Smart Battery Chargers

RJH formulated the question :

When stuck, one way is to put a second charged battery across the flat one, to get the charge to start, but its not a good idea to allow batteries to get that low.

I have a homemade 60amp smart pulse charger I built a couple of decades ago. It is capable of getting enough charge in a flat battery, in just a few minutes. Like the Aldi/Lidl ones, it would not begin to charge a completely flat battery, it had to see more than 10v of the correct polarity. I later added a button to enable me to force start the charge. I find I never need it now, with the Aldi/Lidl chargers around.

I leave them connected and never any problem with Aldi/Lidl type of charger. In my garage, by the drivers door, I have one such charger fixed. Every month or so, I take the lead (cigar lighter plug on the end) into the cabin and plug it into the cigar lighter socket and leave it charging for a couple of days.

In the distant past, using my home built/designed 60amp charger, I would disconnect the battery from the car - rather than risk damage to the ECU or other electronics.

I have one of each of the smaller OptiMate range of 12V smart chargers and found them all to be excellent.

I don't need to charge 6V batteries and as the smaller models only put out 0.8-1A, can be used on fairly small (motorcycle) batteries quite safely, up to bigger batteries as long as you are in no rush. Even the OptiMate 2 charges my 60Ah gel semi traction battery reliably. I also have one that does 5A for the bigger bike / traction batteries.

And with no buttons to press, if someone else in the house switches it off by mistake (and back on again) or a clip get's knocked off and put back on, it just starts up again.

It doesn't care if a battery is flat / sulphated as they have a de-sulphation / recovery startup mode (so will start the recovery process, even if they can't do any good and will time out if they don't see reasonable progress after a certain time).

Unlike other smart chargers (and typically the things you get with mobility scooters), I've not had an OptiMate carry on the bulk charge and / or drop back to maintenance / fail, when the battery is bad and would probably be heating up.

Not cheap but seem pretty good / reliable and appear to treat a whole range of LA batteries correctly (I often monitor / log battery charge / discharge characteristics).

I've never had a CTEK but I do have several with the push button and don't generally use them because of it (I've bought them because they seem too good to miss but then given them away to friends / family that have asked to 'borrow' a charger). ;-)

Cheers, T i m

It must have been an older design, your battery was U/S or you lost power for months as I've just tested it on my Optimate 4 and 5 (the 2 is round my Mums) and the background / discharge current on both was around 135uA?

Cheers, T i m

T i m explained on 04/10/2018 :

It was the Optimate which wrecked batteries, if mains power was lost for any length of time - without power it would actually discharge the charge from the battery and wreck the battery. Unless the have changed the design? Disconnect from the mains and the LED's would remain lit, powered from the battery, so obviously discharging the battery.

I was not at all convinced by any of that sales blurb from Optimate. I tested mine extensively on my bench with meters and scopes, I saw no such behaviour, just a steady 13.8v continuous output voltage whilst ever connected to the mains, inhibited when reverse connected (I Think).

Likely it was an early one, it was around 10 - 15 years ago and I complained bitterly to Optimate about how easy it was to wreck a battery. I kept the bike over winter in a shed at the back of the garden, shed fed from the garage which had its own RCD on the mains. If the RCD happened to trip for some reason in the garage, the shed could be without power for days, until I noticed. By then, it would need a new expensive battery. I seem to remember it cost me a few batteries at the time.

No, of course - I'd left an OBD scanner connected for a week or so accidentally. As it happened, the battery recovered and remained fine for 6 months, until i sold the car.

Snag for me would be getting a mains lead connected as the car's street parked.

Could be an old design then.

And that's not fun, especially when they are nearly new? ;-(

Mains power relay in series with the charger output. Auto start, no self discharge. ;-)

Not nice.

Hmm, fool me once ... ? ;-)

I have (built) a charge output switcher that can distribute a single (expensive) charger around 4 batteries (sequentially over an 'n' time interval).

Any of the chargers that need a push button to start would be no good for that, nor would where you leave the charger on (say indoors) and connect or disconnect the bike / car outside on the LT side.

Cheers, T i m

T i m pretended :

...and it only fooled me once, but at the far end of the back garden where it is impossible to keep a regular eye on it in winter - as in it would need to be checked every few hours.

They were sold as fit and forget battery maintainers, for the winter.

Same here. I have an outside socket, and lay rubber matting over the mains lead where it crosses the pavement.

I would have thought that a low-power light, visible from the house, would have shown if the shed power was off? The cost would have been worth it.

or a fairly hefty diode in one lead would sort the problem, or just get a ctek.

MrCheerful submitted this idea :

No - a diode would drop the delivered voltage by 0.7v and I suspect that original Optimate, not seeing a correct voltage from the battery, might assume reversed connections and not output.

anything over 10v the right way round would allow it to work

I'm not sure about that last bit?

If the charger had to 'see' a voltage from the battery before it would enable any output then it wouldn't see any back though a diode and so never start. If it was to output a voltage first then that would work but it would just do everything .7 of a volt lower (like cut off at

The OptiMate 5 only needs to see 2V before it start charging as I'm not sure how it might try to de-sulphate / recover a 'dead' battery otherwise?

Monitoring such a battery on charge (Optimate 5) the voltage is pulsed up to 20 or so and you can only do that on a battery with a high internal resistance (generally equals 'nearly dead').

Cheers, T i m

there must be a simple external way that it could be made not to take a current if mains is off. I have a large 'Ring' smart charger that if the power goes off it flattens the battery in a few days, I found that one out the hard, expensive way :) yet the ctek has no offline draw and restarts itself. while the ring restarts (if the battery still has voltage)

MrCheerful used his keyboard to write :

There is....

A mains powered relay (contacts only make when it has a mains supply), with its contacts wired in series with the 12v output.