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A 2kW 24V/240VAC sinewave inverter; Pt.5 In this fifth & final instalment on the sinewave inverter, we present the assembly details of the chassis and the setting up procedure. Quite a lot of wiring is involved, especially that associated with the DC-DC inverter & H-pack boards. By JOHN CLARKE · The complete kit for the ZkW Sinewave Inverter (from Rod Irving Electronics) will include the assembled DC-DC inverter transformer, Tl. This transformer requires careful construction techniques. The 1-turn copper sheet primary windings must be carefully terminated in order to obtain an 80 SILICON CHIP exact balance between them, while the secondary is quadrifilar wound with 2mm enamelled copper wire. The chassis for the inverter has removable side panels and lid. The DCDC inverter and H-pack PC boards, together with the associated Mosfets, IGBTs and diodes, mount onto the side panels which each have two vertical heatsinks. Rectifier diodes D3D6 are mounted on the rear panel. The assembly procedure given in this article assumes that all metalwork has been drilled. Ifnot, you will naturally have to drill all holes before assembly begins. The wiring involves heavy duty cables capable of carrying 130 amps, plus mains-rated cable and light duty wiring between the PC boards. Because there is such a large variation in the wiring, we recommend that you follow this article and the wiring diagram very carefully. Transformer board We will begin with the transformer board, since this requires a considerable amount of mechanical assembly and wiring. This is a bare fibreglass board measuring 175 x 370mII_l and it accommodates the DC-DC inverter transformer (Tl) and associated components. As supplied, the two Clipsal BP165C12 brass link bars have 12 pairs of screw terminals plus a 5/16-inch bolt at one end. Both these bars are cut to give one block with a bolt and two pairs of terminals and one block with nine pairs of terminals. To do this, remove the two screws at the third pair of terminals (near the bolt) and cut the bar across the centre of these screw holes. Clean up each end with a file. One of the short ends with the bolt, designated LB3, is used to mount fuse Fl. The two 9-pair terminal blocks are designated LB4 and LB5. You will need to drill a mounting hole at the cut end for each of the LB3, LB4 and LB5 terminal blocks. Termina~ strips Three 4-way 30A insulating terminal strips are required for the inverter and these are cut from the 12-way 30A terminal strip (Clipsal BP535 or 593/30) using a sharp knife. If the transformer board has been supplied undrilled, you will need to mark it out and drill it before assembly can begin. To do this, arrange the components as shown on the wiring diagram. The LB1, LB4, LB5 and LB6 terminal blocks are placed with their outside edges about 5mm away from the edge of the board. Note that the LB1 block bar must have its top edge about 40mm from the top edge of the board to allow space for the bank of five l0µF capacitors. LB2 is located 28mm away from LB1. Similarly, the bottom edge of LB6 should be spaced 30mm back from the adjacent edge of the board to provide room for the three lOµF capacitors. A gap of 10mm separates LB7 from LB6. LB2 and LB3 must be correctly spaced to allow fuse Fl to be bolted between them. Transformer Tl is mounted with its righthand bobbin in line with the righthand edge of the board and is secured with two bolts. These bolts pass through a sheet metal retaining clamp which sits on top of the transformer. This retaining clamp also sup- This close-up view shows how inductors L3 & L4 are secured to a fibreglass board using an 8 x 80mm bolt & nut. This board is then mounted vertically on the rectifier board using two right-angle brackets. ports a 4-way 30A insulating connector strip. When you have positioned all the hardware on the board, mark out all the holes and drill them. That done, you can mount the transformer and the associated hardware. The transformer should be mounted with the primary wires close to the board and the red secondary wires directed towards fuse Fl. Four pieces of copper sheet measuring 28 x 60 x 0.6mm will be needed for mounting the 10µF supply bypass capacitors - see Fig.20. These will have to be drilled or punched so that they can be retained by the 5/16-inch bolts on blocks LB1, LB2, LB6 and LB7. They will also need to be drilled to accept the leads of the lOµF capacitors. Five lOµF capacitors mount be- tween LB1 and LB2, while three lOµF capacitors mount between LB6 and LB7. The capacitors are soldered to the copper plates before they are mounted onto the brass terminal blocks. Note that the copper sheet mounted on LB2 is located beneath the lug of fuse Fl. The two copper sheets which mount onto blocks LB6 and LB 7 are each secured with a 5/16-inch bolt and two screws, as shown on the diagram of Fig.20. 130-amp cables Short black and red 130A cables are used to connect LB1 to LB6 and LB2 to LB7. These should be kept as short as possible to minimise any internal voltage drop due to resistance and inductance. If necessary, you will need to strip each end and fit suitable FEBRUARY 1993 81 130A CABLE (BLACK) - X' THERIIAL CUTOUT TH1 TO THERIIAL CUTOUT TH2 y• J SOLDER LUG BOLT TO REAR f'ANEL ........- - - . . - 10uF ,-- COPPER SHEET 10uF TO RECT. PCB 130A CABLE (RED) I 1 Q' FUSE2 FRONT PANEL LB1 ~ ©©© © © E' © <at>F' © <at>G' © <at>H' © <at>I' © DC·DC INVERTER PCB SC11309921 7 TO SINE PCB <at> R<at> TRANSFORMER T1 21r 30A CONNECTOR STRIP CS2 o© TO FRONT PANEL p<at> © © © © © © --~-~-. . . Q8 Q7 Q8 Q9 0 0 0 0 v •s ~T •z *A· ~u ~v *B· \..:..:,w Q1 © B' © A' ©z ©v 0 LBS •c· '-:..::x V • 30A 240VAC INSULATED WIRE 0 0 LB8 0 0 s T w 0 0 FIBREGLASS SHEET 10uF COPPER SHEET 10uF 0 COPPER SHEET 10uF terminal lugs to them using an p.ydraulic crimping press or by soldering them with a blowtorch. If you don't have these facilities, an 82 SILICON CHIP auto electrician will be able to do the job. The main 130A supply leads will also need to be fitted with suitable lugs and battery terminals. These are terminated in a similar manner to the cables described above. Do not connect the battery leads at this stage, since the transformer board MOUNTED ON BACK PANEL - - ....... , 05 06 03 04 T O D C - D C X ' ~ THERMAL INVERTER PCB AND CUTOUT TH1 Y' TH2 Q19 ~ ~ 012 RECTIFIER PCB SC11309924 L4 8x80mm BOLT AND NUT L3 •A •F •C m•B ~•E w•D ~•G ~•H z 1uF 500VAC +365V Cl) o•J 1-.K •L •M •N A• F• H-DRIVE PCB SC11309922 c• B• E• O•~ G• w H•~ I•~ J • =i: K•O IL• M• N• t15A MAINS WIRE DELTA 10DRCG5 EMI FILTER SINEWAVE PCB SC11309923 TO FUSE 5 t15A INSULATED MAINS WIRE has yet to be mounted inside the case. However, you can secure the cables in position between LB1 and LB6 and between LB2 and LB7. Note that the TO EARTH OF GPO TO N OF GPO Fig.20: follow this chassis wiring diagram carefully when wiring up the inverter be sure to use the specified grade of wire for each connection. In particular, note the two 130A cables linking LB1 to LB6 & LB2 to LB7. The two thermal cutouts (TH1 & TH2) are mounted on the side panels immediately adjacent to the heatsinks at the back of the chassis. & FEBRUARY 1993 83 using three short lengths of 15A mains cable. When wiring the CS1 terminal strip, make sure that the secondary wires from bobbin 1 connect to the two lefthand terminals and that the secondary wires from bobbin 2 connect to the two righthand terminals. The blue and brown output wires which connect to the opposite side of CS1 should not be connected until the transformer and rectifier boards have been installed in the case. Chassis side panels The two thermal cutouts are secured to the side panels using machine screws & nuts. If the heatsink temperature rises above 80°C, these cutouts open & switch off the power to the DC-DC inverter circuitry. As mentioned previously, the two side panels of the chassis are used to support the DC-DC inverter PC board and the H-pack PC board. Each board is mounted centrally on its respective side panel on four 6mm metal standoffs. Before going further though, it's a good idea to check that all the mounting holes have been deburred. This will prevent damage to the mica insulating washers that are used to isolate the power semiconductor devices from the chassis. The first step in assembling the side panels is to fit the four heatsinks. To ensure good thermal transfer, apply heatsink compound to the back of each heatsink before attaching it to its respective panel using two screws (one at the top and one at the bottom). The PC boards can now be mounted on the 6mm standoffs. The power semiconductors for the H-pack PC board - IGBTs Q17-QZ0 and diodes D10-D13 - are mounted as shown in Fig.23. Note that two mica washers are used between the tab of each of these devices (Q17-Q20 & D10-D13) and the side panel. This is to prevent Diodes D3-D6 are bolted to the rear panel for heatsinking. Note that they must be insulated from the panel using mica washers & mounting bushes. copper sheets that carry the 10µF capacitors go underneath the cable lugs. Wiring the transformer board The primary wires from the transformer are connected to brass link bars 1B2, 1B4, 1B5 and 1B7 as shown in Fig.20. The four blue primaries connect to 1B4, the four black primaries to 1B5, the four yellow primaries to 1B2 and the four red primaries to 1B7. Cut these leads as short as possible while still allowing a small amount 84 SILICON CHIP of slack when they are connected. They can then be laced together neatly with cable ties. The secondary leads terminate at insulated connector strips CS1 and CS2 (two leads in each terminal). Cut the leads so that a small loop is formed between the transformer and terminal and strip back the plastic sleeving and enamel coating before securing the wires into the terminals. The terminals on the opposite side of connector strip CS2 are interconnected high voltage punch-through of the mica washers. Apply a smear of heatsink compound to all mating surfaces before securing each device with a screw and nut. This done, use your multimeter to check that the metal tab of each device has been correctly isolated from the chassis. The power MOSFETs on the DC-DC inverter board should not be secured to the side panels at this stage. This is because the tabs of these devices are wired to the link bars on the transformer PC board and we're not up to that stage yet. Rectifier board assembly This partly assembled board can w u, ir 31:: <at> ~ ..-z ~~nz ~1~ :c 0 "' - I < w z ~al 0 <at> ~i ~ tw <C ~e -' w z a. 0 ,- :: 0 "' < al iO -' w z a. < a. 0 ,- ,z 0 ff: 0 ,- Fig.21: this diagram shows how the parts are arranged on the rear panel, as viewed from inside the chassis. now be completed. The 4-way 30A terminal strip is mounted on the board with screws and nuts, while the 680µF 400VW filter capacitor is mounted using its integral stud, star washer and nut. The 25µF 370VAC capacitor is mounted with a 45mm-dia. collar bracket. Fig.22: the inside front panel layout. Sleeve the fuse terminals with heatshrink tubing to prevent shock. The toroidal sinewave filter inductors, L3 and L4, mount side-by-side on a vertical piece of bare fibreglass board (100 x 55mm). This board is secured to the rectifier board using two L-shaped brackets. Note that the vertical board has a rubber grommet to allow the wires from L4 to pass through it and thence to the 30A terminal strip. • L3 and L4 are secured to the vertical board with a bolt which passes through their centres. This is fitted with a nut and 45mm washers at each end. The L-shaped brackets are secured to the rectifier board using two FEBRUARY 1993 85 NUT CI:J:l WASHER= - -- - - INSULATING WASHER c:::=========::l CHASSIS HEA TSINK FOR ...__ _ _ _ _ _ __. Q5-Q20, D10-D13 screws which do double duty in retaining two board standoffs). Chassis work Now is the time to assemble the components inside the chassis. As shown in Fig.21 (back panel), the two cable glands are each mounted with the securing nut inside the case. With those fitted, the transformer board, sinewave board and rectifier PC board can all be mounted on standoffs inside the case. The 15A EMI filter can also be mounted at this stage. The front panel hardware can be mounted next. This hardware comprises the front panel label, the two fuseholders, power switch S1, LED1 Fig.23: this diagram shows the general mounting details for the TO-220 devices. Smear all mating surfaces with heatsink compound before bolting the various assemblies together & note that two insulating washers must be used with Q17-Q20 & D10D13 to prevent voltage punchthrough to chassis. and the mains GPO (double power point) - see Fig.22. The positive and negative battery leads are passed through the glands and bolted to the LB3 and LBl terminals on the transformer board. This done, tighten the gland nuts (from outside the chassis) to anchor the leads and prevent any stressing of the transformer board. The O. lµF capacitor associated with LB 1 can now be mounted. One lead is soldered to the copper sheet while the other lead is connected to a solder lug which is fixed to the rear panel of the chassis. Diodes D3-D6 are mounted on the rear panel using insulating bushes and WARNING! The internal wiring of the 2kW inverter is highly dangerous. There are lethal voltages present while the inverter is running and these can remain even after the inverter has been switched off. Before touching any part of the inverter circuitry, always check the DC voltage across the 680µF 400VW capacitor terminals. This capacitor is extremely dangerous when fully charged and can only be regarded as "safe" when the voltage across it is below 20V. This voltage is reached a couple of minutes after the inverter is switched off. As an extra safety precaution, always place the lid on the inverter before powering up. The lid will protect you from flying debris if there are any catastrophic component failures. Don't be rash-this can happen. At the very least, wear eye protection. You should also take considerable care with the battery bank. Ideally, batteries used indoors with inverters or uninterruptible power supplies should have explosion proof vents and should be housed in a separate cabinet. Even so, there is still a risk of explosion since there is a risk of hydrogen being present after charging. Always switch the inverter off before connecting or disconnecting the battery leads to avoid sparks occurring at the battery terminals. Note that a small spark may occur when first connecting the battery leads, even with the inverter switched off. This is due to the charging current into the eight 10µF capacitors connected across the supply leads. 86 SILICON CHIP mica washers. Use heatsink compound on the metal tabs and the mating surface of the rear panel to ensure good heat transfer. Check that the metal tab of each device is isolated from the rear panel by measuring the resistance with a multimeter. Chassis wiring Start by wiring between the DC-DC inverter board and the transformer board. The blue and brown output wires (15A cable) from the DC-DC inverter board to the rectifier PC board are connected using 6mm crimp eyelet lugs. These lugs are secured using screws which thread into nuts that were previously soldered underneath the board. The sources of MOSFETs Q5-Q10 are connected to LB6 on the transformer board, while the source wires from Q11-Q16 are connected to LB1. The source wire connections are made via crimped eyelet lugs which are retained by 4mm screws to the PC board. The connections to the drains of Q5-Q16 are made (using 15A cable) in a similar manner, with the eyelet lugs being placed directly against the metal tab and under the insulating bush of each MOSFET (see Fig.23) . The drain leads from Q5-Q10 go to LBS, while the drain leads from Q11-Q16 go to LB4. Tie the wires into neat bundles with cable ties and then secure the side panel to the chassis. The low current wiring is run mainly using heavy duty (10A) hook-up wire. The exception is the shielded cable that's run between the rectifier PC board and the DC-DC inverter board. Three supply leads run from the DC-DC inverter board to the sinewave generator board, while 14 leads run from the sinewave board to the Hpack drive PC board (refer to the board testing procedure described last month). Finally, there are the leads from LB1 (positive side of fuse Fl) to the front panel switch S1, from LB6 to the DC-DC inverter board, and from the DC-DC inverter board to the thermal cutouts. The thermal cutouts (TH1 and THZ) should be wired before they are secured to the chassis. When running the shielded cable from the DC-DC inverter board to the rectifier board, use heatshrink sleeving • . . ... FLUKE AND PHILIPS - THE GLOBAL ALLIANCE IN TE ST & MEASUREMENT • FLUKE®• • • • J ♦ ♦ • 7 0 • • ♦ ♦ • S E R I E S e PHILIPS ♦ I I We've improved on a winner If you've waited for the next generation · digital multimeter technology, you've made the right choice. Now there is the new Fluke 70 Series II. We've made the world's most popular DMM's even beaer. 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Instrumentation, J.Blackwoods & Son, Lawrence & Hanson, Macelec, Novocastrian, Obiat, Stott Ind. Suppl., Tech Fast, Tecnico, Vincom. ACT: Advanced Instrument Services, Aeromotive Maintenance, John Pope Electrical. VIC : Auslec, Emcorp, Factory Controls, Consultant Technologies, David Reid Wholesalers, OGE Systems, Ebson, Elect. Smith Projects, J. Blackwoods, Parallel Systems, Radio Parts Group. ALL STATES: BEP, Dick Smith Electronics, GEC, Petro-Ject. Best of a!L every 70 Series II is a Fluke, . backed by a worldwide service network and 3-year warranty. Be N .1 'th Fluke and Philips OLD: Austec, Colourview Electronics, Emcorp, Industrial & Marine Electrics, J .Blackwoods, LE. Boughen, Mass Electronics, Nortek, Solex, St. Lucia Bectronics, Thomson Instruments. S.A: AW.M. TAS: George Harvey. W.A: Atkins & Carlyle, Leda Electronics, R.S. Components. N.T: Industrial Suppliers & Switchgear J.Blackwoods. PHILIPS • This is the view inside the fully completed prototype. Check all wiring carefully when it is completed & be sure to follow the low-voltage test procedure outlined in the text before applying full power to the inverter. over the cable ends to provide stress relief. High voltage wiring The high voltage wiring involves the rectifier and H-pack drive boards, phis the output to the mains filter, GPO and associated fuse. This wiring must be run using 15A mains-rated cable, much of which is terminated 88 SILICON CHIP using crimped lugs. Use star washers under all the screws to ensure good connections to the wiring lugs. The connections to the 25µF 370VAC capacitor and to the mains filter are made using female quickconnect crimp lugs. Make sure that the earth connections from the mains filter to the chassis and from chassis to the earth terminal of the GPO are made with the correct green/yellow striped mains wire . . The high voltage wires to the Hpack drive board are fitted with eyelet crimp lugs secured with a star washer and screw. Don't forget to install the 1µF 500VAC capacitor between the +365VDC terminal and the 0V terminal. Testing The 2kW Sinewave Inverter comprises a large number of expensive The mains filter at the front of the chassis is necessary to reduce high frequency interference to television & radio reception. components which can be damaged with catastrophic results if there is an error in' the construction or wiring. After you have finished your wiring, we recommend that you check each lead against the wiring diagram and then against the relevant circuit diagram just to make sure that all is correct. If you don't, the bill for blown components can be quite high. We recommend that you follow the testing procedure to the letter. Low voltage test Before testing the inverter fully, it is wise to check that the high voltage circuitry will operate at low voltage. To do this, disconnect the low current +24V lead from 1B3 and connect a clip lead between this lead and the +365V terminal on the H-drive PC board. This done, connect a clip lead between the negative terminal of the 680µF capacitor on the rectifier PC board and the negative battery lead. Finally, remove fuse F4 from the rectifier PC board. This allows the entire circuit to operate at 24V, including all the high voltage circuitry. Now connect a 24V power supply between the negative battery lead and the low current +24V lead (do not connect power to the positive battery lead). This will power the inverter drive circuitry but not the MOSFETs (Q5-Q16). Consequently, the DC-toDC inverter section of the circuit will not be running but the 24V applied to the H-drive circuitry will produce a low voltage sinewave at the mains GPO. An oscilloscope can be used to monitor this sinewave at the GPO. If the power supply you are using is fully floating (ie, neither of its outputs is grounded), you can use one probe to earth one of the GPO terminals. If the power supply is grounded, then the oscilloscope must be used in its differential mode to avoid shorting the supply output. Note that there will some distortion in the output sinewave due to the voltage drop across the IGBTs in the H-drive circuitry. In normal operation, this distortion will not be present since the voltage drop across the IGBTs will be negligible in comparison to the 365V supply. When operation at 24V has been confirmed, a full voltage test can be run. You will require a 24 V battery (or two 12V batteries.in series) which is capable of supplying 120A for at least 15 minutes. Restore the wiring inside the ZkW Sinewave Inverter to its normal condition and re-install fuse F4. Rotate trimpot VRl on the DC-DC inverter PC board so that its wiper is pointing directly upwards. This should set the output voltage at just below 240VAC. Before connecting the inverter to the batteries, it is advisable to install a 15A automotive fuse in the positive battery lead in place of fuse Fl. This will blow well before any damage can occur if a fault is present. This fuse can be supported by two stout lengths of tinned copper wire attached to 1B2 and 1B3. Now replace the lid on the inverter. Make sure that the inverter is switched off, then connect the battery leads (with the 15A fuse in circuit). Connect a digital multimeter set to read 240VAC to the GPO socket and switch on the inverter. The AC voltage should quickly rise to over 200VAC (this can be adjusted later with VRl) and the 15A fuse should remain intact. If a DC clamp meter is available, measure the DC current supplied to the inverter. It should be about 3A for no output load. Switch off the inverter immediately if you smell anything burning and correct the problem before switching on again. Be sure to follow the safety precautions outlined in the warning panel when working on the inverter. For further testing, you will need some loads. Several 100W light bulbs connected in parallel using bayonet holders are useful, while a bar radiator can provide a 2kW load. The inverter will drive a 300W load using a 15A fuse in place of Fl. Measure the AC voltage across this 300W load and note the reading. This done, switch off the inverter, disconnect the battery and remove the lid. Now measure the DC voltage across the 680µF capacitor and wait until it drops to less than 20V. When it does, rotate VRl slightly clockwise if the output voltage was less than 245VAC for a 300W load and slightly anticlockwise if the voltage was greater than 245VAC. This done, check the output voltage across a 300W load again and readjust VRl as necessary. Once the inverter is operating correctly at 300W, disconnect the 15A fuse and re-install fuse Fl. The inverter is now ready for testing at loads up to 2kW. To do this , run the inverter at 2kW and check for excessive l;ieat from the heatsinks at the side of the case. The MOSFETs will normally run quite a lot warmer than the IGBTs. The DC current drawn from the inverter will be about 110A. After operating the unit for a few minutes, switch it off and check the internal components for overheating (be sure to observe the safety precautions). Note that 13 and 14 will normally run quite hot at full load. Finally the sine waveform can be checked using an oscilloscope. The waveforms should be similar to those published on page 30 of the November 1992 issue of SILICON CHIP. SC FEBRUARY 1993 89