The charger is designed to charge a bank of large, lead-acid batteries. The batteries are in parallel and have a float voltage of around 36 V.
I understand the purpose of T2, L2, D1, and D2 - it's a simple full-wave rectifier. But what is the purpose of T1, C1, and L1?? Why are they doing that? Any ideas?
I think that might be a passive buck-boost transformer arrangement. Purpose is to keep the the charging voltage constant as the ac input voltage varies within a certain range . The capacitor and inductor form some kind of tank circuit I guess.
The voltage of T2 secondary is probably too to make 36V out. The voltage of T1 secondaries is added to T2 secondary. That probably makes the output voltage to high. L1 and C1 shift the phases feeding T1 secondaries, so when added to T2 the output is lowered to correct voltage.
This increases the number of voltage peaks from 120 per second to 360 per second (lower peak current, but faster average charging current because there are more pulses). Also, some power factor correction is achieved. These are likely the reasons for the complicated design (instead of using a different T2 alone).
This looks like a regulated supply using a constant voltage transformer. Capacitor C1 and the inductance of transformer T1 are probably resonant close to the supply frequency. Transformer T1 probably has a saturating core, which tends to change the tuning of the tuned circuit as the input voltage changes. This will change the output voltage in such a fashion that the input voltage variations are compensated. The input inductor L1 might be to improve the waveform coming out of the transformer, and transformer T2 might be a further compensation for voltage changes.
Sola specialized in this type of transformer. Later versions used a single transformer with a rather elaborate core that had saturating and non-saturating sections with and output winding with sections on various parts of the core.
These tended to be bulkier and heavier than a standard transformer, but they could provide an output at high power regulated within a few percent from a source that varied plus or minus 20 percent or more.
I have to agree with rshayes here for several reasons...
For one, i dont see any other means of regulating the output voltage,
and this would be a big requirement for a battery charger, and a
'constant voltage' transformer would certainly fit the bill.
Secondly, these transformers are known to be used in high powered
power supplies, like heavy duty battery chargers.
These transformers, often better known as "ferroresonant" transformers,
have the ability to regulate the voltage to some degree, but are highly
sensitive to changes in line frequency. On the up side, they are very
reliable because there are no switching elements (like transistors),
only diodes which are very reliable too.
Modern design usually dictates using a switching power supply except
in cases where extremely high reliability is required, however recent
advances could be changing this trend.
