An electrician's lot is not a happy one

Armed with a miscellany of test equipment I have been doing a periodic inspection of the wiring in a large house for insurance purposes. There are eight lighting circuits and umpteen power circuits. It is a woeful task removing light fittings consecutively only to find yet-another with no earth, or moving furniture to gain access to socket outlet to perform earth-fault-loop and polarity tests, whilst knowing that there must be many hidden junction boxes that cannot be accessed without taking the house totally apart. At least, although they are fairly old, the cables themselves seem to be in good shape. I can understand the insurance company wanting assurance that the electrics are safe and won't cause a fire, but those inaccessible junction boxes (if they exist at all) are probably the most insidious.

King James

We have prophecy in our church. Prophecy is when someone speaks out in public what they believe God has given them to say. It is usually for exhortation. Typically a thought is implanted and the way the thought is expressed is up to the person giving the prophecy.

Many folk in our church use the King James version of the Bible for its accuracy.

So what if the prophet speaks in King James English with thee's and thou's? Do I conclude that God speaks in archaic English? I trow not! I regret that when this happens I find it hard to take the person seriously. At least we are encouraged to test the prophets. Perhaps I should be less judgmental. 

Donadea

Bike ride 44 miles, max 30.5 mph, avg 12.4 mph, destination Donadea forest park via Naas, Clane and Prosperous.  In Naas I followed the Grand Canal and found the Leinster aqueduct.

Grand canal showing Naas branch and Leinster aqueduct

Water reeds in Naas branch

Near the old Odlums Mill

Crossing the Leinster Aqueduct

By the aqueduct, this water is pumped up from the Liffey to feed the canal

The Liffey, looking southwards from the aqueduct

I had my cleated bike shoes on so could not easily explore - I thought of shedding all and fording the canal to check out the pump works, but thought better of it (lots of people about, and people think this sort of activity suspicious or at least foolish). So my next picture is not my own.

The aqueduct itself pasted from here

When I finally got to Donadea I duly ate my crisps and raisin turn-over, and drank my Club orange and then turned back not finding the 'forest park' too interesting... Possibly there might be some interesting parts but I did not have time to explore.

Donadea forest park, a less interesting part

On the way back I took the bog road to Prosperous and stopped by a peat-works with an interesting railway and a pile of waggons in the distance.

Peat-works railway near Prosperous

Programmable load

Recently I was involved in the design of a range of PCM's for lithium batteries of capacity up to 200Ah. Testing such a PCM involves dumping currents of over 200A. I work on a tight budget so purchasing a programmable dummy load for this sort of current was out of the question. So I improvised. I ended up using a combination of high wattage fixed resistors for loads up to 30A or so, a home-made water cooled load for high current, and a programmable load when I needed to tweak the current.

My programmable load was one of those projects where I did not do sufficient planning and research. I imagined it would be a doddle to make. I should have heeded warning bells at this point as I have "been there, done that" rather too many times in my short life.

Here are a few pictures of the construction of my programmable load.  The basic idea was that a cheap MOSFET can dump 10A easily, so 25 of them should dump 250A.  Each MOSFET has a 0.5R resistor in the source to help equalise current sharing. All 25 bases were connected in parallel (with 100R series resistors to prevent parasitic oscillation) and driven by an op-amp which compared the voltage on a multi-turn pot with the output of a 200A current sensor IC.

Four of the five panels, each has five MOSFET's with their source resistors

The 6th panel with op-amp circuit being assembled

Here are the five MOSFET panels about to be assembled

Almost complete

Details of a MOSFET panel

A 12V 100mm fan cools the five MOSFET panels. No calculations here: just vain hope that forced air cooling is very effective. But I hadn't bargained for the gate voltage negative temperature coefficient.

If any MOSFET took more than its share of current it would dissipate more power than the others and get hotter: this temperature coefficient would then make the MOSFET conduct even more leading to thermal runaway. My solution was to add a NTC thermistor in the base circuit of each MOSFET and cemented to its body. A bit of a cludge but it sort of works.

In the event I actually rarely used the programmable load. I found that various combinations of fixed resistors generally was adequate. But it was fun building it.

Lone camp

Cleevaun lough, Co Wicklow

Having bought a lightweight sleeping bag I thought I would try an overnight lone camp. Ali deposited me at the top of the pass above Lacken at 7pm and I hiked from there to Cleevaun lough (barefoot, with Meg). The bag wasn't thick enough - I was cold in spite of wearing everything. This is what the lough looked like the morning after.

Meg considering my legs

Sleeping fitfully I awoke the last time at about 06:00 but stayed in the tent until 07:30, then did a short walk to try to warm up (unsuccessful), then had breakfast (dry granola shared with Meg) then uncamped and set out.

Partial tracklog - starts on right

I got a bit lost in the morning mist, hence the loop above.  Thing is the lough is further around Mullacleevaun than I think, so on the way back in the mist I went further than I thought and...

Out of the mist at last

Meg loves chasing deer

The small lake on Moanbane

The larger lake on Silsean

My feet

Cairn on Silsean

Descent via the moss-forest

After the forest about 6 miles of road walking. My feet were rather sore when I got back, now treated with pink ointment.

Prayers are Jove’s daughters

Christopher Robin saying his prayers

I liked Adam Clark on Psalm 88 verse 2 "Let my prayer come before thee". Judging by what they say when praying publically, most people think prayer is us coming to God with requests like Christopher Robin. Whereas in fact Clark suggests that true prayer comes from, is inspired by God and, when we speak it out, is reflected back to Him. Thus James is able to say "You ask and receive not, because you ask amiss". So here is Clark's commentary:

"One of the finest thoughts in the Iliad of Homer concerns prayer; I shall transcribe a principal part of this incomparable passage - incomparable when we consider its origin:

Prayers are Jove’s daughters; wrinkled, lame, slant-eyed,

Which, though far distant, yet with constant pace

Follow offense. Offence, robust of limb,

And treading firm the ground, outstrips them all,

And over all the earth, before them runs

Hurtful to man: they, following, heal the hurt.

Received respectfully when they approach,

They yield us aid, and listen when we pray.

But if we slight, and with obdurate heart

Resist them, to Saturnian Jove they cry.

Against, us supplicating, that offense

May cleave to us for vengeance of the wrong.

Thou, therefore, O Achilles! honor yield

To Jove‘s own daughters, vanquished as the brave

Have ofttimes been, by honor paid to thee.

"On this allegory the translator William Cowper makes the following remarks: “Wrinkled, because the countenance of a man, driven to prayer by a consciousness of guilt, is sorrowful and dejected. Lame, because it is a remedy to which men recur late, and with reluctance. Slant-eyed, either because in that state of humiliation they fear to lift up their eyes to heaven, or are employed in taking a retrospect of their past misconduct. The whole allegory, considering when and where it was composed, forms a very striking passage.” Prayer to God for mercy must have the qualifications marked above.

"Prayer comes from God. He desires to save us: this desire is impressed on our hearts by his Spirit, and reflected back to himself. Thus says the allegory, “Prayers are the daughters of Jupiter.” But they are lame, as reflected light is much less intense and vivid than light direct. The desire of the heart is afraid to go into the presence of God, because the man knows, feels, that he has sinned against goodness and mercy. They are wrinkled - dried up and withered, with incessant longing: even the tears that refresh the soul are dried up and exhausted. They are slant-eyed; look aside through shame and confusion; dare not look God in the face. But transgression is strong, bold, impudent, and destructive: it treads with a firm step over the earth, bringing down curses on mankind. Prayer and repentance follow, but generally at a distance. The heart, being hardened by the deceitfulness of sin does not speedily relent. They, however, follow: and when, with humility and contrition, they approach the throne of grace, they are respectfully received. God acknowledges them as his offspring, and heals the wounds made by transgression. If the heart remain obdurate, and the man will not humble himself before his God, then his transgression cleaves to him, and the heartless, lifeless prayers which he may offer in that state, presuming on God‘s mercy, will turn against him; and to such a one the sacrificial death and mediation of Christ are in vain. And this will be the case especially with the person who, having received an offense from another, refuses to forgive."

Why I do not often post...

To be interesting enough to attract visitors I suppose a blog needs frequent maintenance. I feel like I am cheating, by not posting more often, those few that do read my blog. The thing is, so much of what I do would, I fear, bore my readers. Not that I am a chartered accountant mind you. Much of the time it is "all work and no play" but actually I think some of the work things I do are quite exciting. But I am not at all sure that you would agree. Like figuring how to integrate a direct feed hot water supply from a Turboburn boiler with an existing conventional hot-water-cylinder system, or how to design a USB-dongle to provide GSM communications.  I could talk about those sort of things if people were interested...