Starter motor current (Bukh DV36)?

[Psycloud]

I'm continuing to sort out the wiring in my engine bay and have successfully rewired the VSR to charge leisure first rather than starter, removed a pile of cables that had been left behind by previous owners adding/removing bits organically, added fuses where there were none, and isolators where I would like them - hoorah!

 

The last thing I would like to do is add an isolator switch to the starter battery and am wondering what rating this needs to be.  According to the Bukh manual the starter is: Gear Driven 1KW output.  So, would that roughly translate to 1000/12 = 83amps, and is that continuous or is the cold crank current likely to be say double/treble to get it moving?  The switch I was going to use is rated: Rated at 300A continuous (1 hour) at 48V DC and 1000A for 5 seconds.

 

Thank you

 

[Robbo]

My 4.5litre John Deere Engine takes over 400amp (12v) to start, this is the max my clamp meter goes to.   It probably drops after a initial surge, but the engine has started so I don't know.

 

The switch will be fine unless your engine is really large and hard to start.  Use a quality one like from the likes of BlueSea not a cheap one that's the main thing for reliability. 

Edited July 27, 2018 by Robbo

[dmr]

3 minutes ago, Robbo said:

My 4.5litre John Deere Engine takes over 400amp (12v) to start, this is the max my clamp meter goes to.   It probably drops after a initial surge, but the engine has started so I don't know.

 

The switch will be fine unless your engine is really large, just use a quality one like from the likes of BlueSea not a cheap one.

Big things these John Deeres, I assume yours is the 4045?  My Beta JD3 (John Deere 3029) takes just over 350amps on a cold day, with an initial surge of over 1000amps. For years it ran via one of the very cheapo "red plastic key" isolators with no problems. I have a better isolator on there now but still not rated at 1000 amps.

 

..............Dave

[Robbo]

5 minutes ago, dmr said:

Big things these John Deeres, I assume yours is the 4045?  My Beta JD3 (John Deere 3029) takes just over 350amps on a cold day, with an initial surge of over 1000amps. For years it ran via one of the very cheapo "red plastic key" isolators with no problems. I have a better isolator on there now but still not rated at 1000 amps.

 

..............Dave

Yep it's the 4045, a nice colour of yellow as well.  Mine was initially wired by one of those cheap "red plastic key" isolators, it's now via a BlueSea e-series switch which I would recommend.

 

https://www.bluesea.com/products/category/11/41/Manual_Battery_Switches/e-Series

Specifications

Cranking Rating: 10 sec. 2,000 Amperes

DC Cranking Rating: 1 min. 1,000 Amperes

DC Intermittent Rating: 5 min. (UL 1107) 600 Amperes

DC Continuous Rating: (UL 1107) 350 Amperes DC

Edited July 27, 2018 by Robbo

[dmr]

1 minute ago, Robbo said:

Yep it's the 4045, a nice colour of yellow as well.  Mine was initially wired by one of those cheap "red plastic key" isolators, it's now via a BlueSea e-series switch which I would recommend.

 

https://www.bluesea.com/products/category/11/41/Manual_Battery_Switches/e-Series

Specifications

Cranking Rating: 10 sec. 2,000 Amperes

DC Cranking Rating: 1 min. 1,000 Amperes

DC Intermittent Rating: 5 min. (UL 1107) 600 Amperes

DC Continuous Rating: (UL 1107) 350 Amperes DC

2000 amps for 10 seconds is good stuff. We really just don't have the space for the blue sea switches as they are big. I got the best smaller ones that I could find on eBay but don't know if the spec. is honest. I carry a couple of spares.

 

................Dave

[Tony Brooks]

Apart from the 48 volts I am sure your switch will be more than adequate but do not trust that starter rating. As you correctly identify the current will be very much higher at the start of cranking or on a very cold engine. Also you can get horribly high currents with flat or flatish start batteries - although that seems counter intuitive.

 

I've been using these for both engine and domestic batteries for years on my DV36  https://www.autoelectricsupplies.co.uk/product/152.

[dmr]

This looks like the one that I used:

 

https://www.ebay.co.uk/itm/Heavy-Duty-Battery-Isolator-Switch-Cut-Off-Disconnect-Power-Kill-300A-12V/152978792981?epid=13017866728&hash=item239e3f2215:g:ZacAAOSwfuBazSEU

 

I chose these because they are an easy replacement for the old cheap "redkey" units. They are rated at 1000amps for 10 seconds which is more than enough (if its true).

 

They needed to fit on the side of the battery box and space is very tight.

 

...............Dave

 

[Boater Sam]

I use 12V/24V Lucas Style SSB106 Battery Isolator Cut Off Power Kill Switch Fixed Key, been fine for 20+ years. And cheaper than most.

 

    

[Tom and Bex]

2 hours ago, dmr said:

This looks like the one that I used:

 

https://www.ebay.co.uk/itm/Heavy-Duty-Battery-Isolator-Switch-Cut-Off-Disconnect-Power-Kill-300A-12V/152978792981?epid=13017866728&hash=item239e3f2215:g:ZacAAOSwfuBazSEU

 

I chose these because they are an easy replacement for the old cheap "redkey" units. They are rated at 1000amps for 10 seconds which is more than enough (if its true).

 

They needed to fit on the side of the battery box and space is very tight.

 

...............Dave

 

I fitted one of those for the same reasons, but melted it within a couple of hours intensive inverter use (1600w) prepping boat for painting. Fitted a blue sea one and had no problems at all with similar usage since, even though it's got a lower rating!

 

Managed to just fit it in the same location - it's not as big as it looks, only just over 2 inches square. This is the one I used: https://www.cclcomponents.com/blue-sea-system-m-series-mini-on-off-battery-switch-with-knob-red

[dmr]

Our battery box is right up against the engine so we are very tight for space. We do very little high power stuff, I run the engine/TravelPower for any big power tools, so the isolators never see and long term high current use, about 70 amps battery charging is the maximum.  I suspect all these things are made in China, probably with various factories copying and under-cutting each other, so the quality is probably luck of the draw.

 

In light of your trouble I will measure the voltage drop across ours next time I am messing in the battery box.

 

.............Dave

[Tom and Bex]

I think you're probably right regarding quality being luck of the draw. I was quite surprised it's failed so quickly though considering the rating. Must admit it was a bit of a shock when the inverter cut out and I was met with clouds of smoke coming from the engine bay!

[mrsmelly]

These are my BEP stuff I also have blue sea for changeover stuff. They never so much as get warm and take the covers off and they all look like new. Highly recommended.

[Tony Brooks]

6 hours ago, Tom and Bex said:

I fitted one of those for the same reasons, but melted it within a couple of hours intensive inverter use (1600w) prepping boat for painting. Fitted a blue sea one and had no problems at all with similar usage since, even though it's got a lower rating!

 

Managed to just fit it in the same location - it's not as big as it looks, only just over 2 inches square. This is the one I used: https://www.cclcomponents.com/blue-sea-system-m-series-mini-on-off-battery-switch-with-knob-red

 

I think the problem is the extensive use of thermoplastic so when the contacts start to warm up the plastic body softens and id pushed away by contact pressure. Then the clamping force is less so you get even more heating.

 

The more metal in the body and fixed contact mounting the better. The originals of the switch I linked to had a ceramic fixed contact mount but I suspect the modern ones are plastic.

 

I am sure Dr Bob can give more info but I suspect the plastic used for the critical parts by the likes of Blue Sea are highly modified engineering thermo-plastic or they may not use ordinary thermo-plastic at all so no softening and moving.