6v lead-acid battery to drive Celestron Omni CG-4 mount?

[jonathan]

Having been using 4xAA batteries for a while now with my CG-4 I thought it might be time to step it up a notch and try using a proper battery that should last better and be easier to manage, I couldn't see any downside to it really as the original spec of 4xD cell should be the same as 1 x 6v Lead-acid, right?  It is a 4Ah small sealed lead-acid battery from Yuasa, their blurb states that it should be good for cyclic use, I purchased a specific charger for it as well (Ansmann).

Could there be any problems with using such a setup?  I plan to hold the battery in a compact camera case which I will hang from the tripod (upright), I have made a set of power cables with easy-release plugs in case of snagging and for easy charging, just have to sort out an in-line fuse (thinking along the lines of an auto blade type fuse holder, not sure which fuse I would need yet though for burst motor drive - some forums reckon as much as 3.5 amps when driving the Dec or Ra at 8x).  I might remove the Dec motor and just use slow-motion control knob, let the Ra do the work and learn better polar alignment (I fitted a polar scope but since it's been summer I haven't had much chance to practice).

I keep reading about how many Ah four or five AA or D rechargeable batteries have, it sounds like a lot!  How is it that such a small set of batteries can have more Ah than a big lead-acid battery?  I might try the 5-AA battery pack concept as well, as I think I may have under-voltage with just four (1.2v each) which is throwing out the tracking a bit.

The thing that prompted me to use AAs in the first place instead of D cells is that I could not find out the actual capacity of any of the D cells I could buy off the shelf, and rechargeable D cells seem non-existent.  I read from multiple sources that most C and D cells were just AA cells in a C or D cell package so there was no actual benefit to having a bigger, heavier battery, and I can actually believe that to be true from the lack of information about capacity for D cells.  Quite a few rechargeable AA batteries have bogus (optimistic) Ah ratings anyway, it all seems a huge mine field, making a simple 6v 4Ah lead-acid battery seem a good choice.

Typically I would not observe for longer than three hours, so if I manage to use up 4Ah in that time with (from what I read) 0.4Ah in tracking and the rest in burst slewing (homing in on the target after manual slewing off the clutches) then I'm fine with that.

[ronin]

Roughly how much were you intending or expecting to pay for the battery?

The battery you describe will I guess be a 6v motor cycle battery and when I had my bike I was replacing the battery at regular intervals, when it drained I needed a new one and it drained often and quick.

If you were OK with a soldering iron I would suggest a 12v Li-ion and make a simple regulator to go inline.

I have a 12v tracer for a 9v scope and fortunately Tracer supply an output cable that is a car connector and I have a Maplin unit that plugs in and is switchable from 12v to 1.5v. Tracers are not inexpensive and there is a 12v rechargeable thjat is more basic but less: EBay-Li-ion

I will get one and make a 9v regulator for one eventually.

Couple of 6v Li-Po around but one is in the US and the distributor here does not do them.

Finally, the reason i asked about expenditure, is this one: BM-Li

But it seems costly, and not sure if a normal charger will be OK, think some I have read say they are, but check asn having one go bang is not a good idea.

[Alien 13]

I dont know how similar your mount is to an EQ3-2 but I have been running mine off a simple 5V power bank its 12Ah and cost me less than £10, I did originally have reservations about it only being 5V but it does seem to work fine.

Alan

[David Smith]

My D Cells seem to last pretty well. My drives came with a set of "partially discharged" D cells so I bought a brand new set of Duracells but the set that came with the drives are still going! I think I read some where that a decent set of D's should last about 20 hours but mine have far exceeded that and that's with a lot of slewing at 8x and they were part worn. I was thinking longer term of an alternative power source but may not need it.

Do you know the polarity for the dc input socket on the hand box?

Thanks

[Bizibilder]

I use a 6v lead acid with my EQ5 and have had no trouble with it at all.  It will run for at least 3+ hours.  I'm pretty sure I bought a 4Ah battery.  I just keep it charged and have had it in regular use for about three years now.  It is most often used for winter Sun photography and is stored indoors at normal room temperature for the rest of the time.

[Lonestar70]

Having been using 4xAA batteries for a while now with my CG-4 I thought it might be time to step it up a notch and try using a proper battery that should last better and be easier to manage, I couldn't see any downside to it really as the original spec of 4xD cell should be the same as 1 x 6v Lead-acid, right?  It is a 4Ah small sealed lead-acid battery from Yuasa, their blurb states that it should be good for cyclic use, I purchased a specific charger for it as well (Ansmann).

Could there be any problems with using such a setup?  I plan to hold the battery in a compact camera case which I will hang from the tripod (upright), I have made a set of power cables with easy-release plugs in case of snagging and for easy charging, just have to sort out an in-line fuse (thinking along the lines of an auto blade type fuse holder, not sure which fuse I would need yet though for burst motor drive - some forums reckon as much as 3.5 amps when driving the Dec or Ra at 8x).  I might remove the Dec motor and just use slow-motion control knob, let the Ra do the work and learn better polar alignment (I fitted a polar scope but since it's been summer I haven't had much chance to practice).

I keep reading about how many Ah four or five AA or D rechargeable batteries have, it sounds like a lot!  How is it that such a small set of batteries can have more Ah than a big lead-acid battery?  I might try the 5-AA battery pack concept as well, as I think I may have under-voltage with just four (1.2v each) which is throwing out the tracking a bit.

The thing that prompted me to use AAs in the first place instead of D cells is that I could not find out the actual capacity of any of the D cells I could buy off the shelf, and rechargeable D cells seem non-existent.  I read from multiple sources that most C and D cells were just AA cells in a C or D cell package so there was no actual benefit to having a bigger, heavier battery, and I can actually believe that to be true from the lack of information about capacity for D cells.  Quite a few rechargeable AA batteries have bogus (optimistic) Ah ratings anyway, it all seems a huge mine field, making a simple 6v 4Ah lead-acid battery seem a good choice.

Typically I would not observe for longer than three hours, so if I manage to use up 4Ah in that time with (from what I read) 0.4Ah in tracking and the rest in burst slewing (homing in on the target after manual slewing off the clutches) then I'm fine with that.

Hi Jonathan,

Plenty of data on rechargeable D cells here: -

http://www.componentshop.co.uk/d-size-10000mah-nimh-battery-single-battery.html?___SID=U

And I can assure you D cells are not AA cells in a different body... they can supply much higher instant current than an AA cell and also can be obtained in up to 10Ah rating.

The only problem with rechargeables is the 1.2v cell voltage so you would need 5 to achieve a nominal 6v.

As for your Yuasu 4 Ah Battery... be aware that the stated 4 Ah rating is at a discharge rate of 1/20 x C... which is 200ma.

This capacity drops if the battery is discharged at a higher rate... e.g. if you discharge at 1/10 x C (400ma) the 4 Ah rating falls to 3.7Ah.

The other issue is working temperature... the above Ah capacity figures are at 25 deg C... this will fall considerably at 0 deg C or lower.

I would say that you would at best get 2 hours use from a 4 Ah battery in the cold of night before it discharged to the minimum recommended voltage of 1.75v per cell... (a 6v battery has 3 cells so 5.25v) if you discharge below this you will damage the battery.

You would probably be better of with a higher Ah SLA... say 10 or 12 Ah.

Lithium batteries have good capacity even at low temperatures but are much more demanding about minimum voltage and charging regimes... they are also considerably more expensive... as are proper chargers for them.

I attach the Yuasu data sheet for the battery you are looking at... take a look at the discharge curves which will show you the times at different discharge rates.

I hope this is of some help.

Best regards.

Sandy.

AMP9218_UK.pdf

[jonathan]

I do already have the 6v Yuasa battery, all wired up and ready to go (minus inline fuse), a brief test showed the controller unit seemed happy, slewing worked as did tracking, although this was all done indoors with nothing attached to the mount.

I am just afraid of burning something out by not using the specified D cells, if it turns out that the battery doesn't last long enough or can't handle the cyclic use then fair enough, I will look at other options, I just didn't like the original battery pack (a pain to replace the batteries in) and wanted to avoid having a big heavy 12v high capacity battery or mains supply.

[jonathan]

Do you know the polarity for the dc input socket on the hand box?

Thanks

I believe it is tip positive.  Just trace the positive connection from the battery box back to the controller if you're unsure.

[Lonestar70]

I do already have the 6v Yuasa battery, all wired up and ready to go (minus inline fuse), a brief test showed the controller unit seemed happy, slewing worked as did tracking, although this was all done indoors with nothing attached to the mount.

I am just afraid of burning something out by not using the specified D cells, if it turns out that the battery doesn't last long enough or can't handle the cyclic use then fair enough, I will look at other options, I just didn't like the original battery pack (a pain to replace the batteries in) and wanted to avoid having a big heavy 12v high capacity battery or mains supply.

Hi Jonathan,

You will not do any damage to your mount using a 6v 4Ah SLA battery, just fit a suitable in line fuse in the feed cable, say 3.5amp or 5 amp and be absolutely sure you have the tip polarity correct.

The mount will only draw the current it needs, regardless of the battery type and remember to recharge the battery after each use with a good quality charger.

If you decide to change to D cell batteries then a set of 5 x 10,000mAh rechargable D cells (as shown in the link I posted) would give you a 6v 10Ah battery which should last a good few hours.

Good luck and clear skies.

Sandy.

[jonathan]

Thank you, Lonestar. 

Had bad experience with Vapex batteries, I might look up Eneloop D cells and a better D cell holder, thank you again for the info.

[jonathan]

Looks like Eneloop D cells are just four AA cells in a D cell wrapper, better than just a single AA cell like I've read about in some places but still lacking in potential power for the size of it (only around 6,000 mAh).

Could not seem to find the Accupower batteries, plenty of expensive chargers under that name but no D cells.

The Powerex 11,000 mAh batteries look more promising - http://www.mahaenergy.com/powerex-d-11000mah-2-pack/

I have an AA size intelligent charger with discharge and cycling modes etc so should be able to use some AAA - AA converters wired up to D cell battery holders as described here in order to charge the 11,000 mAh D cells.

[jonathan]

I have put a 2A quick blow fuse in the in-line fuse holder, runs the mount on 8x slewing (both motors simultaneously).  I have a variety of fuse ratings to go at in case the current draw becomes higher with heavy loads but I'm optimistic that 2A should be fine.  The wiring is probably only good for about 6A anyway so 2A - 3A gives me a good margin.

Just need a cheap camera case to hold the battery now, one that I can hook onto the tripod somewhere.  Been looking in the cheap shops but nothing so far, just a compact camera one should do so long as it fits the battery.  Online shopping, here I come.