in order to provide a steady, low current to an inverter, you'll need more than an automatic charger, which reduces the charge rate as soon as the batteries hit 12.6 volts.

 

[mindless1]

I have a voltmeter that is always on and visible. When the battery voltage goes beyond 14.2 volts, I switch my Schumacher se-4020 from 40 amp charge to 10 amp charge. When the Schumacher is set to 10 amps, the voltage stays around 13.6 or 13.7. The old Schumacher has no circuitry that reduces the charging current. I can use that battery while it's charging and not worry about a thing.

The Schumacher fully charges charges the battery.

Perhaps you've never driven a big truck. The alternators on big trucks charge the batteries to 14 volts. Automatic battery chargers on the market today charge batteries to 12.6 volts—and then reduce the charge rate. You'll never get a battery up to 14 volts if you reduce the charge rate as soon as the battery reaches 12.6 volts.

You don't really need to get the battery up to 14V, in vehicles that is just a target to charge faster, while the battery full charge voltage is 12.6V then "slightly" more to top it off aka trickle or float mode.

If you had a charger that only does 12.6V it will fully charge the battery but as it gets closer and closer to this full charge voltage, it takes longer and longer to reach it due to the decreasing voltage difference vs battery impedance. It requires a voltage difference to put current through the resistance of the (battery) circuit. Typical float charge voltage is closer to 13V but even that will diminish electrolyte in the long term.

 

[RLGL]

I have a voltmeter that is always on and visible. When the battery voltage goes beyond 14.2 volts, I switch my Schumacher se-4020 from 40 amp charge to 10 amp charge. When the Schumacher is set to 10 amps, the voltage stays around 13.6 or 13.7. The old Schumacher has no circuitry that reduces the charging current. I can use that battery while it's charging and not worry about a thing.

Man, you sure fell into a deep rabbit hole!