Battery test (cont)

Yesterday I was able to test for about 40 minutes…

This is voltage after about 50% drawdown.
This is voltage after about 50% drawdown.

I gradually increased the power to 4500 watts and at all times the pack voltage and individual cell voltages stayed high. No sagging under load. So the problem was indeed a poor interconnection.

At 4500 watts though I got a ‘thermometer’ icon on the Torqeedo and it automatically reduced power to 4000 watts. I manually reduced it back to 2500 watts shortly after. And soon the temperature warning disappeared.

I felt the control head of the motor and it seemed barely warm. Looks like I’ll have to resort to the manual to check why. (later: this icon indicates the motor is overheating. Makes sense – it is rated as a 4kw motor and 4500 watts is 12% overpowering it)

Today I’m running the motor some more and at this moment the drawdown is 101 ah so the pack is about 50% discharged. The voltage is still good at 51v with a load of 1500 watts. Being on the dock, with the tide going out I’m running in reverse – in sync with the tidal flow. But its beginning to cavitate at this power so I’m not giving it more than this.

All the terminals, connections and cables are cold – so there’s no high resistance ‘weak links’ this time.

details in battery log

Battery test

Before venturing out into the bay I want to know the actual capacity of the battery bank. Last test showed that the capacity after a couple of drawdowns had increased to about its nominal value of 200ah. But I want to be sure and to balance the pack

By monitoring the power consumption from the pack using a Link 10 battery monitor I can know its capacity. This called for a spin up the river to use some power.

To begin with we motored at 4000 watts just for a few minutes and then settled back to about 1200 to 1300 watts which gives a speed 4 to 5 knots – aided by light wind and tide.

After half hour there is an unexpected low voltage warning. Only about 18 amp hours have been used so this is not a good sign.

I shut off the power to the motor and check the cell modules – one of them is lights off, which indicate low voltage. This is the same cell that reached peak voltage first when charging – this cell should be the most charged so its low voltage state is perplexing. The multimeter across this cell show low voltage but rising fast – already at 3 volts. The adjacent cell is stable at 3.3 volts.

Motoring at low power is ok  – around 500 watts – and at this level the cell voltage stabilises around 3 volts.  With the motor off, or at very low watts the voltage rises to 3.2.  We return to the dock using the motor at low power with occasional skirmishes at 800 watts when the wind rises to around 10 or 12 knots.

Back at the dock with the charger on,  the voltage of the suspect cell’s voltage has risen to 3.4 v and all others are around 3.3 v.

Perhaps this cell is faulty and now has a very reduced capacity? I call EVPower and Rod suggests that I clean all the terminals and connectors to be sure its not a high resistance connection thats causing the erratic behaviour of this cell.  I had sprayed Inox on all the connections and then after tightening the bolts had sprayed some battery terminal spray on them. Both of which are insulators and this may not be helping.

LFP batteries in the 'larder'
LFP batteries in the ‘larder’

Pity. I now have to clean it all off!  I have found some ‘conductive silver’ varnish which is used to repair circuit boards and the heating strips on car windows. I figure silver remain clean and conductive and will form a protective layer over the copper strips and prevent oxidation.  The picture to the left shows the batteries with terminals to the right already ‘silvered’ and those on the left unbolted ready to be put together.

To the right is a close-up of the new and the old. The yellow stuff is the terminal protector spray – which on the top hand bolt has been removed and the surface cleaned and silvered.

close up of new and old
close up of new and old

I should have them back together soon and be able to load test the dodgy cell.

I’ll place this cell at the end of the series and also below the hatch so that its easy to remove if it turns out to be dodgy.  As well, if it is, I can just bypass it and use 15 cells – that will still give 50 volts.

Back where she belongs

Current Sunshine is back in the water again after a few months rejuvenation in the boatyard.

with newly repaired bowI love the stillness and early morning light on the river. Being on the river brings a lovely energy which was missing when she was on the blocks. The dusty gritty hardness is gone now and I’m more inclined to write about her and adventures again.

I gave her just a short run when she was launched two days ago but it was enough to feel how much better she steers now that the motor turns with the rudder. Her direction when manouvring is much more precise, and especially when going astern.

And as before, onlookers were surprised at how much power the Torqeedo puts out. She quickly got to 6.5 knots and the energy that was used up has already been replaced by yesterday’s sunshine.

And talking about Torqeedo’s…  I like them so much I bought another one!  A smaller one that I can use on the Avon inflatable dinghy – and as well it is a backup for the main motor.  I also want to make a bracket to attach it to one of the floats so it can help with close quarters manouvring.

Yesterday we tested it on the dinghy using an outboard bracket that Claude has lent me – he had in his shed a bracket made especially for the Avon – he had kept it thinking it would be useful one day. Thanks Claude. It fits perfectly and we went downriver a couple of miles to test it.  It is a powerful little motor and actually has too much force for the inflatable – it bends the back of the dinghy when on full power.  Or it could mean the dinghy is not inflated hard enough!

Anyway, that’s a good start to my blogging again. More later.