recharging Skywatcher/Celestron PowerTank

[Aramcheck]

I recently bought a Sky-Watcher / Celestron PowerTank 17Ah. When recharging it, after a while both the red 'charging'  and the green 'fully charged' LED's are illuminated... Should I leave it until the 'charging' LED goes out, or is it already fully charged when both LEDs are lit?

Many thanks in advance

Ivor

[Carbon Brush]

Hi Ivor.

I guess the (not very helpful) response would be to suggest looking at the manual.

Having said that, I took a peek online at a charger manual and it mentioned red & yellow lights!

The setup should be incapable of overcharging the battery, so there should be no harm in leaving it connected for a long time.

The exact voltage during charge will depend on the charger type. Some give pulses of 14V or a bit more to help with sulphating issues. then back off on full charge.
Other just charge to 13.8V or a little less.
There was no detail of the charge regime in the online manual I looked at.

Back to first principles here. Measure the battery voltage.
If you measure the battery voltage shortly after charging and it is 13V or higher, regard the battery as well charged.

Never leave the battery in a well discharged state for more than a few hours. It will probably die.

HTH, David.

[Jiggy 67]

I have the same power tank, i'm currently on my second one. The indicator lights on these tanks are notoriously erratic. Both my tanks lights perform differently. On my current one the green "fully charged" never illuminates but the red light goes out. When I switch on,  the "ready to use" light comes on. It's guess work I'm afraid. Having said that, I've used mine over the last two nights and only put it on charge today (until the red "charging" light went out) and it worked perfectly. I would just give it a go......if its from FLO there's no rush to return it.

[Aramcheck]

Thanks David / Jiggy 67.

After leaving the battery on charge all day, from the Synscan handset Utility menu I'm getting a voltage of 11.5v, which is the same voltage I get when using a Mains power supply, so I guess it's fully charged...

When set to "On" the "ready to use" is lit, and when set to "Charge" both the "charging" and "fully charged" are lit.

Cheers
Ivor

[Jiggy 67]

2 hours ago, Aramcheck said:

After leaving the battery on charge all day, from the Synscan handset Utility menu I'm getting a voltage of 11.5v,

i didn't even know you could check the voltage from the handset   😀

[Carbon Brush]

11.5V is nowhere near full charge.

Either you do not have effective charging, or a cell in the power pack is down, or the handset reading cannot be trusted, or you have a dodgy handset power cable.

I would be tempted to spend on a multimeter to provide an independent check.
You are talking £20-£30, or very basic eyepiece money, for a meter that will help in all sorts of ways.

You don't have to spend hundreds on a posh meter. The low cost meters are often good to within 1% or 2%.
If really bothered, you could check it against a known good device at around 12V.

At work in everyday measurements we use a combination of cheap and decent meters. The cheap ones are considered fine for everyday use within 5%.
If one accidentally gets damaged, or left at site, no worry. We sometimes give them away to customers.
If you want a more accurate measurement, then there are two options.

The first is to pick up another cheap meter that is a different manufacturer and appearance.
Compare the readings on the two meters. It is highly unlikely the different make/model meters will have identical errors.
If they are in close agreement, you trust the display.

The second is to check the cheap meter against a known good power source, or known good voltmeter.

HTH, David.

[Owmuchonomy]

I had a 17Ah 'Powertank' for my 12" GoTo Dob.  It was as useful as a chocolate fireguard.  After a couple of months it refused to last more than 30 minutes no matter what colour the lights decided to flash.  I replaced it with a much more reliable deep cycle leisure battery.

[Aramcheck]

On 04/11/2019 at 11:33, Carbon Brush said:

11.5V is nowhere near full charge.

Either you do not have effective charging, or a cell in the power pack is down, or the handset reading cannot be trusted, or you have a dodgy handset power cable.

Thanks David. I'm getting 12.18 volts on a multimeter but 11.5 from within the Synscan "Utility" menu.

Hopefully I'll find out tomorrow night if the weather forecast doesn't change and we get some clear skies. The first couple of times we've used the Power Tank, I put it on charge immediately after use, but as only the "Fully Charged" LED came on, I didn't leave it on for long because of the 'instructions' warning about not exceeding the recommended charge times ("Explosion hazard"). However on the last session I noticed at the end of the night that the Yellow "Needs Charging" came on & I'm not sure how long that had been on whilst I was imaging that night.

I probably then made a mistake not recharging it at the end of session, instead putting it on charge the next day.

Cheers
Ivor

PS: The DC adapter for charging the tank is reading 14.8 v, so I know that is ok.

[Carbon Brush]

Hi Ivor.

Today there are cats and dogs falling from the sky and I am considering blocking each end of dob tubes to make floats.

It is therefore a good day to test a powerbank. Leave it on charge for a long time so you are confident of full charge.

Arrange a load to discharge the battery at a known rate.

For example a car sidelight (filament) bulb is often 5W or 6W. Or about 0.5 amps.
Some interior lights are 5W or 10W.

Connect two sidelights to provide a 1 amp-ish load to the powerbank and measure battery voltage against time.

It should start out at about 13V. Decaying slowly to 12V, then voltage falls more rapidly to 11V at full discharge.
At this point remove the load and connect the charger.

If the battery is in decent condition, it will take around 17 hours to discharge to 11V.

If it doesn't perform like the description above, time to take it to the recycle bin.
This where voltage drops early in discharge, or reaches 11V after a few hours.

If you try a brake or indicator light (almost 2 amps) or a headlamp (around 5 amps) the voltage at start of discharge will be lower and the capacity (amp hours) lower.

14.8V is not a good voltage to leave connected permanently. If the charger 'backs off' on full charge then you can get away with it.
My preference on lead acid is for a 13.5V or thereabouts constant voltage charger.

Higher voltage pulses are used to help remove sulphate - but you shouldn't be allowing sulphate to form.
Even then, the pulses should be limited to avoid gassing the cell. This is when the water is broken down to hydrogen and oxygen.
Some cells contain a catalyst to recombine the gasses. Others just vent if there is too much gas and the battery loses capacity.

The vapour (if allowed out) is exactly the ratio of hydrogen and oxygen to make a big bang if there is a spark - like a loose croc clip connection.
I have seen exploded car batteries from just this event.

Quite honestly I only use lead acid batteries if they are given to me. If I have to buy, it is lithium or NiCd.

HTH, David.

 

 

 

[Aramcheck]

Thanks again David - a good idea about connecting a car bulb & measuring the voltage over time & I'll test the discharge rate as soon as I get the chance.

I only got the Power Tank as it was the one recommended for the mount by FLO, so didn't really research it beforehand. The 14.8v  is from the mains charger which came with it, and according to the instructions it's best charged at between 14.5 and 15.5 volts.

It does also say that if the unit is used for too long after the yellow warning light comes on, recharging could take up to 20 hours....

It'll be interesting to see whether the 17 Ah holds up... the mount is spec'd at 3A so should in theory last about 5 hours 40mins.

Cheers
Ivor