professor95 wrote:
When I referenced a brute force transformer battery charger having a better power factor than a modern switching charger I was thinking about this thing. It is about $100 to $125 and will quickly recharge a battery bank at 40 amps from the 2000i no sweat. But, as I noted it is NOT a "smart" charger and can overcharge a battery if left on 40 amps unattended - which is why it includes a built in timer. Charge rate can be switched to 15 or 2 amps as well.
I have that very charger and far from 'smart', it is a seriously stupid charger.
I was baffled at why it didn't put a full charge on my Optima AGM battery on its 2 amp setting until I put a voltmeter across and found it was going to a maximum 12.2 volts on that setting! Since a full charge is 12.65 volts after the battery has had time to settle after coming off the charge I understood that a guy could leave it on that setting all day, it isn't going to put more than half a charge on the battery. The '15 amp' setting was near full charge voltage but that meant that as the battery approached full potential the charge rate would slow to next to nothing.
So I put it on the 40 amp setting and found the voltage was now dangerously high, over 15.7 volts. That's when I came up with the brainwave to put an old car headlight in series with the charging battery, to reduce the voltage by adding resistive load.
It worked well, or seemed to. It charged at just under 14 volts, a comfortable charge condition similar to what the battery experiences in the vehicle. It seemed stable, so I left it like that for a while. When I returned however, I ran smack into the educational reality that a charging battery presents a varying load as it achieves a greater state of charge, and it was now sitting at a high voltage again despite the in-series headlight. The battery was hot to the touch, and ruined.
Pretty certain that the Professor will have a far better way of explaining it but what I believe I found is that advertized 'amps' is a common and expected but unfortunately misleading way for a maker to indicate what rate a charger is charging a battery.
The actual amperage flowing is going to be dependent on a number of factors such as the batteries present state of charge, the physical size and capacity of the battery, the line voltage supplying the charger, and the soundness of the contact of the clamps. A '2 amp' charger hooked to a big old Cat battery 'might' be charging at a rate of 2 amps but hooked to a little motorcycle battery, be pouring a whole lot more into it.
For the battery charger maker to claim how many amps their device is going to be charging your battery, is like an engine maker blindly providing a throttle setting at the factory and then telling you how fast that's supposed to make your vehicle go, without them knowing how heavy the vehicle will be, what gear it will be in, or how level the road will be!
Sort of...
In any case I'm sold on voltage controlled smart chargers. :) Best thing since low ash oil.
