7ah 12v lead acid battery help!

[Ben Smith]

So I have a nexstar 5se and have been looking into power sources for when I go to my dark site.

I opted for a sealed lead acid 12v 7ah battery as this is what is inside the skywatcher power tank. I got a celestron dc cable an wired spade connectors to plug straight into the battery.

I plugged it into the mount and it worked but then during moving the scope it lost power now and again. I'm not sure if I'm doing anything wrong or my mate gave me a naff battery. I've ordered a 500mah charger to see if it needs charging and I've also ordered a volt meter to test the battery.

As you can tell I'm quite new to electric powered scopes as I've had dobs in the past.

If you require any more info or pics I will happily send them

[Bizibilder]

That sounds like a dodgy contact somewhere?  It could also be the battery on the "lower limit" and in need of charging, but I would suspect the cabling/plugs.

[Ben Smith]

Well to join the spade connectors to the DC wire I used a wire from an old 35mm projector that already had them n snipped them off. Then I twisted them to each of the DC wires and wrapped some insulation tape round them it fits on the battery snug and the socket is 5.5 2.1 + as recommended by celestron

[nigelbeaumont]

You might be pulling a large enough current for short periods to lower the output voltage from the battery due to its internal resistance. I found out the hard way with a 5 Ahr battery - a 5A current would pull the output voltage below 11V within 1- 2 minutes, but the voltage would then go back up to ~13V as soon as the current stopped. I have a web link somewhere which links output voltage to current for lead acid batteries - my memory is that it us best to keep the peak current to no more than 20 - 20% of the battery capacity in Ahr, ie 0.7 to 1.4 A for a 7 Ahr one

[nigelbeaumont]

Found the weblink, it's http://corrosion-doctors.org/Batteries/nominal.htm

[Sporadic Dobstronomer]

Well to join the spade connectors to the DC wire I used a wire from an old 35mm projector that already had them n snipped them off. Then I twisted them to each of the DC wires and wrapped some insulation tape round them it fits on the battery snug and the socket is 5.5 2.1 + as recommended by celestron

If you have joined wires by twisting them together, it won't work.  You need to solder them, or use proper crimps, or use some terminal block.

[Ben Smith]

Nigel. I have no idea about how to alter current or even test it aha. I have tested the voltage of the battery and fully charged it's about 12.8v.

Sporadic, I didn't realise twisting the wires would be the problem. I'll try a proper crimp n see how that goes.

I have tried again recently and it still seems to drop in power then go back to normal now n then. My goto does get abit off but I think that's because my two bright stars are close to each other vega and archisomething as they are the only viewable ones from my garden