Article (Equipment and Software):
Refuting DC-DC Converters as a Solution to Voltage
In the past, I have fully endorsed the use of DC-DC Converters as a solution to voltage when powering numerous pieces of equipment from a single Marine Deep Cycle 12 V battery. The motivation was simple. It is common that connecting a mount as well as a CCD camera to a single battery causes a significant voltage drop that can at times hinder performance. For example, people commonly find this with their mounts having the power LED flashing. A solution that has been commonly employed, and admittedly one I have endorsed in the past, is to place a simple DC-DC Converter between the battery and the piece of equipment (normally the mount or CCD camera). A simple one such as this one:
The above is the infamous Universal Laptop Car Charger that being universal, has an output voltage setting. This is excellent for a mount as for example, the Skywatcher NEQ6 Pro and the Avalon M-Uno, both of which I have owned, are happy to operate on up to 15 V. Setting 15 V on this then ensures that no matter the output voltage of the battery (subject to a certain minimum!), the mount receives a clean 15 V that is also regulated to stay at 15 V. This seems to side-skirt the issue of the CCD camera causing the drop in voltage across the mount that yields patchy tracking (power LED flashing). A more sophisticated version of the above is something like the following:
This is essentially the exact same thing - a DC-DC Converter but with a variable resistor to set the output voltage. This particular one allows an output voltage between 12.5 V and 35 V, which is excellent for CCD cameras as they tend to not like voltages as high as 15 V and prefer to work below 14 V but above 12 V.
QSI however advise that use of DC-DC Converters simply masks an underlying issue of ground loop in the electronics. The underlying issue is what most astrophotographers running their equipment from batteries seem to do - daisy-chain equipment with two- or three-way 12 V plug adapters on to the battery. The problem here is that multiple pieces of equipment share a positive and negative connection under a single cable (typically from the two- or three-way adapter down to the battery). QSI instead advise having a completely separate power cable for each piece of equipment and making sure the cabling used is of sufficient thickness (gauge) to yield close to no voltage drop over certain lengths. They specifically recommended 18 AWG (1.024 mm) cabling for up to 1.8 metres or 16 AWG (1.291 mm) for longer cabling, up to a certain limit which I assume to be about 2.5 metres or so.
When I used to use my battery to power my equipment, I went a step further and simply bought 2.0 mm cabling, which is about 12 AWG. I decided to do away with the standard 12 V plugs and just go straight from the battery on to the equipment so I had Copper crocodile clips soldered on to one end of the cables for clamping on to the battery terminals. On the other end, I attached some really good 2.1 x 5.5 x 10 mm DC power plugs I bought from eBay:
QSI however advise that use of DC-DC Converters simply masks an underlying issue of ground loop in the electronics. The underlying issue is what most astrophotographers running their equipment from batteries seem to do - daisy-chain equipment with two- or three-way 12 V plug adapters on to the battery. The problem here is that multiple pieces of equipment share a positive and negative connection under a single cable (typically from the two- or three-way adapter down to the battery). QSI instead advise having a completely separate power cable for each piece of equipment and making sure the cabling used is of sufficient thickness (gauge) to yield close to no voltage drop over certain lengths. They specifically recommended 18 AWG (1.024 mm) cabling for up to 1.8 metres or 16 AWG (1.291 mm) for longer cabling, up to a certain limit which I assume to be about 2.5 metres or so.
When I used to use my battery to power my equipment, I went a step further and simply bought 2.0 mm cabling, which is about 12 AWG. I decided to do away with the standard 12 V plugs and just go straight from the battery on to the equipment so I had Copper crocodile clips soldered on to one end of the cables for clamping on to the battery terminals. On the other end, I attached some really good 2.1 x 5.5 x 10 mm DC power plugs I bought from eBay:
As an extra measure, I bought a pair of Ferrite cores from eBay and placed them near the DC power plugs on both cables. Both cables are cut to the minimum length I need them to be, with a little bit extra for maneuvering (about 1.6 metres each, for the mount and the CCD camera). Given the wire thickness, the short length, the straight connection from battery terminals to the equipment and the Ferrite cores, these cables were bound to work well.
In summary, they did. They worked extremely well actually. My 85 Ah Marine Deep Cycle battery had been charged about two weeks prior to testing these cables and was reading 12.71 V straight from the terminals. I connected both power cables to it like so:
In summary, they did. They worked extremely well actually. My 85 Ah Marine Deep Cycle battery had been charged about two weeks prior to testing these cables and was reading 12.71 V straight from the terminals. I connected both power cables to it like so:
I tested the mount slewing and tracking while the CCD camera was being continuously cooled to -10°C (from an ambient temperature of about 30°C!) and exposing and everything worked flawlessly. The CCD camera did not complain at any point (QSI cameras have an LED and internal speaker to report low or high operating voltage) and the power LED on the mount was solid (no flashing). All of this without a single DC-DC Converter in the circuit, and no two- or three-way adapter of any kind.
Ultimately, it seems to me the best solution to stable voltages with a Marine Deep Cycle 12 V battery is:
Ultimately, it seems to me the best solution to stable voltages with a Marine Deep Cycle 12 V battery is:
- Build your own power cables from thick cabling, ideally running straight from the battery terminals into the equipment. 2.0 mm cabling (12 AWG) works excellently for most common lengths up to around 3 metres though the shorter, the better. Make sure the clips for the battery terminals are of high quality and that the DC power plugs fit your equipment well (most equipment use 2.1 x 5.5 x 10 mm DC power plugs, which are easy to source). You may wish to place a Ferrite core in a small loop just before your DC power plug to reduce interference. You may also wish to place an in-line fuse holder with a fuse within the positive wire of your power cables if you want to fuse your equipment.
- Connect your power cables straight into the battery terminals without any common cabling for any piece of equipment that requires a good voltage (e.g. mounts and CCD cameras). Do not use two- or three-way adapters. Avoiding any kind of daisy-chaining.
- Give your battery a good charge prior to use and verify the voltage is good using a multimeter. Generally if your battery terminals read above 12.5 V after the charge, it is good to go. Mine always read about 12.9 V after it received a good charge over-night.
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