DIY powertank - Electrical Diagram

[Physopto]

ah so close ! I need 6 amps

But I see what you mean. A bit easier as I am not good at soldering and such. I'll look into all this, maybe even try my luck at the DC-DC convertors shown above if I get the courage

What takes 6 Amps?

Derek

[Vox45]

What takes 6 Amps?

Derek

That would be the load at maximum for all the devices ... Hmmm that is not how we calculate this ?

[Stub Mandrel]

If you parallel two 12V lead acid batteries that will work fine, but do make sure hey are at a closely similar level of charge/voltage when you actually join them up as any imbalance will cause a large current to flow, and if its big it could damage the batteries or worse.

Once paralleled up successfully best top treat as a single battery and charge them in parallel.

OK to do this with Llithium as well, but not Nicad or NIMH (because of high self-discharge rates leading to imbalances) and DON'T mix two types of cell in one battery.

Voltmeter was right where the diagram shows, across the batteries before the switch with will drain current when the box is switched off.

[Physopto]

That would be the load at maximum for all the devices ... Hmmm that is not how we calculate this ?

That was the point of what I was trying to say, split up the devices between power supplies.

I have three of the devices. One for the camera one for the mount. The other is to be used for the focuser and ancilliary gear.

It is not a good idea to use the same  power supply for the mount and camera. It can cause problems, so why not separate them?

It cost me £40 for the three DC/DC supplies.

There are posts on here talking about this very problem.

Getting anything above 60 watts will be very expensive and counterproductive,  I think.

Derek

[Vox45]

I am leaning more on Alien 13 kind of setup so after a good night sleep it came to me that I don't need to buy the Astronomiser kit for the DSLR as I can add a 12V to 8V convertor/regulator in my panel.

So I revised my design and added 3x 12V convertor/regulator and 1x stepdown 12V / 8V:

1x for my 12V 2.5A powered hub

1x my mount

1x spare

1x for my DSLR 8V 1.5A

Added 3A fuses where I won't use fused cig lighter plugs (I'll change these plugs in a futur design)

[Vox45]

Addition:

As this is mainly to protect my gear, would a Zener diode that limits the voltage to 12v be sufficient ? I would then only need a stepdown to 8V for the DSLR, correct ?

[Vox45]

I did something similar with mine, DC-DC convertors are a good idea if you want to power multiple I tems (usb, camera, 6v mount) I can either use mine with a 12v battery or a 6A mains adaptor in the house and fed outside.

Alan

Ha ! I think I found the ones you are using

[Alien 13]

The only way you could use a zener diode is as part of a crowbar circuit but that would also require a fuse to blow if the circuit went over voltage, it would probably be cheaper to use a convertor.

It could be useful to add some USB power outlets to the design this can be done cheaply by modified off the shelf units in fact my local £ shop has some that include 2 cigar lighter sockets and 2 USB outputs.

Alan

P.S thats them....

[Vox45]

As you bought more than you needed, if you have any spare left I would gladly buy them from you

[Alien 13]

Unfortunately ive used them all up they are so handy.

Alan

[Physopto]

The only problem with step down convertors is they only step down. If the supply voltage goes below about 12.5 volts then the out put  goes below 12 volts, so you can easily go below manufacturers specs for their devices.  If you have a long lead from the battery, under load there will be a larger voltage loss. To compound this even with a short lead, a fully charged lead acid battery is 12.8 volts  at half capacity it's voltage is at 12.4 volts after that the voltage drops off very fast to 10.6 volts fully discharged. So before you have used half the batteries capacity you will find that the voltage to your gear is below 12 volts.

Hence the reason I suggested the DC/DC convertors. Depending upon maker they out put a stable 12.2- 6 volts even when the battery voltage drops to around 11 volts (again dependant upon make, some down to 10 volts).

On a 110 AH battery the step down controller will likely only be able to supply 12 volts to about 30-40% of the battery capacity whilst the DC/DC convertor can out put 12.2-6 volts down to about 70-80% of the batteries capacity. In the cold the situation is worse as battery capacity drops off drastically.

It can make the difference between a whole nights imaging of less than half that. Obviously average  current consumption will affect the individual setups.

Derek

[Vox45]

No problem they are cheap, it's the shipping that cost a lot !

I'll try to find one in my local electronic store...

[Vox45]

The only problem with step down convertors is they only step down. If the supply voltage goes below about 12.5 volts then the out put  goes below 12 volts, so you can easily go below manufacturers specs for their devices.  If you have a long lead from the battery, under load there will be a larger voltage loss. To compound this even with a short lead, a fully charged lead acid battery is 12.8 volts  at half capacity it's voltage is at 12.4 volts after that the voltage drops off very fast to 10.6 volts fully discharged. So before you have used half the batteries capacity you will find that the voltage to your gear is below 12 volts.

Hence the reason I suggested the DC/DC convertors. Depending upon maker they out put a stable 12.2- 6 volts even when the battery voltage drops to around 11 volts (again dependant upon make, some down to 10 volts).

On a 110 AH battery the step down controller will likely only be able to supply 12 volts to about 30-40% of the battery capacity whilst the DC/DC convertor can out put 12.2-6 volts down to about 70-80% of the batteries capacity. In the cold the situation is worse as battery capacity drops off drastically.

It can make the difference between a whole nights imaging of less than half that. Obviously average  current consumption will affect the individual setups.

Derek

I see.

I think that the DC/DC stepdown convertor is what I need for the 8V DSLR.

But I was wondering about what should go on the other connectors that need a standard 12V output... You answer that, although the convertor you linked does not suits my need, I would prefer to have the same type as Alien 13 linked so I can mount them inside a small my power panel.

I did see regulators but they all say that the input voltage has to be higher than the output voltage, so if my 12V input drops to 11V as you described than they can't output 12V

What am I missing here ?

[Alien 13]

Regulators/dc-dc convertors allways need a slightly higher input/output voltage to operate so for the camera they are ideal any items requiring a nominal 12V can run directly off a battery or if you want some extra protection then another convertor.

Most Items that are connected will have inbuilt dc-dc convertors/regulators to maintain correct opperation but can sometimes be damaged by overvolts so having convertors you could be operating you kit at the same time the battery is charging.

If the battery drops much below 12v then the regulators will stop functioning but by this point the battery is past its useful life anyway and should be recharged.

Alan

P.S Amazon used to do dc-dc convertors at a reasonable price.

[Physopto]

DC/DC converters of the type I suggested will put out a regulated 12.2-6 volts almost regardless of input between about 10-11volts up to 16volts input. So what you need. I have to go out now but I will post a bit more later on

Derek

[Vox45]

Regulators/dc-dc convertors allways need a slightly higher input/output voltage to operate so for the camera they are ideal any items requiring a nominal 12V can run directly off a battery or if you want some extra protection then another convertor.

Most Items that are connected will have inbuilt dc-dc convertors/regulators to maintain correct opperation but can sometimes be damaged by overvolts so having convertors you could be operating you kit at the same time the battery is charging.

If the battery drops much below 12v then the regulators will stop functioning but by this point the battery is past its useful life anyway and should be recharged.

Alan

P.S Amazon used to do dc-dc convertors at a reasonable price.

I'm mostly concerned about the mount of course (HEQ5) it should contain an inbuilt DC-DC convertor you say ? I'll look into this

As I will not charge while operating my gear, the idea is to protect from overvoltage the 12V devices and use a single stepdown for the DSLR. You talked about crowbar and I see that there are things called varistor... if it's too complicated then I'll stick to what you both say and use DC-DC convertors

I have to take the plunge at some point

[Alien 13]

If you are only ever running from a standard battery then direct fused connections will be fine and a DC-DC convertor for the camera.

The addition of a voltmeter to check the battery condition and maybe a LED indicator for power on is all you need, look forward to seeing the finished product.

Alan

[Vox45]

Got my shopping list ready wondering if an Ampmeter would serve any purpose (I never see those on other DIY projects.... for a reason I assume) and a small fan ?

I'll post pictures and hopefully not pictures of my gear on fire ...

[Physopto]

DC/DC converters of the type I suggested will put out a regulated 12.2-6 volts almost regardless of input between about 10-11volts up to 16volts input. So what you need. I have to go out now but I will post a bit more later on

Derek

Hi,

As I said above the DC/DC convertor regulator is my preferred option. It will ensure that you get between 12.2 to 12.6 volts output to your equipment regardless of input voltages between around 10/11 volts up to about 16 volts, depending upon maker. The Huntersfield devices are good. They were originally manufactured for the caravan/motorhome market, for 12 volt TVs. These 12 volt TVs don't like any voltages above 12.6 volts and if it exceeds this they usually fail at some point,(sooner than later).

I suggest that you look at the specs for your EQ5 mount. I think it will state that it will work between 11 and 14/15 volts. But a CCD camera usually has a lower upper voltage threshold. My QSI is stipulated at 14 volts. Above that it alarms but I have found it also shuts down, requiring a full shut down of controlling software (MaximDL) and disconnecting power to the CCD. It caused me all sorts of delays and loss of imaging time.

To get the 8 volts you want I suggest that you use the same DC/DC convertor and then put the 12.2-6 volt output through the stepdown device to get to 8 volts. This will ensure that it always gets a stable regulated voltage. Varistors and zenner diodes are not a good option unless you know exactly what you are doing.  Varistors loose a lot of power as heat. I haven't used zenner diodes for many years so don't know what is available now.

By doing it this way you should be assured of close control of you voltages to the equipment and separating one device from another, especially the CCD/camera from the mount.

Also you will be able to get the correct  regulated voltages to the equipment  even when the battery voltage drops to around  11 volts or so. At that voltage the battery is in effect almost flat anyway.

A benefit is also that you can safely charge the battery all the time with out affecting any of your gear, so in effect the battery will have a much extended lifetime. Even leisure batteries will loose storage capacity over time even if only slightly discharged. Again another advantage is you could use a car battery as it is never discharged.

I hope this helps you to decide.

Derek

[Vox45]

Thanks to both of you guys for taking the time to help me on this project.

I learned a lot from your explanations and feel I am ready to start buying the different pieces and start building this So far, I added the cost of everything and I am coming close to 130€ which is not bad for something that perfectly better suits my needs not counting the money I DON'T have to spend on the DSLR battery ... If I ever come to a star party in the UK and meet you, the beer is on me

I'll post pictures as I go along ...

[Snaxmuppet]

I have huge respect for you Vox45 and others that build their own kit this way. I have just bought an imaging set up and I am looking at how to power it all at this moment (hence me reading this thread) and I wouldn't dream of building something like this myself. I have less than zero DIY skills and have to build myself up for weeks just to put up a picture on the wall!

I am trying to find a tried and tested way to power a full imaging set up all night and I am struggling. I love the idea of a Power Panel but at those prices I think I will continue my search.

As a newbie to astronomy I am a bit surprised that there is not a well-tried and tested commercial solution. There are the Powertanks but they are really just rebadged car starter packs and so they generally don't have a big enough battery (17Ah is typical) and in any case the battery they supply is not a deep discharge type and so isn't really suitable.

You guys inspire me into thinking I might be able to build something myself... I already have sweaty palms

[Vox45]

Don't worry I am just like you and it took me a lot of reading and asking a lot of questions to get to a point where I feel confident enough to do this. The end result will be ugly but that's not really a problem. My main concern is to not set my house on fire

But I think that once you understand what you are doing, have had a lot of discussions and approval on the project from mentors then you can safely take the plunge

As for a tested commercial solution you can take a look at this

They are a bit expensive but not that much for the quality of each parts that are used to build those (notice the hub that they use seems to be a Startech hub!)

Here are the parts I will be using to do this. Most are less than 3£.

1x 15A Resettable Circuit Breaker

2x 3A Resettable Circuit Breaker
2m of 15A wire
2x distribution bloc

1x XLR connector
1x DC/DC Stepdown 8V
1x DC/DC 12V to 12V
1x 12V Fan (maybe.... not sure if needed)

1x voltage indicator
2x marine cig lighter female

1x on/off switch

1x project box (around 7£)

1x Startech USB Hub (around 50£)

A bit of soldering (I'll try to have a friend do this for me) and a bit of drilling in ABS plastic the rest is just following the diagram I posted and fitting this in a box ...

I will be a bit nervous at 'First Power On' but I do have a voltmeter so I can mesure the output of everything BEFORE pluging my equipement.

[RLWP]

You could use crimp connectors instead of soldering

Richard

[Vox45]

I'll try to do as less soldering as possible I would thing that I won't be able to avoid it on the DC/DC regulator and stepdown modules (?)

[RLWP]

I'll try to do as less soldering as possible I would thing that I won't be able to avoid it on the DC/DC regulator and stepdown modules (?)

That's fair enough. You can still do a lot of the rest with crimps. I use them for all the boat engine wiring that I do

Richard