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djpaul

Tracer battery to power mount

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As I said, 12v is only a notional voltage. My "12v" Evolution mount will happily run on 9.6v. However my "12v to 19v" Intel NUC computer will choke on 11.4v.

Amp hours do offer a crude indication of battery power duration, but is not as accurate as watt-hours, and some manufacturers are deliberately misleading. A MaxOak K2 "50,000 mHA" assumes that rating against a single one of its 3.5v cells. At its 12v output it is nearer 17Ah (17,000 mAh). However, it's capacity is a mammoth 185 Wh. Sounds great until you learn it is limited to a mere 2.5A at 12v.  By contrast an 8Ah Tracer will support up to 10Amps, that is why it is double the price. Hence this subject may need far more thought than mere reference to Amp Hours when considering more demanding rigs, notably where Astrophotography is employed and multiple devices to be powered. 

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Adding to Noah4x4 comments.

Tracer packs are UN38 certified for air transport. This is a rigorous test.
You have no worries along the lines of the exploding hoverboards and other lithium powered device failures.

The Intel NUC has a huge inrush current. A year or so back I was looking at powering them from a different battery source.
Inrush current and duration are not specified. You need a battery (protection circuit/wiring) with high current for short duration.

Hope this helps, David.

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There are some 12v lithium batteries around that are far cheaper than the Tracers, See here: https://www.ebay.co.uk/sch/Rechargeable-Batteries/48619/i.html?_from=R40&_nkw=lipo+battery+12v

The range of output of these things (12.6 - 10.8v) seems on the low side.  (Presumably represents the output of 3 cells in series.) Asides from that, has anyone any informed comment on whether these batteries costing around £20 are any good for powering a GoTo?

As a piece of context, when I needed a replacement laptop battery I found that if I didn't pay the silly price asked by Dell for a new genuine one, the 3rd party offerings cost between £12 and £25 or so. The cheap one I bought is still working... 

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I would be very wary of the chinese ebay batteries.
Phrases like barge pole and million years come to mind.

I have seen too many pieces of equipment with incorrectly or dangerously applied lithium batteries to even consider the direct from China ebay low cost stuff.

On the big side was a Segway rider copy with around 750WH of lithium. On arrival in the UK around 1/3 of the cells were faulty and the charger was incorrectly configured.
Oh and it did not have UN38 approval for air transport, but the chinese did not let a bit of paper worry them.
They sent another battery pack by air freight again!

On the small side, my wife recently boought some heated gloves, again chinese via Amazon.
No fuse or other protection in the battery packs. This means damaged glove wiring can cause a fire in the flammable glove material.
A charger that overcharged (and would therefore damage) the battery.
No arrangement for charge balance on series cells, risking damage again.
A dangerously unsafe and illegal UK mains adapter.
This is in the process of being refunded. Amazon are asking that she find a carrier who will handle lithium batteries! They and Hermes don't want to know about handling the return.

I suppose if the power pack is in your garden, kept away from your expensive scope kit, and you charge it outdoors, don't take it into the house, and don't carry it in your car, it should be safe enough.

Oh yes. You should also consider another powerpack for when this one does not meet published specification and shuts down early.

Sorry to pour water on what might be bargain. But I have seen far too much unsafe electrical stuff from China. The items above are the tip of the iceberg.

David.

Edited by Carbon Brush
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17 minutes ago, Carbon Brush said:

Sorry to pour water on what might be bargain. But I have seen far too much unsafe electrical stuff from China. The items above are the tip of the iceberg.

A few vid's on Y'Tube of folk taking them apart to demonstrate their, sometimes potentially lethal, faults.

Dave

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It's not just Chinese batteries that can be potentially dangerous. Three years ago I unplugged a Celestron AC/DC adapter and the UK 'plug' bit that slides onto its body split into two revealing inch long still connected 220 volt/10 Amp prongs and no earth.  In any European manufactured similar device these would fix inwards (not outwards) and be enclosed in an earthed solid moulded plug. Here, the two parts of the plug attachment were just clipped together, not even reinforced by adhesive. Celestron replaced under warranty with a more satisfactory unit. 

Most people also don't realise Lithium batteries have a temperature operating range. For example,  the Tracer 8Ah states a discharging range from -10° C to 60° C, generally fine unless you are inside the Arctic. However, the charging range is merely 0° C to 45° C. So hands up if you ever leave your batteries on charge in a below freezing garage? Most battery manufacturers don't offer reliable guidance. 

If you visit a petrol station, note the "mobile phones prohibited" signage. We have all heard of exploding electronic cigarettes and hover-boards.  My advice is don't mess with cheap batteries. One nearly cost my son his life when one exploded in close proximity to gas welding bottles (not his fault). Buy only quality branded models. 

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Replies noted. I see that the cheap batteries have lithium-ion 3.7v cells, and the Tracer batteries have different technology and characteristics - for instance a LiFePo cell has a terminal voltage of about 3 volts and a lithium polymer about 3.5v.

These devices seem cheaper in the USA, where a 12v 85 WH LiFePo battery (from various suppliers) costs in the region of $100.

My sealed lead acid 7AH battery is looking tired, so I'll probably replace it sometime with a LiFePo battery.

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For me it was the environmental choice so choose LiFePo4 yes more expensive but had better discharge curve and significantly more power cycle capacity.

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44 minutes ago, noah4x4 said:

Most people also don't realise Lithium batteries have a temperature operating range. For example,  the Tracer 8Ah states a discharging range from -10° C to 60° C, generally fine unless you are inside the Arctic. However, the charging range is merely 0° C to 45° C. So hands up if you ever leave your batteries on charge in a below freezing garage? Most battery manufacturers don't offer reliable guidance.

Yes very true.

Most reputable lithium cells (or batteries) include a thermistor which connects to the charge circuit.

If the battery is too hot, or too cold, charging is not allowed and no harm is done.
This is just one of the benefits of buying an integrated solution like Tracer.
The battery and the charger are in communication.

I have yet to have an electric drill lithium charger refuse on account of the cold.
I have though had charging delayed due to being too hot.

I feel a test using batteries from the freezer might be imminent.

David.

 

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