Experimental DIY Trickle Charger/Battery Maintainer + DIY Engine Service Lamp

Waiver:
Careful if trying this; this is an unregulated constant voltage trickle charger. If your battery smells like a bad egg it's about to explode.
If it starts boiling (bubbling noises) you're doing it wrong.
If you don't have a multi-meter don't attempt this.

I've put together this trickle charger entirely from salvage to keep the lawnmower battery alive over the Winter. I'll up-cycle it to maintain my leisure batteries when I retire them if I get it to work as per design. I'm still testing it at the moment.

My Aldi charger had a go and was having none of it, battery was 12.3v when I rescued it.

This was where it got to after a 5 second Aldi charger attempt.

It's a fairly simple idea all I need is a low current constant voltage source in the range of 300mA @ 13.4v and a timer.

Here's the best contender I could muster.

Output rated at 13v and 300mA

+ Timer (more on this later)

I tested the wall-wart to verify it was within it's spec.

:rolleyes:
4.6v Over-voltage and polarity reversed.

At this point I would recommend getting one within spec. but seeing as I don't have one let's carry on...



I stripped the socket off and marked the +ive with red tape...




...Wired battery clamps onto it, stuck it on the battery (overvoltage or not it's just a trickle charger) and checked the current.




Battery voltage on Trickle-charge
(this will rise as the battery gets charged)




The VRLA Battery eventually hit 14.4v after about 2 hours and I endeavoured to buck the float max with resistors I gleaned from an old cathode ray tube TV.
This is a resistance of 15Ω

After 3 hours it had risen to 14.1v so I'm currently testing 50Ω hoping it will level and hold at ~13.5v.
If it doesn't, no matter I can do the rest with the timer. Obviously this is a faulty transformer, Mk-2 shouldn't have need of buck resistors.

Meanwhile at the other end of the workshop I knocked this out...as needs must.

3W 12V MR16 LED bulb on battery clamps
(no fancy solder, switch or fuse:D)




Ta-Da!
Runs off engine battery!

holyhutzpa

And a sneaky glimpse at the "new" daily?
The wiring seems overkill for an LED lamp, but they look like they were jump leads in a previous life, and not very big for that purpose...

And I am intrigued by your new trickle charging solution - I presume you have to keep a close eye on the voltage?

(As already said by PaddyP I think -) You really should get into Arduino programming. They're really nice for measuring voltage and controlling variable voltage outputs...

That's my rubbish Halfords charger re-incarnated
Now that I've stripped half the main PCB off that charger I found the blown cap. that may have been the issue (€1.50 fix :rolleyes:).
The cable's handy because I can just shove the bulb pins straight into the strands, anything below 2.5mmØ cores is a bit difficult and needs a real bulb holder.

I'm only monitoring the trickle charger until I can stabilise it. You need to go 0.5v higher than the terminal voltage of the battery for it to start accepting charge. So 13.3v is the target but I can happily live with < 13.7v given weather etc. It's pretty difficult to "regulate" this with resistors because as soon as the battery voltage rises the output changes.
Then calculate the self-discharge rate (educated guess at the moment is 300mA) and regulate that with either a timer or fancy gubbins.

I've almost got it to stabilise at 13.4v with an impedance of ~90Ω. Once I do it's just a case of setting the timer to off-peak ESB rates.
If it doesn't ever stabilise I'm going to see how long it takes to rise to 13.6v then set the timer to that value daily.

It's very handy on a borderline battery that a regular charger just rejects.

The transformer I'm using is old school judging by the weight so I'm guessing it relies on the recommended device load for final regulation, I tried another one and it has a similar over-voltage issue.
I'd think a newer switch mode transformer would work without the resistors.

PaddyP closed his account.
We might have to petition his return for the sake of the lekytrons!

Arduino is on my shopping list after a car suspension renewal...so way down the line.

holyhutzpa

holyhutzpa wrote: »

And a sneaky glimpse at the "new" daily?

Nah that's a 3 cylinder 4x4 (originally 4 cylinder :rolleyes:) that runs on just about anything oil based. It's not mine.
My daily is stripped down and gradually getting greener while I source 2 x A4 pages of parts :pac:.

holyhutzpa

Ahh I see now. Looks like a Daihatsu? They're great 4x4s but you have to regularly waxoyl them (or at least, a friend's one rotted after a winter of neglect)

We have to get PaddyP back. I'm hoping to do a few projects with a Raspberry Pi and also Arduino in the van...


Using an arduino, you should be able to (theoretically), regulate the voltage?
you would have a maximum input of (say) 14V, going through a digital pot
The arduino could measure what's happening at the battery, and depending on what voltage it sees it can control the percentage output of the digital pot?
Arduinos can measure voltage really easily - they have a analog voltage in pin...

I'm hoping to use the analog in pin, with strip of resistors to measure water level (and approximate volume) in the campervan by shorting out the input current at the top of the water, and measuring the voltage when it comes back.
I think it will be a while before I build up to frankenmonster tasks like DIY trickle chargers :P

moodrater

holyhutzpa wrote: »

Ahh I see now. Looks like a Daihatsu? They're great 4x4s but you have to regularly waxoyl them (or at least, a friend's one rotted after a winter of neglect)

We have to get PaddyP back. I'm hoping to do a few projects with a Raspberry Pi and also Arduino in the van...


Using an arduino, you should be able to (theoretically), regulate the voltage?
you would have a maximum input of (say) 14V, going through a digital pot
The arduino could measure what's happening at the battery, and depending on what voltage it sees it can control the percentage output of the digital pot?
Arduinos can measure voltage really easily - they have a analog voltage in pin...

I'm hoping to use the analog in pin, with strip of resistors to measure water level (and approximate volume) in the campervan by shorting out the input current at the top of the water, and measuring the voltage when it comes back.
I think it will be a while before I build up to frankenmonster tasks like DIY trickle chargers :P

Problem with measuring the level is fitting and sealing the assembly and corrosion, resistive deposits aka scum in waste tank. Modern washing machine use a tube and pressure sensor like these zanussi/aeg/electrolux ones output is a freuqency proportional to the pressure. I have one in my junk box, oh to be young and single and have time for projects like this again

http://www.ebay.co.uk/itm/Zanussi-ZWF14070w-Water-Level-Pressure-Switch-Washing-Machine-Spares-Genuine-/111233338596?pt=UK_Irons_Presses&hash=item19e6060ce4

http://www.ebay.co.uk/itm/Zanussi-Aeg-Electrolux-washing-machine-pressure-sensor-132516202-/271367868247?pt=UK_Irons_Presses&hash=item3f2ec90f57

holyhutzpa

Ahhhh, that's interesting. I thought about a pressure sensor, but this is actually "clean" water, so I reckoned I'd get away with it...

I've also got more ideas than I have time for, but I am starting to prioritise fun electronic ones.

holyhutzpa

holyhutzpa wrote: »

Ahh I see now. Looks like a Daihatsu? They're great 4x4s but you have to regularly waxoyl them (or at least, a friend's one rotted after a winter of neglect)

Well spotted. She had a complete remantle and re-spray 3 years ago with a Lidl air compressor after roller brush attempts had failed.
I Waxoyled the interior of my van under the ply and it's done wonders for condensation repression. Wouldn't let it near a chassis though given that I'm the one who services it. Manky stuff, never dries. I go with stone chip.

For the tank sensors I'd try to avoid permanent loads on the batteries wherever possible. So I'd want a switch activated readout rather than one constantly displaying. My tanks are small and easy to eyeball though.
H²O is an insulator, you'll be relying on fluoride, trace minerals and impurities in your "clean" water to conduct, I've thought about linear resistive float sensors before but don't think I need one really.

I've been fiddling with Mk-2 trickle charger using fixed regulators but the lowered voltage doesn't seem to be able to defeat the battery's internal resistance. I kinda want to keep it as simple as possible, adding too many gizmos tends to make it an inaccessible endeavour to most DIYers.
This is the simplest regulated version I could find. I think most people have a timer lying around sooner than a bag of capacitors and resistors.

Probably all I'm offering here is a cost effective imperfect solution.
It's quite often cheaper buy these things than make them unless you horde junk.
If anyone has better success with a switch mode traffo. let us know?

There's a certain paradoxical mentality that I'm out to buy a very expensive 125w (gas equivalent) soldering iron to cut through all this Rohs lead-free solder on boards these days rather than go down to an electronics shop and pay buttons for proper components. :rolleyes: I ought to be petitioning the government for my WEEE money back too.

Having said that I'd love to see how you get on with the Arduino and Raspberry Pi when you get around to it.

Float charger Mk-2 didn't prototype very well. It consisted of the transformer with a 9v regulator referencing a 5v regulator (didn't have a 13v reg. in the bone yard), I added a diode too and didn't bother with the capacitors because if it required refinement I'd do it later and in the meanwhile it could be a de-sulphater too.
It was outputing about 14.5v open circuit. It took two days to get the teeny VRLA from 12.8v to 13.1v at which point I scrapped it. I'd run out of patience and thought it was a waste of lecky. If I wanted a permanent float charger I'd prefer build the one I linked to earlier because that's current & voltage regulated.

That left me back to the MK-1 timer idea.

From the bare end that's;

• 50Ω resistor + 30Ω in series= 80Ω; this slows down the charge and limits the voltage max. Resistors dissipate surplus volts as heat so that's why the larger is first, they have a heat rating in watts when you buy them but you can tell by size and touch if in doubt....and smell too sometimes

• 1amp diode with heak sink; protects traffo from battery, prevents battery discharging running the traffo backwards (up to the bridge rectification). Also adds a smidge of voltage drop (this one is 0.3v drop open circuit)

• Croc clip.

+1 DIY fuse holder



1 amp fast blow...smallest I could find with a legible rating.


Insulated Assembly

You can calculate what you need as a charge time by getting your manufacturer's recommended trickle charger spec. (eg. 1/20th the C20 rating) compensate for temperature and self-discharge etc.
Why bother though... It takes my trickle charger 2 hours to hit 13.8v from 12.8v. I'm seeing a float charge of 14.0v on a 13.6v set-point on the van batteries given weather so I reckon 13.8v is fine with law of averages.

Please do not try this on dead batteries, that would be dangerous (terminal voltage less than 10.5v).
Weak, borderline or healthy and just unused it'll work fine, just not so well as a real float charger.
When you think about it it's the same thing as an over-priced unregulated 15watt(ish) solar panel except from mains.

Sir Liamalot

Sir Liamalot wrote: »

...I've thought about linear resistive float sensors...

Some fuel tank sender units use these. The fuel gauge is just an analogue voltmeter.
I've no idea if modern cars still use this system, I don't work on computer controlled automobiles.