Electric starter for a car. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electric starter for a car. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Many motorists have a problem with starting the engine in frosty weather. This is due to two main reasons:

1) voltage drop at the terminals of the ignition coil up to 7 - 9 V;
2) a decrease in the capacity of the battery by 30 - 40% due to a decrease in the temperature of the electrolyte.

If there are many ways to solve the first reason (multi-spark electronic ignition), then for the second, the author suggests using an electric starter.

The use of an electric starter will allow motorists who operate a car in winter to start a cold engine even with an incompletely charged battery, and will also help extend the life of the latter.

Calculation. Carrying out an accurate calculation of the magnetic circuit of the transformer is impractical, since it is under load for a short time, especially since neither the brand nor the technology of rolling the electrical steel of the magnetic circuit is known. Therefore, the author proposes an approximate calculation of the electric starter transformer.

We find the required power of the transformer. The main criterion is the operating current of the electric starter Istart, which is in the range of 70 - 100 A. Electric starter power (W)

Rap = 15 Istart.

Determine the cross section of the magnetic circuit (cm2)

S = 0,017 x Rep = 18...25,5 cm2.

The electric starter circuit (Fig. 1) is very simple, you just need to correctly install the transformer windings. To do this, you can use toroidal iron from any LATRA or from an electric motor.

Electric starter for car
Ris.1

For the electric starter, I used the transformer iron of an asynchronous electric motor, which I chose taking into account the cross section. The parameters S = av (Fig. 2) should not be less than the calculated ones.

Electric starter for car
Ris.2

The stator of the electric motor has protruding grooves that were used to lay the windings. When calculating the cross section, they are not taken into account. You need to remove them with a simple or special chisel, but you can not remove them (I did not delete them). This only affects the flow rate of the primary and secondary windings and the mass of the electric starter. The outer diameter of the magnetic circuit is within 18 - 28 cm. If the cross section of the stator of the electric motor is larger than the calculated one, it will have to be divided into several parts. With a hacksaw for metal, we cut the outer ties in the grooves and separate the torus of the required cross section. With a file, we remove sharp corners and protrusions. On the finished magnetic core, we carry out insulating work with varnished cloth or fabric-based insulating tape.

Now we proceed to the primary winding, the number of turns of which is determined by the formula:

n1 = 45 U1/S,

where U1 is the voltage of the primary winding, usually U1 = 220 V; S is the cross-sectional area of the magnetic circuit.

For it, we take a copper wire PEV-2 with a diameter of 1,2 mm. Pre-calculate the total length of the primary winding L1.

L1 \u2d (2a + XNUMXc) Ku,

where Ku - stacking factor, which is equal to 1,15 1,25; a and b - the geometric dimensions of the magnetic circuit (Fig. 2).

Then we wind the wire on the shuttle and install the winding in bulk. Having connected the leads to the primary winding, we process it with electrical varnish, dry it and carry out insulation work.

Number of turns of the secondary winding

n2 = n1U2/U1,

where n2 and n1 are the number of turns, respectively, of the primary and secondary windings; U1 and U2 - voltage of the primary and secondary windings (U2 = 15 V).

The winding is carried out with an insulated stranded wire with a cross section of at least 5,5 mm2. The use of a busbar is preferable. Inside the wire we place a turn to turn, and on the outside with a small gap - for uniform arrangement. Its length is determined taking into account the dimensions of the primary winding.

We place the finished transformer between two square getinax plates 1 cm thick and 2 cm wide more than the diameter of the wound transformer, having previously drilled holes in the corners for fastening with tie bolts. On the top plate we place the conclusions of the primary (isolate) and secondary windings, a diode bridge and a handle for transportation.

We connect the outputs of the secondary winding to the diode bridge, and equip the outputs of the latter with M8 wing nuts and mark "+", "-".

The starting current of a car is 120 - 140 A. But since the battery and the electric starter operate in parallel, we take into account the maximum current of the electric starter 100 A. Diodes VD1 - VD4 type B50 for an allowable current of 50 A. Although the engine start time is short, it is advisable to place the diodes on radiators.

We install any switch S1 for a permissible current of 10 A. The connecting wires between the electric starter and the motor are stranded, with a diameter of at least 5,5 mm in different colors, and we equip the ends of the terminal lugs with crocodile clips.

Author: V.M.Bosenko

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