Jaycar Lithium Ion Laptop Power Bank

[floyd_2]

Hi guys,
just wondering if anyone here has seen the Jaycar Lithium Ion laptop power bank (link here (https://www.jaycar.com.au/6-600mah-laptop-power-bank/p/MB3719)). Whilst it isn't a power house, I was wondering if it would be a useful item to power an AZ-EQ5 or whether it simply wouldn't cut it. My observing only every goes for a few hours at a time (visual only).

[jenchris]

That would run a eq5 all evwning no problem

[Imme]

I believe the EQ5 pulls up to 2 amps when flat out (both motors slewing)

That battery seems to be 6.6 ah (amp hours)......meaning it can provide 6.6 amps over a 1 hour period before it dies.

2 amps in to 6.6 amps means you would get just over 3 hours with both motors slewing fast.......obviously this only happens for short periods and you normally only have 1 motor tracking slowly.....in other words you should get a night out of it easily.

[floyd_2]

Thanks Jennifer and Jon. Much appreciated. I was looking at Celestron offerings and thought their latest power bank, whilst being very cool battery technology, was very expensive. I have a 7.5AH 12V SLA on my desk here doing nothing too so may even use that puppy (if it still charges that is).

[AndrewJ]

I like how the fast recharge takes 7hrs but
the slow recharge only takes 6 ?????

Andrew

[floyd_2]

I saw that and started laughing - I'd be doing the slow recharge every time - just to save time lol

[Wavytone]

Max output is 3.5A, should give you a good nights running.

One thing to watch with this type of battery is the output voltage - if it is discharged below 2.5V per cell ie 10V total, you will do permanent damage to the cells reducing its capacity.

On the AZEQ6 - which can pull close to 4A these powerbank devices can’t supply the peak current when slewing and the result is the motors stall, which sounds like an ugly scream.

I’m using a 12AH SLA...cheap, works fine.

[AndrewJ]

Gday Wavytone
Looking at the battery, it says it has a 5V charge voltage ( ie they say you can charge it from the equivalent of a USB port ) and can put out 12,15 or 19V.
Im wondering if this beast only has 3.3V cells and uses a DC-DC converter to get the reqd output, in which case, by the time you see a drop in output voltage, its too late.
The manual and data sheets are a joke, so cant tell more than that at present.

Andrew

[glend]

Beware the voltage drop under load. Slewing, say to a target from home position, where both axis motors are running, is the big test for these small batteries. You really need a VU meter to see what happens under load, don't let it drop below 12V. It might say 12.6v at rest but the full load output is the important number. Better too much capacity than too little.

[floyd_2]

To get a bit of closure on this topic I purchased one of the Jaycar batteries to try it out. I can confirm that they're not up to the task. The draw from the mount is just too much for them. The mount doesn't complain about low power, however, the battery only lasts about an hour with tracking only (no slews). I returned it this morning for a full refund. Was interesting to try anyway.

[Steffen]

Yes, it most likely has 18650-style cells, with a cell voltage of 3.7V. That in itself is not a problem, the DC-DC inverters often have around 90% efficiency these days. However, the capacity (6600mAh in this case) is usually given at cell voltage. This means, the pack can store 24.4Wh, or a mere 2Ah at 12V.

Some of the more reputable battery pack makers quote the capacity in Wh, to remove this uncertainty. With all those that didn't that I ever encountered, the Ah figure was at cell voltage.

[AndrewJ]

Gday Steffen

Understood.
I actually built my own step up converter into the base of my ETX many years ago, ( when components were big enough to be soldered with an oxy torch :lol: ) so i could run it off anything and have a constant voltage to keep the encoder calibration OK.
Problem is it is so good at holding the output voltage, it can suck the battery to dangerously low levels before you notice it :-)

Andrew

[Steffen]

Yes, it'll suddenly drop dead. You'd definitely need one of those inline battery watt meters to know where you stand.

[AndrewJ]

Gday Steffen

They dont help much unless they show voltage, as the power drawn is pretty much the same, just as the battery voltage drops, the current goes up to compensate ( till it glows and the low ESR capacitors pop :-) )
I ended up getting a simple low voltage battery cutoff unit i can stick on the battery itself. It just cuts out at a set point, so no need to watch

Andrew

[Steffen]

They show everything. Voltage and current draw as well as peak current, minimum voltage, watt-hours and ampere-hours since power-up.

http://www.ebay.com.au/itm/Digital-LCD-Watt-Meter-Battery-Balance-Ammeter-Amp-Analyzer-60V-100A-DC-RC-Volt-/221399347636?epid=1194978212&hash=item338c6df1b4:g:niAAAOxykmZTL Y4G

[AndrewJ]

Gday Steffen

I cant seem to find a manual for them.
Do you know if they have a low battery cutoff function, or is it something you would still need to watch????

Andrew

[Steffen]

You'd need to watch it yourself, it has no active functionality, just display.

For example, I know my current AGM battery has 40Ah capacity, so I watch that I never draw more than about 20Ah out of it before recharging. I also check out the peak amps of my observing sessions, to see whether the mount or any accessories are misbehaving.