Power problem

[I.C.D]

G’Day All
My observatory is run on two 12 volt batteries charged by a 80 watt solar panel through a solar regulator .I have two 12 volt Dc/240 Ac volt inverters one is 300 watts the other is 150 watts. The trouble I am having is when the power supply on the laptop starts to charge the battery on the laptop no matter which inverters I use they both start to scream low voltage even through both batteries are showing 12.5 volts.
The inverts I have are not a pure sine wave inverters , could this be the problem or is the laptop drawing to much power from the batteries for the inverters to handle.

Ian .C
:shrug:

[glend]

What is the current draw of the laptop power supply? Some low powered modified sine wave inverters don't perform well with laptop power supplies. The newer pure sine wave inverters are fairly cheap now and worth a look. I would think you would be fine with one of 600 watts continuous.

How many total amp hours are your batteries? And how old are they? Are they wired in series or parallel?

[I.C.D]

G’Day Glen
I have two 6 volt 200 amp hours in series about 6 years old and one 12 volt deep cycle 100 amp hour 6 months old, both batteries are on different circuit .The lap top on charge drawing about 4 amps
Ian .C

[BPO]

Hi Ian.

Are you sure the cells are fully charged (~13.6V on charge and ~12.8V off) before and when you load them up?

A healthy 80W panel outputs ~4-5A max. in direct sun, so it'll be struggling to keep up with demand if you're using the battery bank regularly and/or for extended periods. (Or after extended cloud cover.)

And I also second the suggestion you upgrade to a pure sine wave inverter. Mod sine can play merry hell with some devices, including charger/PSUs.

[I.C.D]

G'Day ,BPO
They do charge up 13.5 v and drop to 12.5v ,the most time I would use the system would be about 4 to 5 hours a night (not every night) and nothing is running during the day .What size pure sine wave inverter would I need to run the laptop because I think the type of inverter I am using may be the problem.
Ian C

[BPO]

Hi Ian.

After a full summer's day of sunlight (especially if you're turning and tilting the panel to track the sun) those cells may charge fully, providing there's no load on them. The only way to really tell is by connecting (say) a clamp meter and checking the input (charging current). If it's in the low mA at the end of a day's charging (while the sun's still high), the cells are probably in good shape.

The voltage will be anywhere up to ~14.5V while still on charge, depending on the cells and regulator/charger, but that will drop to ~12.8V (fully charged healthy battery bank) as the surface charge dissipates after charging. If they soon drop much lower than that (below ~12.7) without a load on them you have a problem.

Most laptops will happily operate off anything rated above 150W, and you won't be placing too much additional load on a healthy battery bank running anything rated up to ~600W. Anything higher and you're wasting a bit of battery power (not a lot, though). Best to get one that will cover all present and immediately foreseeable loads.

Pure sine wave inverters are now so inexpensive you can always add another later, although right now I'd recommend you consider adding additional solar panels. They're becoming amazingly inexpensive: You'll get a 250W panel now for the same price as you'd have paid for an 80W only a few years ago.

(Higher capacity panels are almost always 24V, so you would have to reconfigure your battery bank. Not a problem, as most regulators auto-detect and switch voltage, and many MPPT regs can drop V. Plus, 24VDC-230VAC pure sine inverters are equally common, and you can use lighter cable in your system, or longer runs.)

[I.C.D]

G’Day BPO
Thank Mate for the info sorry for not getting back to you earlier been on a little bit of R&R for Australia Day .Yesterday afternoon I when through the wiring from the batteries to the distribution panel and found a couple of terminals had come loose which may have been causing all my problems .
I will be also be changing over to pure sine wave inverter to run the laptop as I have notice that the loptop was getting warm to touch .

Ian.
:thanx:

[frolinmod]

My laptop has a feature that allows me to disable battery charging while plugged into an external power source. Disabling laptop battery charging cuts the laptop power usage in half. I don't want or need the external power source to charge the laptop battery, just to power the laptop, so I always turn this feature on when I'm in the field running off a set of external lead acid batteries. If I want the laptop battery charged, I'll charge it some other time/place. Does your laptop have a "disable battery charging" feature? And of course for the smallest power draw use a DC/DC converter to power the laptop rather than an AC adapter.

[Irish stargazer]

Just a thought. I think that some invertors need to draw a certain amount of current to achieve a stable output. It could be that when your laptop battery is fully charged it is not drawing enough current to maintain the voltage. Try adding an extra small load and see if it is more stable.

[I.C.D]

G'Day mate
Sorry for not getting back to I have been in hospital having my shoulder muscle stitch back to my shoulder before they snap .I am going with a DC/DC converter to power the laptop I can get a dell car charge from the states as Dell in Australia don't carry them ,so I hope this will fix my problem
Ian C :thanx:

[acropolite]

Ian,

I bought a nice aftermarket laptop PSU at Jaycar which runs most laptops complete with multi adapters which also set up the correct voltage and polarity for the laptop. Unfortunately I can't see the one I bought in the catalog so I can't give you a link.

A bonus with that PSU is that it has a 12 V input as well as a USB charging output. That would solve your problems by allowing you to run directly from 12V.

Regarding the inverters, your problem may be the wired connection from the battery to the inverter, when running at 300W your inverter will draw around 30amps, even a fraction of an ohm resistance in the DC path will cause a voltage drop, for example at that current 1/10 of an ohm will result in a drop of 3 Volts, basically the inverter would have likely stopped. Laptop PSU's can draw up to 90W, so your current draw at 12V is still significant. If your inverter has removable leads, try measuring the voltage (under load) at both the battery and entry point to the inverter.

[I.C.D]

G'Day Phil,
I think you may have hit the nail on the head I am running 5mm cable about 1.5 m from the battery to the DB and 2.5 m from the DB about 300mm to the inverter .Do you think I should run 5mm to the inverter as well. Ian