E-News Issue #35
One of our staff purchased a Tiffany bread maker for $80. It works OK on a Silver Series Selectronic inverter (modified square wave).
After waiting months to find a supplier, we are sorry to report that the brand we found are rather 'dim and yellow'. They need a rather high voltage before they draw their rated power (26.4V for the 20W and 25.3V for the 35W). We think we've located another brand which we should get in a few days. We'll keep you posted. Let me know if you want to return any for credit.
Plasmatronic Temperature Sensor
A software bug has been discovered in the PL40 so that it will not pass more than 14.4A if the temperature is below 20 degrees C and only if a temperature sensor is connected. If you have such a set up (PL40 + temp sensor + a current of 14+Amps) please contact our office.
Solar Power for Motorhomes & Caravans
This month's longer article is by David Benton of Self Power in New Zealand.
A growing number of people have some sort of mobile home. They range from little pop-top caravans, to full size coaches, and use varies from the occasional weekend away in summer, to the year-round full-time home. Virtually all of them have battery powered lighting of some kind, and they could all benefit from having solar charging their batteries.
The most obvious benefit would be that they could park in one spot for longer without having to start their motor to charge the battery. The battery should also last longer because it has not been discharged for 3 - 4 days then recharged; but been recharged daily by the solar panel.
As with a house solar system we first look at what power requirements there are (and future ones) before designing a solar system to suit. Most mobile homes come with both a 12 volt DC (battery) and a 230 volt AC power system installed. The battery system is usually charged from the engine alternator, and the 230 volt power is supplied through a cable with a caravan plug that is plugged into power outlets at campgrounds etc.
There is no doubt in my mind that electric lights are the best. Candles are dangerous, gaslights fiddly - you can't beat the convenience of flicking on an electric light. Even the smallest caravan will have a couple of 12 volt lights, often car tail light bulbs (20 watts) in a round light fitting. These are OK, and can be modified cheaply to take halogen bulbs, which will give twice as much light for the same power consumed.
A fluorescent light would be even more efficient, giving around 4 times the light of an ordinary bulb for the same power consumed. These are available in compact strip lights, which suit RVs.
Because space is relatively restricted, placing of lights is very important and it is probably better to have more small lights, rather than a couple of big ones in the middle of the van.
Larger vans will also have separate 230 volt lights, that can only be used when the main cable plugged into a mains power outlet. Compact fluoro lights could be used in these, and a inverter used to power these from the battery. (A two way switch is necessary, consult a electrician).
I think it is best to convert these lights to 12 volt operation, and then run them from the battery, with a battery charger charging the battery when hooked up to mains power.
Many RVs have 3 way fridges that run on gas, 12 volts and 230 volts. Unfortunately these fridges are very power hungry when running on 12 volts, and it is only practical to do so when the engine is running and charging the battery.
An efficient compressor type fridge has a lot lower power consumption, and can be powered by a battery charged by a solar panel. Even so, an 80 watt panel and a big battery is needed, and if you wanted to park longer than 3 - 4 days a second panel may be necessary.
The water pump is used to pump and pressurise water from the water tank under the floor. Because this is not usually running for more than a few minutes it is not really a significant drain on the battery.
TV / Video
The choice here is between a 12 volt TV and a 230 volt TV. The 12 volt TVs range from 10" to 14". They are generally quite a bit more expensive than the 230 volt models but are more efficient than running a 230 volt TV through an inverter. However it may be cheaper to go for a 230 volt TV / Video if you require the inverter anyway to run other appliances.
A separate battery from the starting battery should be used for running the lights and other house loads. The starting battery must have enough charge left in it to start the motor after 3-4 days sitting there, and it is best to not use any power from it to ensure that it is not drained.
The house battery should be a deep cycle type, designed to be discharged all night, and then charged the next day. Even a deep cycle battery will last longer if it is not discharged more than 50%, and this should be our aim when selecting the size of the deep cycle battery. We would aim for enough battery capacity to park for 3 days without sun, and still have the battery less than 50% discharged. Space is usually at a premium in an RV so this may also come into consideration.
If space is very cramped (or for other reasons) it is possible to use the starting battery to run the lights etc, however a reliable low voltage disconnect device should be used to ensure there is enough power left in the battery to start the engine the next morning.
Solar panels start at 1 watt and go up to 120 watts. Factors to consider when deciding which panel to fit on a RV include power requirements, space available, battery size, and of course cost. Some smaller vans simply haven't got room for a big panel, and there's not a lot of suitable space on even the bigger vans, when shading from aerials, vents and skylights is allowed for. However it is usually a case of balancing the power requirements versus what the owner is prepared to spend on solar that decides which panel is used.
A van that is used for the occasional weekend away, and is only running a few lights and a 12 volt TV could be fitted with a 20 to 40 watt panel. This would be enough to keep the battery fairly full for the weekend, and will also provide a charge to top the battery up when not in use. Less than 20 watts and you're really only trickle charging the battery, which is still worth doing, especially if the van is not used often. In this case the starting battery could also be trickle charged.
Battery size would probably be in the 50 - 100 Amp / hour range. More lights, a bigger TV, slightly longer stays, and a 50 to 60 watt panel would be advisable. Battery size would be in the 70 - 130 Amp / hour range.
Most vans that are running a fridge, TV and quite a few other accessories will go for a panel in the 64 watt (Unisolar) to 80 watt range. These systems may also be 24 volt, so 2 x 60 or 80 watt panels may be used. For longer stays a 120 watt or 2 x 64 - 80 watt panels would be advisable. Battery size would probably be in the 130 - 220 Amp / hour range.
Heavyweights (full size coaches) are often full time homes for their owners, and need a power supply to suit. They would probably require a couple of panels, be they 64 watt Unisolar or Kyocera 80 to 120 watts. Battery size should be at least 220 Amp / hours, and the system will probably be 24 volts. 350 Amp / hour battery banks are quite common and there are some larger ones cruising around. Usually they have quite high power requirements and may have a back up generator as well.
To be continued....
That's all for this month folks!
Cheers from Dave and all the RPC crew.
Dave Lambert (Director)
- Issue #92 - 06/12/2005
- Issue #91 - 15/11/2005
- Issue #90 - 20/10/2005
- Issue #89 - 29/09/2005
- Issue #88 - 01/09/2005
- Issue #87 - 29/07/2005
- Issue #86 - 04/07/2005
- Issue #85 - 03/06/2005
- Issue #84 - 05/05/2005
- Issue #83 - 01/04/2005
- Issue #82 - 03/03/2005
- Issue #81 - 23/02/2005
- Issue #80 - 02/02/2005
- Issue #79 - 05/01/2005