12v battery. voltage regulator required?

[abhoriel]

I've been using a 12v leisure battery to power all my equipment: HEQ5 mount, DIY dew heaters. It will soon be powering my raspberry pi (and other USB powered devices) and my recently acquired CCD. 

I used to use a laptop for imaging, and I had a 90W 12v adapter to charge it, but on long cold nights this would cause the battery voltage to drop below 12v and actually caused problems when the mount was slewing. In hindsight, getting a 90w adapter was stupid, I should have gone for a lower power one.. Anyway, another astrophotographer has recommended I use a 12v voltage regulator to prevent voltage drops from damaging my equipment. Do other people use voltage regulators with their 12v batteries?

 

[ronin]

If you have a 12 regulator in line, you can easily build one, then the voltage into it needs to be around 15 volts. You need 2 or 3 volts more then the regulated output. One would work OK on my 9v scope as I would start with 12v and regulate it to 9v, but if I start with 12v and add a 12v regulator I thing I would get about 10v out. I do not think a regulator will mean it never drops below 12v just it does not go above 12v.

Part of the problem is that the regulator takes some of the power from the battery to do it's job.

Your leisure battery is likely to be around 13v but I would guess that to get 12v out you need more the 13v in. And still think it will allow the voltage to drop below 12v if the battery output drops.

[Gina]

Am I right in assuming that you charge up the battery indoors (or near a mains source) and then take it out to your imaging sight, which has no mains electricity supply?  If so you would really need a larger capacity battery to last the night with the load you have on it.  OTOH if you go over to RPi for your image capture and equipment control, your working load will go down enormously and the present battery will power your mount for much longer.

I'm in the process of writing a tutorial for setting up a Raspberry Pi which may be of help :-
Tutorial :- Setting up a Raspberry Pi for Astro Imaging and Hardware Control

[RayD]

I agree, a voltage regulator isn't really going to do anything with a battery output, it's effectively already regulated @2.1v per cell by it's design.  As Ronin notes, a regulator is there to pull the voltage down to the preset level from a higher one, and keep it there irrspetive of what the input voltage is doing.  It's not to limit it from dropping further. 

Note a fully charged "leisure" type SLA battery off load is 12.6v.  You will charge it at around 13.7 - 14.6 or so depending on the type of battery and stage of charge.  In theory a leisure battery will discharge to an 80% depth of discharge without permanent damage, which means it will actually handle discharges to 10.1v.  Of course apart from not being ideal for the well being of your battery, this low voltage is not going to suit your equipment, some of which needs the upper end of 12v to operate correctly.  It's precisely this reason that many regulated power supplies are actually 13.8v (look at the FLO Nevada one), as this is the upper limit of many 12v voltage regulators.  In fact SW suggests 13.8v as ideal for the AZ-EQ6 as it reduces the current, thus the heat.

In short, if your 12v battery when fully charged is then dropping below 12v on load, it is either not adequately rated for the load you have on it, or it has reached the end of its life and isn't holding its charge.

You don't actually note what size your battery is, but I would agree with Gina's suggestion that it sounds like you simply need a bigger battery as it does sound like you have a few things coming off it.

Once you start loading a battery up, even with relatively small total loads at say 6.0A, you'd be surprised how quickly they discharge.  However, fortunately for us we can apply deration, which means not all the kit is on full power all the time, but it still doesn't take long to deplete a small battery.  As an example, if your total nameplate equipment load adds up to 6A, you can safely assume a constant load of 3A as you will most likely be operating at no more than around half the time at full load, or no more than half the load all the time.  For example your mount is only on full load when out of balance and slewing at maximum speed etc. Apart from this, when tracking, it actually draws very little load.  Also your filter wheel is only on load when moving, otherwise power consumption is nominal.  With my kit the only exception to this 50% rule of thumb is my CCD, which is around 60-70% if I'm using cooling, but is countered by the rest.  This isn't an exact science by any means, but is my current assessment based on all my equipment, its usage, and quoted power output.  For me so far this has worked out pretty well spot on.

Just to give you an idea, I have a 33AH battery running my kit on drive-out sessions, including mount, cameras, filter wheel and heaters etc. and I can get a full night from that, but will need to charge it again for a second full night.

[SonnyE]

I use a large Leisure battery (an AGM 12 volt 53 pound baby) to run my mount and CCD cooling. I don't run dew heaters. Were I to run them, I would do so on a mains power supply separate from my mounts needs.

Would it be possible to separate your loads? I'm suggesting a second battery for the dew heaters, while keeping your voltage/power critical loads separate.

Thus, if you lose power to your heaters, it's not a big deal. But getting into a critical voltage with your mount and it's motors could really spoil the fun. (Ie: burned out motors, fried electronics)

Edit in: Like a bigger, newer battery, and use it for your critical loads, while using the older battery for the heaters.

[abhoriel]

The issue was that the battery was being overloaded I believe, I dont think I've managed to destroy it yet! (I always keep it charged and haven't deeply discharged it yet). The voltage went back up to well over 12v once the laptop charger was disconnected. Its a 12v 55Ah battery. I have a smart charger which I leave it connected to whenever its not in use. I think it should be adequate if I don't use the laptop charger! Anyway, yeah I don't know how voltage regulators work. If they work by regulating a higher voltage input to a lower voltage output then it wouldn't help in my situation anyway!

I'm working on getting the raspberry pi working currently, a major reason being the lower power use and I also don't really like leaving laptops around outside with the frost and dew. The weather is generally awful so I'm testing indoors. The raspberry pi with Indi is quite interesting. I'm trying to get local platesolving set up currently, and need to decide whether I guide with phd2 or using Ekos' own guider.

Separating the loads is a good idea. Especially as the dew heater controller I'm about to build uses PWM to control the heat... Those relatively high currents turning on and off are are a concern for causing interference.

 

Thanks a lot for the responses. I will check out the RPi tutorial as well Gina!

[RayD]

Yes definitely very good advice from SonnyE to separate supplies for heaters if possible, especially if you are looking at PWM controller.  Laptop chargers are a known killer for 12v batteries.

55AH is more than enough for a night's viewing so you're pretty much there