An Addition to the Trickle Charger

Radio Record, Volume II, Issue 24, 28 December 1928, Page 27

An Addition to the Trickle Charger

Contributed by

W.

Winten

Ty the issue of the "Radio Record" for November 28, a trickle-charger foy both A and B batteries was deribed. It is quite an efficient device. I€ saffers only from one.disadvantage, namely, that to put batteries in charge requires their removal from the set, which is earthed, and this is a messy business-and one slip with the B battery wires may cost the radio fan a new set of valves, and anyone who has had the misfortune to burn out a set of ‘six or eight knows that this is a costly business. This addition is in the form of a switch which has three positions, viz., batteries disconnected, batteries to set, and batteries to -charger-no wires to remove, or connections to change. The "off" position is an advantage, especially where 135 volts or upwards is used, for when only the filament switch is turned off, and the B’s left connected, there is a strain on the insulation of the set; and, also, this practice leads to electrolysis, at joints especially. To make this switch, little skill is required, and few tools; in fact, any constructor who has made the charger can build it in a couple of hours. Of course, it can be applied to charging devices other than the one mentioned in the article. The list of material is as follows :- 1 piece of insulating panel 3-16in. thick or over, 4in. x #in. . 1. piece of insulating panel, ‘ebonite, ete, 4in. v. 4in. 1 piece "hard .brass, #in. x 12in. x 3-64in. 1 piece hard brass, 3}in.-v. 33 in, x 8-64in. 19 5-32in. bolts.and nuts lin. long. ) 1-8in. bolts and nuts jin. long. 14 §-32in. nuts. . Square up the 4 x 4 panel, file the opps up true and slightly level that "ae which is to be the face, all round. Now on the back of the panel draw two centre lines at right angles, and on the horizontal one mark two points each side of the vertical line fin. apart. Parallel to the horizontal line, draw two more lines 1 1-8in. either side of it. Mark these the same as the centre horizontal with two marks each side #

of an inch. Each of these marks may be drilled 5-32, excepting that one blank is left on the top line, the second from the right, looking at the back. Four small holes may be drilled to hold the switch and the charger, or wherever it is mounted. From the larger piece of hard brass the switch contacts are made. This piece is cut into strips 14 inches long by + inch wide, a 5-82 hole is drilled through the centre, a bolt.inserted, and then the piece is bent into a U-shape with the tips close together. Fourteen pieces thus are required, but five of them require a little further treatment. These five are for the centre

row and are the contacts that the switch blades pivot on. They have an 1-8 inch hole drilled through the contact faces to take the blades. The blades are made from the second piece of brass and are 7 inch wide by 2 inches long. Five are required. Through one end an 1-8 inch hole is drilled, just slightly back, and the corners this end are rounded off. Now from five of the 5-82 bolts cut pieces 4+ inch long and slit them with the hacksaw for 8-16 of their length. Solder the switch blades in this slot, the end with the hole in, of course, not being soldered. ; Insert one blade in each centre con tact and bolt up stiffly with the 1-8 inch bolts, filing any projecting length away. Now mount this much on the panel ‘together with all. the other contacts. The piece of 4 inch panel is to form the link bar of the switch, and is drilled to take the short pieces of screws on the switch blades. A nut on each projecting thread holds it on. A small handle may be mounted on the centre blade if desired. The extra nuts are to make the con-: nections with the leads: to the batteries at the back. If your B bat-

tery has more than three leads, an extra blade will be required on the switch, but the method of connecting it will be obvious as the only two contacts required for the B battery on the charge side are B+ and B-. The diagram will give the constructor an idea of the finished switch. If a © battery is used it must be connected with the C+ terminal joined to the A- contact on the "to set" side of the switch, and not to the A--~ terminal on the battery. © To charge the batteries is now quite a simple matter. The switch shown in circuit with the primary of the transformer in the original article may be transferred to the A- side of the

charger terminals, and the charger controlled by the plug switch on the outlet to which it is attached. This will allow the B to be boosted on its own. To charge the A battery only, remove the resistance lamp from its holder,