Tracer battery to power mount

[djpaul]

I'm looking to buy a tracer battery pack to power my Skywatcher az gti mount.

Can anyone tell me if the cheaper 4ah model would be sufficient for a nights observing.

 

[Pig]

Paul..... if your mount / kit draws 1amp hour, it will last for 4 hours...... half an amp 8 hours,  and so on ?

[djpaul]

5 minutes ago, Pig said:

Paul..... if your mount / kit draws 1amp hour, it will last for 4 hours...... half an amp 8 hours,  and so on ?

Cheers i will have to what the az gti draws.

[Pig]

1 minute ago, djpaul said:

Cheers i will have to what the az gti draws.

Yes, that would be the first step, there is normally a label on them somewhere that will tell you ?

[djpaul]

I think it draws 0.75A 

[Pig]

Ok that’s 5.33 hours ? so it is ok for a session, but not an all-nighter....... it also depends on how much slewing you do with the scope.

[djpaul]

So I should get 5 hours on a full charge.

[djpaul]

Sounds good enough so that's on my list to purchase at P.A.S.next month.?

 

[djpaul]

Mmm might go for the 8ah. .

That's 10 hours ?

[Pig]

Yes, I can see why. They may also have several ports to enable dew heaters etc...... so having some spare miles in the tank sounds sensible ?

[Carbon Brush]

Hi Paul.

Although not familiar with the mount, I would err on the side of caution.

While tracking, the mount will not use a lot of power. But when slewing it will use more.

So when tracking, the mount will run all night. But if are hopping around, you might be off to bed earlier.

Really you need to measure the current draw for yourself, not rely on a label, to get an estimate of run time.

Also lithium packs tend to give an amp-hour rating based on a specific discharge condition. That being a constant current at a particulalr temperature.
Move away from these parameters and capacity is lower.

Having said all that. What happens when you make your next astro buy and it takes power from the same pack?

As you are looking at a lithium pack, the situation is different to the (primitive) lead acid power packs that fade away from the date of manufacture.
Lithium packs tend to gradually lose capacity based on the number of charge/discharge cycles, and depth of discharge.
Think of 3 years of use nightly to go to 2/3 of original capacity.
The time related degradation is far less important than for lead acid.
This means buying in extra capacity for the future is not wasted in the way it is for lead acid.

In your position I would be tempted to dig a little deeper into my pocket and go up on size.
Just how much depends on the current measurements.

 

[djpaul]

I go have a good friend that has offered to sell me his tracer 16ah.

Not sure if it's an older tracer model it's bigger and orange in colour rather than the slim black ones .

[Pig]

It’s always a bit risky getting secondhand powerpacks, mainly due to not knowing how they have been looked after. Also consider the charging time with 16ah Paul, they can take some time to charge.

[djpaul]

Charging time would be okay as I will charge it over night or during the day I need it.

I know the guy well and he really looks after his kit.

They retail at £275.

Could take his one for the same price of the 7ah new. 

 

[Davey-T]

49 minutes ago, djpaul said:

I go have a good friend that has offered to sell me his tracer 16ah.

Not sure if it's an older tracer model it's bigger and orange in colour rather than the slim black ones .

The orange 16ah is around £50.00 dearer than the grey 16ah one for some reason.

Dave

[djpaul]

I could buy his for £120 ?

[johngm]

I have just been on the Tracer website the LifePo 12AH battery is £167 with the VAT 1400+ Charges or the 7AH version £144.

https://www.tracerpower.com/tracer-12v-12ah-lifepo4-battery.html

 

John

[AbsolutelyN]

I have the 7ah and the az gti. It's a great battery but it's pushing it for a full winter night. I've now hooked up regulated dc supply but if I was to buy another tracer I'd be looking at a much more powerful one as now need to power cooled camera, focuser, dew heaters etc which I did not have or anticipate when I bought the tracer. If it was for powering mount only for half a night at a time I'd say the 7ah is perfect. Handles freezing temps very well.

[Carbon Brush]

Paul.

I would not worry unduly about buying a used Tracer power pack. The inbuilt overcharge and over discharge protection means you cannot harm them in normal use.

I would try to get a feel for how many cycles it has been put through.

If you take the 1400 cycles as correct, that equates to 2800 cycles of half discharge. In general lithium life can be approximately calculated in this way.

Don't forget you can set the charger and walk away. When full charge is measured (not timed) after 4-6 hours with the supplied charger, it switches off.

Lithium out performs lead acid and NiCd/NiMH when there is frost on the ground.

David.

 

[djpaul]

Well I have done a massive deal with my friend and buying a boxed 2 x 2 inch powermate which i have wanted for sometime. and a tracer 16ah battery . Which has only been used approx 20 times for a good price. 

Basically the cost of a new 2 inch powermate.

 

[cletrac1922]

5 hours ago, djpaul said:

I'm looking to buy a tracer battery pack to power my Skywatcher az gti mount.

Can anyone tell me if the cheaper 4ah model would be sufficient for a nights observing.

 

Alternate solution

I use a car jump start battery to power my ED80 on EQ5 mount

Been to astronomy festivals, and has run my mount for over a week, without recharging

Handy to have in shed, if one morning car will not star either

I leave mine on charge when not been used

John

 

[djpaul]

29 minutes ago, djpaul said:

Well I have done a massive deal with my friend and buying a boxed 2 x 2 inch powermate which i have wanted for sometime. and a tracer 16ah battery . Which has only been used approx 20 times for a good price. 

Basically the cost of a new 2 inch powermate.

 

I've done a deal with a friend now. 

[noah4x4]

Tracer batteries are excellent. I have a 24Ah and 8Ah. Why an 8Ah? It is because anything larger and it cannot be taken on an aircraft with my 'grab & go' SE4. . It's 12v x 8A = 96 watts. The typical airline limit is 100 watts.

That leads me to an important consideration. The amp-hours rating of batteries can be misleading. Even with a quality brand like Tracer what matters most is its watt hours capacity and hence the watts consumed per hour (watt hours) by the device. Many battery manufacturers don't state their watt hours. But the power demands of a telescope depend on what it is doing. Think of it just like a car using more fuel when accelerating uphill. Heavy repeated slewing will deplete a battery faster than tracking.

My Evolution mount demands only 9.6v but seeks almost 2 amps when slewing.  Don't panic if you support an Evolution with a 12v battery or AC/DC supply as it will be fine and within tolerance if the amps are sufficient.  But other mounts might demand perhaps 12 volts and 1 amp. The 12v rating of a battery also tends to be notional. For example, a fully charged 7Ah Tracer outputs 13.2 volts. When down to 20% capacity it outputs 12.9v. Only when below 20% does it level out at 12v and eventually fall to 10V (before which most scopes will cut out). These are the manufacturers claimed ratings. 

A 7aH Tracer offers 84 watt-hours. On the manufacturers website it shows its typical discharge curve. If the device requires 50 watts the runtime will be as low as 1 hour 40 minutes.  If the device requires 12 watts when tracking (say 12v x 1A = 12W) it will run for 84/12 = 7 hours. However, when slewing the demand might be 12v x 2A = 24 watts, hence 84/24 = 3.7 hours.  

My recommendation would be to get TWO x 8Ah given that ONE (only) is under aircraft limit and two will suffice for an all nighter at a local dark sky site. If your scope was a Nexstar SE it would run on its AA batteries during changeover. But at home, I need a 24Ah as it runs my camera (20 watts), focuser (10 watts) and Intel NUC (peak 50 watts), hence up to 80 watts per hour (average about 60 watts), and my mount uses its own internal power supply. Power needs to be carefully calculated, especially if required to support more than a mere mount. 

 

 

[cletrac1922]

41 minutes ago, noah4x4 said:

Tracer batteries are excellent. I have a 24Ah and 8Ah. Why an 8Ah? It is because anything larger and it cannot be taken on an aircraft with my 'grab & go' SE4. . It's 12v x 8A = 96 watts. The typical airline limit is 100 watts.

That leads me to an important consideration. The amp-hours rating of batteries can be misleading. Even with a quality brand like Tracer what matters most is its watt hours capacity and hence the watts consumed per hour (watt hours) by the device. Many battery manufacturers don't state their watt hours. But the power demands of a telescope depend on what it is doing. Think of it just like a car using more fuel when accelerating uphill. Heavy repeated slewing will deplete a battery faster than tracking.

My Evolution mount demands only 9.6v but seeks almost 2 amps when slewing.  Don't panic if you support an Evolution with a 12v battery or AC/DC supply as it will be fine and within tolerance if the amps are sufficient.  But other mounts might demand perhaps 12 volts and 1 amp. The 12v rating of a battery also tends to be notional. For example, a fully charged 7Ah Tracer outputs 13.2 volts. When down to 20% capacity it outputs 12.9v. Only when below 20% does it level out at 12v and eventually fall to 10V (before which most scopes will cut out). These are the manufacturers claimed ratings. 

A 7aH Tracer offers 84 watt-hours. On the manufacturers website it shows its typical discharge curve. If the device requires 50 watts the runtime will be as low as 1 hour 40 minutes.  If the device requires 12 watts when tracking (say 12v x 1A = 12W) it will run for 84/12 = 7 hours. However, when slewing the demand might be 12v x 2A = 24 watts, hence 84/24 = 3.7 hours.  

My recommendation would be to get TWO x 8Ah given that ONE (only) is under aircraft limit and two will suffice for an all nighter at a local dark sky site. If your scope was a Nexstar SE it would run on its AA batteries during changeover. But at home, I need a 24Ah as it runs my camera (20 watts), focuser (10 watts) and Intel NUC (peak 50 watts), hence up to 80 watts per hour (average about 60 watts), and my mount uses its own internal power supply. Power needs to be carefully calculated, especially if required to support more than a mere mount. 

 

 

 

If run 2 batteries, connect in parallel, will still be output of 13.5V fully charged, and double the ampage

Connect device with negative terminal one battery to positive terminal of second battery, across the batteries

Not sure how to connect 2 batteries in parallel

Make up a couple of small leads, one red, other black, and solder small alligator clip each end

Having batteries, side by side, connect both negative terminals together, and both positive terminals together using your made up jumper leads

 Do not connect both batteries end on, positive to negative, negative to positive, as this will give you 24volts, at existing ampage

Check battery voltage with multimeter to ensure have 12volts prior connecting your equipment

Running parallel will also give enough power for camera or guide scope

John

 

[Luna-tic]

7 hours ago, djpaul said:

Mmm might go for the 8ah. .

That's 10 hours ?

Generally, plan on about 80% usable capacity, max. Once you get to that point, the voltage starts dropping, and the mount will shut down from insufficient voltage. Also, with lithium batteries, the nominal voltage is less than a lead-acid battery, right at 12VDC, so any heavy draw will drop the voltage more quickly to an unsuitable level. If your mount draws 0.75 amps@12VDC, count on about 1.5 amps to account for slewing, temperature, reserve, etc., and select your battery capacity accordingly. Celestron's Power Tank Lithium is 17 amp-hours and will run my AVX about 4-1/2 - 5 hours on an observational night of moderate temps (battery capacity drops in cold weather).

1 hour ago, noah4x4 said:

That leads me to an important consideration. The amp-hours rating of batteries can be misleading. Even with a quality brand like Tracer what matters most is its watt hours capacity and hence the watts consumed per hour (watt hours) by the device. Many battery manufacturers don't state their watt hours. But the power demands of a telescope depend on what it is doing. Think of it just like a car using more fuel when accelerating uphill. Heavy repeated slewing will deplete a battery faster than tracking.

Most large batteries are rated by amp-hour capacity. It's all just a matter of math, volts X amps = watts; not hard to convert watt/hr to amp/hr and back, but if you assume 12VDC, as all our battery powered gear uses 12VDC, amp/hr is easier to figure duration by. The higher the amp/hr capacity, the higher the current drain necessary to drop the voltage under load, and the reverse is also true. A marginal capacity (for the need) battery will drop its voltage faster under a heavy load relative to the overall capacity of the battery. The current-draw rating of the mount spoken of by the OP is probably what it uses during tracking, and you can count on that tripling or more under high speed slewing. I just tested my EQ6R-Pro last night, as I have just built a field power system and was seeing what it was capable of. I have a battery minder that reads out volts, current and watts.  My Skywatcher (with an Edge HD 8 mounted) tracks at 0.5-0.6 amps; under a go-to slew at max speed, it draws 3.5-3.7 amps, and curiously enough, as it slows to its "centering speed", it draws 4.1-4.2 amps momentarily before dropping back to 0.6 amps tracking. A night of observing will take more power than a night of imaging just to run the mount, and current use is cumulative.

I had enough equipment connected to the system to draw around 10 amps; the voltage only dropped by 0.13 under the test load, from its nominal no-load of 12.9 VDC. That is with a 96 amp-hour deep cycle battery