Had to reinforce my off-grid wiring.

[DamonHD]

Under heavy load (in this case, my server/laptop battery recharging) my off-grid system LVD and the laptop power converter would oscillate madly (~2Hz) and eventually the laptop would turn itself off completely, presumably protecting itself from dirty power.

I had already doubled up the -ve wiring from the battery and done some other tweaks, which seemed to help, but after several shutdowns yesterday I doubled up the +ve side as well and so far things are looking better (I could not reproduce the problem).  Time will tell.

Unfortunately this makes my wiring messier and more complex than I would like, so I've started labelling it, since I've had to break some of the colour/usage conventions.

Time to print and stick up a schematic.

Rgds

Damon

[SparWeb]

You're getting voltage drops in the inverter-to-battery wiring, aren't you?  What gauge of wire have you used, and how much current is being drawn when the computer's PSU starts acting up?

[DamonHD]

Hi

There's no (AC) inverter since it's all low voltage DC, but the yes, it's the wiring between the battery (downstairs) and the laptop's DC-to-DC converter.

That wiring segment is probably less than 5m and I have at least 1mm^2 cores, now doubled up.  (I have been using standard 13A and 6A 240V mains cabling inside.)

I even have a nice fat 68milliF cap just upstream of the LVD to try to overcome upstream inductance effects when it first switches on.

I may go and shorten some other segments upstream of the battery (ie from some of the panels) to lower system impedance even further when the sun is out...

Rgds

Damon

[TomW]

I am assuming [dangerous perhaps] you understand the need for good, clean and solid connections?

Not connecting copper to aluminum or other dissimilar metals in buss bars / cables/ connectors? At least without proper no-ox or other preparation for differing metals.

You could be amazed how a cruddy connection can suck power and cause voltage to drop when current flows.

Always better to go over sized on cabling runs.

It is also perfectly functional to gang up conductors for added power handling.

Just some thoughts.

Tom

[DamonHD]

Hi,

Yes, I understand the badness of poor/oxidised connections (and have fixed many a complex gadget with an "engineer's thump" over the years).

I don't think I have any dissimilar metals inside in the relevant segment (all copper based wiring, connector blocks, etc, or tinned), though there is some Al wiring from one of the panels outside.  I will check for corrosion there since you prompt me.

In general I hoped that I was oversizing everything, and I had left myself spare/unassigned wiring just in case.  Paranoia paid off again, it seems.  My new external wiring is 40A-rated at £150 for a 50m reel...  I couldn't drill holes big enough to get that through the floorboards though!

But yes, thanks for the reminders.  All good stuff.

The system has played nice again today...

Rgds

Damon

[joestue]

it's almost as if you don't have a battery, with the converter and charge controller oscillating about the solar panel's load curve.

[Flux]

Try measuring volts directly on the battery terminals and also on the dc converter terminals. I don't get the impression that you are taking a lot of current but even so 5m of cable between a battery and a voltage converter is a tall order.

You also mention a lvd and this could be adding more drop and problems if you already have significant volt drop issues.

Capacitors across the converter will only help during transient loads, fine for an inverter starting a motor perhaps but it will do little to help you with a constant charging load, spend the money on copper not capacitors. Best solution would be to move the battery near to the dc converter, the solar wiring is far less critical and could be extended.

Flux

[DamonHD]

Thanks Flux!

We're only generally talking about a max of ~6A at 12V, and more usually nearer 2A.

That 6A is when I'm effectively dumping excess with my software dump load!

It's difficult to measure the voltage at the battery and at the converter at the same time as they are on different floors, but the LVD (my home-brew design, see http://www.earth.org.uk/low-voltage-drop-out-circuit-design.html ) is inches upstream the DC-to-DC converter and it did oscillate much much worse (basically for every 'on' transition) before I added the cap, since the converter takes a huge slug of energy to start up I think.  Note also that demand from the laptop seems remarkably spiky, especially while it charges its internal battery.  I can't reasonably get the battery physically any closer to the load, and I didn't leave much slack in the wiring as is.

After my next planned 10x expansion in battery (if it comes to pass), the batteries will drift yet further from the load unless I can get the Li-chemistry ones, as there is not space to accommodate 400Ah of SLA in the house safely...

(The LVD is set up to come on somewhere over 13V and drop out a little over 12V, BTW.)

But yes, it is interesting to see in practice how valuable the extra copper is.  I shall continue to mentally oversize the wiring from now on with a "double it, and again..." approach!

Rgds

Damon

[elvin1949]

 Damon

 That is what i have always done on low volt systems.Figure the wire size needed then double it.

 I would also adjust the lvd UP about 0.5 volt on both ends.I think it is set to low,just my opinion,

ain't worth much BUT might help.

later

Elvin

[DamonHD]

Hi,

At the moment it all seems stable so I'm not fiddling with it again for now!

(The voltage is set by soldered in resistors since I don't trust trimmers not to drift or inject noise or go open circuit...)

Rgds

Damon

[Darren73]

Hi Damon,

It might be better to move the LVD to the battery end of the cable, that way it's protecting the batteries without having to worry about the varying voltage drop on the cables due to varying load, it also won't suffer from any inrush surge as the battery will be a far more stable source.

Regards

Darren

[elvin1949]

   Damon

  I agree if it ain't broke don't fix it.

Just watch your battery voltage,if it stays in spec's it's ok.You may need to add another battery

if that one is full charging.

 I Enjoy watching your progress.

later

Elvin