So I started the engine with the EHU plugged in... (1 Viewer)

[RogerThat]

Turns out that wasn't such a good idea

For some reason, probably haste, I started the engine while the EHU was plugged in and the control panel switch set to cab battery (as I was topping up the cab battery as it's been laid up for a few weeks).

Didn't realise at the time but I've blown the little glass fuse in the charger(?) as I now have no 12v power when switched to 'cab' but normal 12v when switched to 'hab' battery (I have 12v ok when on EHU still).

Looking for these funny little glass fuses (250v 15A 5mm X 20mm), I have found somewhere that sells them (eBay) but I don't know if I should be buying slow blow fuses or fast blow fuses?

I assume fast, as you'd want it to pop quickly, before something more serious got damaged?

 

[haganap]

take it to Maplins. Sorted me with a fuse for my heater this weekend.

 

[Stealaway]

I'm 99.9% certain it will be a regular fuse. Slow blow are rare and rarely used.

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[Lenny HB]

Slow blow/Anti surge fuses have a 'T' before the fuse size i. e. 5 would be T5A.
More worring is why should starting the engine withe mains plugged in cause any damage, never heard of that happening before.

 

[RogerThat]

Seems a fast-blow fuse is winning then!

@Lenny HB thanks for the 'T' heads up, good to know.

In terms of it damaging something, it even states in the manual that I shouldn't have done it:

Broken Link Removed

I guess it's down to the age of the vehicle / circuits? Technology has (thankfully) moved on since my motorhome was made

 

[pappajohn]

Not surprised it blew....

You had your charger connected to the engine battery.....the starter began turning trying to draw 200a to 400a.
The battery can supply that but the starter will get its power from wherever it can and the charger is in effect an electronic battery.
In the same way if you have two engine batteries the starter draws from both, not just one.

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[tonyidle]

That's saying that if you have the mains charger switched to charge the cab battery the fuse will blow if mains is connected. Sounds reasonable.

 

[Gromett]

Not surprised it blew....

You had your charger connected to the engine battery.....the starter began turning trying to draw 200a to 400a.
The battery can supply that but the starter will get its power from wherever it can and the charger is in effect an electronic battery.
In the same way if you have two engine batteries the starter draws from both, not just one.

I can't see it being that. The charger sets the output voltage to get the desired current. So if a larger current was requested the charger would lower the voltage to one far enough below the battery voltage to not have an over current situation.

My guess would be that is was caused by a spike when the alternator turned. Any inductive load when switched off will spike a high voltage in the reverse direction to the original voltage polarity. This is usually prevented by installing a flyback or snubber diode. My guess is that there is no snubber diode. The charger probably has a relay that connects the charger to the cab battery when 240v is supplied. So when you pull the power lead out of the EHU socket this relay disengages and disconnects the charger from the cab battery to prevent this spike. Hopefully the fuse has protected the output mosfet on the charger. My guess would be a high speed fuse was used.

I only know this because of the Arduino fridge project. I have had to design in a snubber diode to prevent the flyback spike from the computer fans damaging the PWM mosfet..

 

[Gromett]

Thinking about it a bit more, The fuse could also be part of a reverse polarity protection circuit and the charger may have a diode to cause the fuse to blow when reverse polarity is applied. This may be triggered by the induced (reversed) voltage from the alternator. This is the reason your ciggy lighter sockets go dead when you are starting the van I would guess to protect sensitive devices from this spike.

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[Popeye]

I'm sorry for your trouble but grateful for this thread, I admit to regularly starting the engine whilst the mains is till attached, please tell me if I'm likely to harm something in some way... Griff

 

[jonandshell]

Of course, you have to also consider the effect of AC being connected to the DC starter motor on startup.
When you turn the key, the engine will be turned in both directions at 50 times a second.
If the engine happens to be turning backwards when it fires, you could end up with on one foward gear and six reverse ones.
This typically happens in French and Italian motorhomes. As well as their military vehicles.
World War 2 would have had a different outcome if they had understood reverse polarity and had the appropriate EHU leads!



Please take the above advice with a pinch of salt!

 

[tonyidle]

I can't see it being that. The charger sets the output voltage to get the desired current. So if a larger current was requested the charger would lower the voltage to one far enough below the battery voltage to not have an over current situation.

My guess would be that is was caused by a spike when the alternator turned. Any inductive load when switched off will spike a high voltage in the reverse direction to the original voltage polarity. This is usually prevented by installing a flyback or snubber diode. My guess is that there is no snubber diode. The charger probably has a relay that connects the charger to the cab battery when 240v is supplied. So when you pull the power lead out of the EHU socket this relay disengages and disconnects the charger from the cab battery to prevent this spike. Hopefully the fuse has protected the output mosfet on the charger. My guess would be a high speed fuse was used.

I only know this because of the Arduino fridge project. I have had to design in a snubber diode to prevent the flyback spike from the computer fans damaging the PWM mosfet..

That assumes the charger has over-current protection. Not all have in my experience - unless you count the fuse .

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[Geo]

Having read the context from all the expert posts above and taken a second look at the pic of your
manual that you posted I am now convinced you shouldn't a done it
Dont do it agin
Geo

 

[Neilfg]

Quite impressed with manual and that you had read it. Amazing what info can be found in them squirreled away.

What van is it and how old is it?

 

[Neckender]

@Popeye

I'm sorry for your trouble but grateful for this thread, I admit to regularly starting the engine whilst the mains is till attached, please tell me if I'm likely to harm something in some way... Griff

Depends if you're cooking Spinach at the same time.


John.

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[Gromett]

Of course, you have to also consider the effect of AC being connected to the DC starter motor on startup.
When you turn the key, the engine will be turned in both directions at 50 times a second.

AC won't get through to the engine even with the charger on and EHU connected. The charger rectifies the AC to DC and smooths the and regulates the output...
Funny thought though

 

[Peter A Forbes]

If the charger has current limiting, it should tolerate the engine starter load being put across it, but many don't and there's your fuse gone.

Our rail chargers have to charge down to almost a short circuit, train lights left on in the sidings, battery flat....

Peter

 

[RogerThat]

Quite impressed with manual and that you had read it.

Thanks

What van is it and how old is it?

It's a Swift Sundance 590RL, approx 17 year six old

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[Gromett]

It's a Swift Sundance 590RL, approx 17 year six old

Have you got the fuse replaced yet? Is everything ok now?

 

[pappajohn]

Thanks



It's a Swift Sundance 590RL, approx 17 year six old

There you go then.
Old style analogue charger with no current limiting.

 

[RogerThat]

Have you got the fuse replaced yet? Is everything ok now?

No, not yet, I ordered a pack of 10x fuses on eBay for the princely sum of £2.95 (delivered ), but as it often the case I'm still waiting for the postie to deliver them

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[Gromett]

No, not yet, I ordered a pack of 10x fuses on eBay for the princely sum of £2.95 (delivered ), but as it often the case I'm still waiting for the postie to deliver them

ok. Keep us posted please

 

[Spanishsteve]

I only know this because of the Arduino fridge project. I have had to design in a snubber diode to prevent the flyback spike from the computer fans damaging the PWM mosfet..

This is like reading a foreign language ! Cue tumbleweed blowing past my brain.

 

[rangi]

Quite impressed with manual and that you had read it. Amazing what info can be found in them squirreled away.

What van is it and how old is it?

What??? We are supposed to read instructions??

Good grief , no ones told me that Who can I sue?

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[RogerThat]

Have you got the fuse replaced yet? Is everything ok now?

I'm pleased to say, postie delivered the fuses this morning, five minutes later and I had everything tested and all working again

 

[Gromett]

I'm pleased to say, postie delivered the fuses this morning, five minutes later and I had everything tested and all working again

Fantastic. Fuse did it's job and protected valuable equipment from user

Big relief.

 

[Bart]

Super job Roger .

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[wizzer59]

Probly got a little water in it then













Sorry couldn't resist