Battery master switch failure

[Rick-n-Jo]

A little puzzle for the electrical bods here. Comments and opinions welcomed.

 

A few days ago I was moving "Pleiades" to Saul Junction in the gathering dusk (we had a timber delivery the next day, so looking for a lorry friendly mooring). As I was reversing towards a suitable mooring space, suddenly all the lights went out, and as she is diesel/electric drive and I was making the short journey on battery power only, I lost propulsion as well. Fortunately the wind had fallen to a gentle breeze so I managed to go below and restore power by switching the battery off and on a few times, before we hit anything.

 

The switch is a BEP Marine item, rated at 600 amps. Contacts are a copper/brass plate rotating over a pair of electroplated copper bolts. Not very sophisticated.

 

Later investigation showed that the contacts were badly burnt and eroded.

 

 

I initially suspected that the culprit was the propulsion motor speed controllers, as these contain several large capacitors that charge up quite abruptly when a battery is first connected, giving a big and noisy spark. However I have a contactor (big relay) fitted, with a 470 ohm 2W resistor bypassing its contacts, which is supposed to charge the capacitors slowly enough to avoid the big spark. To test if this was the cause I disconnected the motor circuit completely, leaving the rest of the boats systems as normal. Reconnecting the battery still generated the big spark. Further elimination showed this to be down to the inverter/chargers.

 

Oh ho! Suddenly, this appears to be not just a problem with my system, but potentially for any one which has similar equipment.

I have two Victron combi inverter chargers, model 48-3000-35. I'm guessing they also contain capacitors sufficient to cause significant arcing when the battery switch is turned on. I don't know if the problem is worse as these are 48 Volt items. I do know that battery switch failure is not uncommon.

 

My proposed solution is to do something similar to the motor circuit. I propose to put a 470 ohm 6W power resistor in series with a push button switch across the battery switch so that pushing the button for 20 seconds or so will bypass the battery switch and pre-charge everything before turning on the main switch.

 

Will this solve the problem? Anything I'm missing? Over to the experts!

 

Rick

[RLWP]

This is of no help to you at all, it just came to mind reading your post

 

 

Richard

[Mikeonb4c]

I've got to ask - what is a diesel electric drive? I mean, I think I should know, but I was wondering only tonight if anyone used electric motive power for their narrowboat and - if so - what was the upside and downside.

[Rick-n-Jo]

This is of no help to you at all, it just came to mind reading your post

 

 

Richard

 

I notice Pat Travers also has a song on there called "Crash and Burn", which is what my clunky old PC does these days if I try to watch YouTube.

 

PS mods (grovel grovel)

 

I did all that typing and spellin' right, then went and put it in History and Heritage

probably ought to be in "equipment" but I don't think I can move it.

 

Rick

[Rick-n-Jo]

I've got to ask - what is a diesel electric drive? I mean, I think I should know, but I was wondering only tonight if anyone used electric motive power for their narrowboat and - if so - what was the upside and downside.

 

What it sounds like really. Electric motor drives the prop. Diesel engine makes the electrickery. There are various permutations possible (Google "serial hybrid" or "parallel hybrid" for some light reading!)

Ours is a battery buffered series hybrid (I think)

 

Small DC generator drives DC motors and charges big battery. Battery provides extra power for speed or manouvering. Boat can also operate on battery power alone.

Battery plus inverters provide lots of on board mains voltage power.

 

Downside - the initial cost is higher than conventional.

Upside - only one (small 500cc) engine aboard, but as much domestic power as if we had a propulsion engine and a 6KW generator fitted. Running costs should be lower.

Oh yes, and it's ever so quiet!

 

 

Rick

Edited July 31, 2010 by Rick-n-Jo

[Radiomariner]

The "tracking" marks on the photo seem to indicate that electrical equipment (Load) is still in circuit when the switch is operated. If the two inverters are in circuit when the switch is operated arcing at the switch is inevitable. You should ensure that all such equipment switched is off before operating the isolating switch (Emercencies excepted of course), or get a higher rated switch or even consider a power contactor.

[barge sara]

We had a similar battery switch fail, just melted under load.

I was using one of these as the isolator in the generator line, switch was rated at 350 amps, but melted with only 250 amps passing through. No make/break arcing, just couldn't take the current.

I replaced it with a similar one and monitored its temperature and it too quickly heated up. Checked the voltage drop across it and realised that basically these switches are crap, have huge internal resistance and won't handle their rated current without burning out.

 

I've now replaced it with a forklift 'hit button to stop' switch, which is basically a contactor with a manual action; i.e a spring loaded breaker with big meaty contacts rather than a flimsy wiper switch.

These are designed to break under full load and have minimal internal resistance.

Problem solved.

 

I bought it from Battery Power systems, and it wasn't much more expensive than the 'Marine' badged battery switch.

Also had to buy an enclosure to mount it in.

BPS do all sorts of useful high current DC kit - good for electric boats!

 

HTH

All the best.

Edited August 1, 2010 by barge sara

[barge sara]

Glad to see electric boats now have a place in History and Heritage!

[Rick-n-Jo]

The "tracking" marks on the photo seem to indicate that electrical equipment (Load) is still in circuit when the switch is operated. If the two inverters are in circuit when the switch is operated arcing at the switch is inevitable. You should ensure that all such equipment switched is off before operating the isolating switch (Emercencies excepted of course), or get a higher rated switch or even consider a power contactor.

 

Exactly. Since I tested with all loads switched off, and still get a spark when connecting, that leads me to suspect that the inverters have conponents (capacitors?) that are always connected, even when the unit is turned off. If so, that is a problem for all users of similar equipment.

 

 

John, thanks for the link. I will certainly be looking for a replacement for that BEP switch, which looks like a very expensive load of rubbish!

 

Rick

Edited August 1, 2010 by Rick-n-Jo

[andywatson]

I've now replaced it with a forklift 'hit button to stop' switch, which is basically a contactor with a manual action; i.e a spring loaded breaker with big meaty contacts rather than a flimsy wiper switch.

These are designed to break under full load and have minimal internal resistance.

Problem solved.

 

I bought it from Battery Power systems, and it wasn't much more expensive than the 'Marine' badged battery switch.

Also had to buy an enclosure to mount it in.

BPS do all sorts of useful high current DC kit - good for electric boats!

 

HTH

All the best.

 

Good info thanks.

The switches on the BPS site look very sturdy and crucially spare internals are available.