12 volt Electrics

House Battery

Following a major melt-down (literally - one cell collapsed, causing gassing, heating and major swelling) of the original Amp-Tech AT121000D deep cycle battery, it was replaced on 28 November 2008 with a Fullriver HGL120-12B AGM (Absorbed Glass Matting) VRLA (Valve Regulated Lead Acid) battery (the only Fullriver model available at the time and place). The battery is claimed to have a 6–10 year life in ideal conditions. Its 120 A-hr rating is specified for a 20 hr drain (i.e., 6 Amp). The size is 331 mm L x 175 mm W x 218 mm TH (the same size as the previous 100 Ahr battery).

The battery is housed in a plastic battery box next to the stove under the bed and is permanently vented to the (driver's) outside by a 50 mm flexible plastic pipe.

An AGM does not normally require an 'equalisation' charge. AGMs are bulk charged at constant current (or whatever the solar panels can supply through the Solar Power Management Unit if it is cloudy) until the battery voltage rises to around 14.4V, after which the voltage is held at that value during the absorption cycle. After a certain time the charger switches to the float mode which drops the voltage to around 13.8V.

Every discharge/charge cycle reduces the life of the battery. The Fullriver HGL series of batteries have a cycle life as shown here for ideal conditions. It seems a good idea to maintain a ~70% state of charge when the battery is in use (~30% depth of discharge), however reaching the occasional 50% state of charge should be no problem so long as the battery is recharged without delay by an adequate independent battery charger or solar cell arrangement.

The state of charge of the battery can be estimated by measuring the resting voltage, i.e. after 6–12 hours of no or very small load. The following Table is taken from www.phrannie.org/battery.html :

Collyn Rivers recommends the upper end of the range of voltages given in this Table (see his Table 1 at www.caravanandmotorhomebooks.com/articles/lead_ acid_batteries.htm.

A better way to monitor the state of charge of the battery is to integrate the (signed) current input to the battery over time. Some expensive solar monitors have this facility. A project to do that for the Applause motorhome is described on another page.

Over time, I have found that the most reliable way to estimate the state of charge of the battery is to observe the charging current from mains hookup or the solar panels. Only when the charging current falls to a low value (say 0.3 A or lower) for about an hour can we regard the battery to be fully charged. A charging current of over 10 A indicates a depleated battery, and over 2 A indicates a battery that will take a couple of hours more to charge.

Elektroblock EBL 269-2

The Schaudt EBL 269-2 Elektroblock charges the battery and supplies 12 V appliances with power. Its functions include:

• The 18 A LAS 1218 charger module
• The 12 V distribution
• Fuses for the 12 V circuits
• Other control and monitoring functions.

The front panel of the Schaudt EBL 269-2 from the documentation:

Battery Charger LAS 1218

The LAS 1218 is a IUoU charger. The capital letters indicate a charge phase during which that electrical property (I for current, U for voltage, W for power) is constant. An IUoU charger has three phases: constant current, constant voltage, constant voltage. The second (trickle charge) phase typically has a lower voltage than phase 2. The following diagram shows this.

Control Panel

The control and switch panel is a Schaudt LT400.

Some comments:

• Eight-step voltage indication of house and starter batteries. These are not very accurate, and seem sensitive to temperature.
• Four-step indication of water tank fill levels for fresh and grey water tanks but these are VERY unreliable; the grey water indicator rarely works at all.
• 12 V Main switch with indicator, Accessories, Lighting and Water switches.
• The PCB includes provision for monitoring the current shunt in the Elektroblock. This is implemented as described later.

Elektroblock Circuit Diagram

A full circuit diagram is included in Schaudt's description of the EBL 269 and is repeated here (click it for a larger version):

Two heavy cable pairs run from a battery/alternator connection in the engine bay directly to the Elektroblock. A single (yellow) cable runs from a D+ alternator connection in the engine bay to the Elektroblock (block 2, pin 3). One of the pairs powers the fridge (through block 2, pin 1) when the D+ line is at 12 V. The other pair provides alternator charge to the house battery (through connector E20-3F on the back of the Elektroblock) when the D+ line is at 12 V and also provides charge current from the Elektroblock to the starter battery when the van is on 230 V mains hookup.

As received, A'van had wired the side step into the water supply circuit, controlled from the Switch Panel. This has been corrected as part of a redesign of the side step control setup (see the changes here) by wiring it to the designated pins of Block 6, which otherwise was not being used at all.

The Schaudt description notes that all consumers of 12 V are switched except:

• Heater
• Step
• AES/compressor refrigerator
• Circuit 1/4 and Circuit 5.

The Schaudt description also notes that:

• A relay in the Elektroblock supplies the AES/compressor refrigerator with power from the starter battery when the vehicle engine is running and the D+ line from the alternator is high (12 V).
• The refrigerator is powered by the house battery when the vehicle engine is switched off.
• An automatic float charge for the starter battery at up to 2 A occurs when the 240 V mains supply is connected to the Elektroblock.

A Note on the D+ Line

The vehicle alternator includes B+ and D+ terminals. The D+ terminal is connected to one side of the ignition warning lamp in the vehicle; the other side of the warning lamp is connected to the starter battery positive terminal via the ignition key switch. When the key switch is initially turned ON before starting the engine some small amps will flow through the key switch, through the bulb and via the D+ terminal of the alternator through the slip rings and rotor winding so that the alternator can initially excite. At this time the voltage on the D+ terminal is close to zero. As soon as the engine starts and the alternator starts to charge the starter battery from the B+ terminal, the voltage at the D+ terminal goes to 12 V or more. This voltage activates a relay in the Elektroblock to connect the output voltage of the alternator at B+ to the leisure battery positive terminal. The Elektroblock also uses this D+ signal to energise another relay to connect the compressor fridge to the starter battery/alternator.

Block 6 on the Elektroblock

Initially not used at all, Block 6 is now very busy. The Eberspächer diesel blown-air heater is connected to Pins 4 and 2; the Omni-Step is connected to Pins 7 and 1; the rear door light (activated by opening the back door) is connected to Pins 9 and 3; and Circuit 1/4 (used at present only to supply the cabinet light under the cooktop) is connected to Pins 8 and 5.

The Block 6 9-pin receptacle on the Elektroblock is labelled as an "MNL socket cap 9x" and is polarised in a particular way, as shown here. A matching plug is TE CONNECTIVITY/AMP 35072-1, a nine-contact housing. Suitable pins are TE CONNECTIVITY/AMP 926900-1, crimp brass pins for 16–13 AWG wire.

The pins and contact housing are available from element14 (formerly Farnell).

Monitoring house battery Current

Monitoring the house battery current consumption gives a check on operation of the motorhome electrics. The Elektroblock EBL 269 has a built-in 1 mV/A shunt accessible from the LT400 Control and Switch Panel. A monitor using that shunt will also show the charging current when the van is plugged in to 240 V power. I have built four versions of the current meter ( ). Versions 1–3 use the Elektroblock shunt, and Version 4 adds a current shunt at the battery so that the total current input to the battery can be monitored.

Current Meter v1

Dick Smith Electronics DSE Q2220 3½ Digit LCD Voltmeter Module is a 200 mV fsd voltmeter. So it will give a direct reading of Amps when connected across the EBL 269 shunt. The meter only draws 1 mA, so the simplest way to power the meter is to use a 9 V battery as follows:

Four-colour ribbon cable to the LT400 Control and Switch Panel is soldered there to points near the main plug connector. There are pads for the current shunt on the circuit board (Pin 1 (yellow) and Pin 4 (orange) near the connector). Since analog voltages for the House Battery (Pin 4) (orange) and Starter Battery (Pin 8) (green) with Common negative at Pin 2 )(blue) are available there too (see the EBL269 circuit diagram), these are made accessible as touch points on the meter box front for reading with a multimeter.

Installed in a wooden box, a photo of the meter is shown with it reading 1.8A consumption (negative current) due to two 10W halogen lights (1.7A) and the LT400 itself (~0.1A). The battery voltage touch points and ammeter power switch are on the left of the meter module. The meter box is attached to the wall by two keyholes in the back, and sliding to the left over countersink-head wood screws.

Current Meter v2

Alternatively, when it is powered from the same battery as it monitors for current, this kind of meter requires a dual power supply with common-mode input voltage well between the supply voltages. An attempt to implement this was made with the general idea as follows:

The negative supply is easily provided, using a 7905 to provide -5V relative to voltage (1), the Load. A positive supply relative to voltage (1), the Load, requires addition of a voltage pump. One was made based on an NE555 IC running as an astable, the output of which was rectified to pump up a capacitor to a positive voltage. While this worked, there was a non-zero reading when the inputs were shorted: this could not be resolved for quite a while. It turns out that I had made a fundamental error of precision metering, namely the meter was drawing current from one of the sensor wires and the impedance of that wire is sufficient to cause a voltage drop of a couple of millivolts - the observed offset.

Final Current Meter

While puzzling over why v2 did not work, I came across kit K212 from Oatley Electronics, a $9.00 panel meter interface kit that is designed to allow the kind of digital panel meter I am using to measure its own supply voltage.

The kit bolts onto the back of their DPM1 panel meter (cheaper than DSE's) so I bought one of these too. The new circuit uses the kit's DC to DC power supply, the on-board variable resistor set for battery voltage measurement, and a 4-pole 3-position break-before-make rotary switch (DSE P7520) to give readings of consumer current (from the LT400 current shunt pads), using the current shunt added during the rewiring of the house battery for the State of Charge monitor gives total house battery current, and house battery voltage. A 500mA fuse and small slider switch are added. Five-strand ribbon cable is used to connect the circuit to the LT400, and a separate cable connects to the battery shunt.

The DC to DC power supply circuit is:

and the selector switch wiring is:

The selector switch gives:

1. Current consumption via Elektroblock (-ve)
2. Total current input to house battery (+ve)
3. Voltage of house battery.

Notes:

• Since realising that the power to supply the meter should not be obtained from a shunt lead (because any voltage drop is seen as an offset on the meter), I use Pin 11 on the LT400 connector, the Battery Sensor (red ribbon), as the 12 volt input to the DC to DC supply.
• The floating DC output from the DC to DC supply had a lot of common mode noise, including 455 kHz stuff from the IF transformers on the board. This is largely removed by adding a 0.1 µF capacitor to ground the output with respect to AC.
• Using an oscilloscope I also found a lot of noise on the wiring from the Elektroblock, especially on the shunt leads. So I have added an inline filter to the inputs to the panel meter from the rotary switch (wipers A and B).
• The third set of contacts on the rotary switch (C and 7, 8, 9) switch an adjustable voltage divider across the terminals of the batteries to bring the voltage into the range of the panel meter (0-199.9 mV)
• The fourth set of contacts on the rotary switch (D and 10, 11, 12) is used to switch the decimal point on the display for battery current (0-199.9 A) and battery voltage (0-19.99 V)
• The inline 500 mA fuse proved essential: I blew it three times during testing when I slipped with test probes.

Monitoring Status of Roof Equipment

I have added a panel below the current meter with a set of LED lights and switch to give the status of the TV antenna (whether up or down), of the deployable solar panel (whether out or packed), and whether the shower room hatch and the main skylight are closed. Half the panel is blank, awaiting new ideas.

The TV antenna has a new tilt switch ( Jaycar #SM1035) added and the cable for this is fed down the kitchen rangehood vent pipe to the monitoring panel. The deployable solar panel has a pin switch ( Jaycar #LE8777) located on one side that opens when the panel is latched down for travel. Its cable also feeds down the rangehood vent pipe to the monitoring panel. And the two roof vents (hatch and skylight) each have a magnet attached that closes a reed switch (Altronics #S5154B) when the vent is closed. These two switches are in series, so both vents have to be closed for the indicator on the monitoring panel to show ready for travel (green).

A bipolar LED ( Jaycar #ZD0248) is used to display green or red. Each LED is driven by two of the four Op Amps in each of two LM324 packages ( Jaycar #ZL3324). The LM324's differential input voltage range can be the full power supply voltage, so there is no need to include resistors on the inputs. There is also no need for controlled hysterisis on the positive feedback from one Op Amp to the other, since the control signal is a simple switch.

The circuit works as follows: with the switch open (e.g., TV antenna parked) input pin 2 is high so output pin 1 is low compared to the mid voltage at input pin 3. So input pin 6 is low and thus output pin 7 is high and the green LED lights. When the switch is closed (the antenna is up) input pin 2 is low so output pin 1 is high, input pin 6 is high and output pin 7 is low and the red LED lights. Power consumption is ~18.3 mA green, 19.0 mA red. Only one circuit includes the divider string of resistors. All others use that mid voltage reference. And the circuit for the roof vents has the LED reversed since the switch is closed when the vents are closed. The fourth circuit and LED are unused so far.

The panel switch is very similar to those on the Schaudt LT400 control panel, and is a modified mini-SPDT centre-off spring return both sides ( Jaycar #SK0987). The rocker markings have been removed using Brasso, and the spring and bridge have been removed from one side of the mechanism to make the switch a spring return one side, latching action the other side.

LINKS

• A'van http://www.avan.com.au
• Schaudt Systems http://www.schaudt-gmbh.de
• Advice on Batteries etc.http://www.phrannie.org/battery.html
• element14 http://au.element14.com
• Dick Smith Electronics http://www.dse.com.au
• Oatley Electronics http://www.oatleyelectronics.com.au
• Jaycar Electronics http://www.jaycar.com.au
• Altronics http://www.altronics.com.au

Electrics

The EBL 269 elektroblock current shunt.

Version 1 wiring of Control Panel to access current shunt and battery voltages information for Applause

Version 1 Current Meter mounted below Control Panel for Applause electrics

Version 3 wiring of Control Panel to access current shunt and battery voltages information for Applause

Back of Version 3 Current Meter: DC-DC isolator, meter input filter, voltage divider, and 4 pole 3 position rotary switch.

Version 3, 4 Current Meter below LT400 panel.

Circuit board for TV antenna and solar panel monitoring. The two bipolar LEDs on the right are not yet used.

The partly-populated lowest panel indicates the travel status of the TV antenna, solar panel and the two skylights on the roof.