In France - Bongo not starting

[missfixit70]

So how does that apply to a bongo Teenmal, with a 30 amp fusible link for 4 glowplugs? where did you get those figures from?

[missfixit70]

Hi

thanks for reply, yes would not put in a higher fuse if the fusible link was 30A, thanks for confirming. One of the links refers to a resistance of 0.5 ohms per plug, I was getting more like 2.0 ohms on each glowplug. Would that explain it, ie new glowplugs?

Thanks

K

I would say so
Was that with the glow plug rail removed?
Was the glowplug rail & all connections sound & tight? Higher resistance due to an iffy connection would draw more current.

[eoptio]

Hi

yes with the rail removed. All connections are ok, rail has an insulating layer on it, not touching any metal anywhere. Odd though, when we first had the Bongo the glowplugs did not work well (lumpy start etc), that did not blow the fusible link at the time, replaced the plugs at that point (1.5 yrs ago) and has been working ok since. Will have a look at new plugs, NGKY701J (it's a 1995 2.5 TD)?

thanks

K

[missfixit70]

Were they cheaper no name glowplugs? most that have replaced plugs with "cheaper" brands have had issues in a very short time. NGK's are the way to go

[eoptio]

not sure what brand they were, got them from one of the shops selling bongo parts. Is the correct NGK part number NGK Y701J?

thanks

K

[missfixit70]

Seems to be right,
http://www.igmaynard.co.uk/bongo/forum/ ... gk#p475269
(note, most of the answers found today were simply using the search function & a bit of common sense )

[g8dhe]

This article from NGK covers the 701J (Self Regulating Metal) type, the Current and temperature are shown in graph format under the "Glow Plug Types"
this shows 17 Amps peak and 5 Amps after 5 seconds hence why the fusible link rather than a normal fuse is used, its a very slow blow type of fuse so can handle the peak current and yet still blow if the current exceeds about 20 Amps for any length of time.

[eoptio]

thanks that's interesting. I think I will replace the glowplugs anyway, however before doing so I'll have a further look at the fuses: the odd thing today was that if I connected two glowplugs the 30A fuse did not blow, when connecting a third (irrespective which one) the fuse would blow. If there would be a short on the system somewhere I would expect the fuse to blow irrespective of how many plugs are connected, if the cause would be a faulty plug, I would expect the fuse to blow only when the faulty plug was connected. Instead the fuse blew when additional plugs were connected which seems to suggest a higher than 30A draw when three plugs are connected which could be explained by a high initial draw. Odd though that others seem to have been able to make it work ok with a 30A fuse?

Sofar I have used normal automotive fuses with two strands of (I think) 20A wire. I'll see if I can get some 10 or 8 AWG wire trow, a maxi fuse holder and a few 30A and 40A maxi fuses and see what happens then.

Thanks

K

[missfixit70]

This article from NGK covers the 701J (Self Regulating Metal) type, the Current and temperature are shown in graph format under the "Glow Plug Types"
this shows 17 Amps peak and 5 Amps after 5 seconds hence why the fusible link rather than a normal fuse is used, its a very slow blow type of fuse so can handle the peak current and yet still blow if the current exceeds about 20 Amps for any length of time.

Looking at the graphs, it looks like you've got 2 different lots of data mixed up there Geoff, the "SRM" type 701J plugs show 17 amps peak, dropping to 10 amps by 10 seconds with a low of @7.5 amps after 60 seconds, which puts 4 x glowplugs at 30 amps draw at their lowest Not sure how much I trust a graph that measures voltage in (A) though

[Trouble at t'Mill]

Hello Eoptio.

Glad you got home ok - what a forum, eh?!

I understand what you're saying when you explain how 2 plugs are ok and adding any third makes the 30A fuse go 'pop' as suggesting that there isn't a short anywhere on the circuit as surely even one would make it go 'pop'? However, shorts aren't always 'dead'-shorts; they could be partial - enough to tip the circuit over the edge when 3 plugs are drawing current. So, you can't rule out there being a wiring problem somewhere...

Neither am I saying - of course - that there IS a partial short there! We just don't know what the problem is, because the cause hasn't been found yet, only speculated on. And it's vital to know with absolute certainty what the cause is - electrical faults can be nasty things.

Do you have a digital multimeter of any kind, even a cheapo? If not, now's the time to get one and make it part of your tool kit! They need cost no more than a fiver, and even these will measure down to tenths of an ohm and up to 10 Amps.

The arithmetic involved here is nicely simple, and involves just Volts, Amps and Ohms. I don't know what the fuse rating is for the glow-plug line, but most on here suggest it's 30A. When the glow plug element is cold, it's resistance is much lower, so when the ignition key is first turned on from cold I'd imagine the total current drawn will likely EXCEED 30A for perhaps a couple of seconds, until the elements begin to heat up (which they should do very quickly - although if outer sleeves of the plugs don't glow visibly for perhaps 5, 6, 7 or so seconds).

It can't hugely exceed 30A tho' even for a short time 'cos the fuse would definitely blow. So, let's take 30A as a 'max' to work on. 30A divided by 4 plugs means that each draws 7.5A. The cold resistance of each plug must therefore be in the order of (Volts divided by Amps) 12/7.5 = 1.6 Ohms.

That's a ballpark figure, of course, but I certainly wouldn't expect the resistance of a plug to be much lower than that at any time, and it'll increase to - ooh - 5 ohms-ish? when hot. (If each resistance was 1 Ohm, for example, the total current drawn would be 48Amps. I'm pretty sure that's quite normal for some diesel vehicles, but I'm still influenced here by the 30A fuse people have mentioned, so I'm guessing the Bongo's is less than this.)

So, can you measure the resistance of each plug? What are they? Any lower than, say, one ohm will likely be the cause of your problem, I suspect. At the very least, the values of all four should be pretty close to each other. I think this would be a really useful first test to make.

If your resistance scale isn't sensitive enough for this, you could try the 10A scale with your meter wired in series with a 12V supply as you feed each plug in turn - one plug at a time! Bear in mind that as soon as you connect the plug it'll start to heat and the current reading will fall. You want to try and catch a reading the moment it's connected. Mind you, there's a very good chance that your meter will over-read the split-second it's connected, and may even have an internal 10A fuse that'll blow! So, that decision is yours! The NGK website also say that you shouldn't connect a plug to an independent 12V source for any significant length of time as it could overheat inside.

I really think it's important to be certain what the cause is here.

[missfixit70]

TATM, the value of 0.5 ohm per glow plug already mentioned is taken from the manual, no need for speculation or guesstimation to muddy the waters As he's already measured the resistance as 2 ohms..........
Also as all 4 glow plugs resistances are in effect in parallel rather in series, how does this affect the calculation?

[westonwarrior]

all way over my head

however when I replaced mine with the fused link it ran for 24 months (ish) on a 30 amp spade fuse

[dave_aber]

4 plugs of 0.5Ω in parallel equates to 0.12Ω overall.

12v into 0.12Ω is 100A

So, I suspect that the 0.5Ω is only when cold.

To only draw 20A in use, the overall resistance must be 0.6Ω - 2.4Ω for each plug.

Hmmm......

[missfixit70]

So, I suspect that the 0.5Ω is only when cold.

......

Yup

[Trouble at t'Mill]

Missfixit, I hope I haven't muddied the waters!

As Dave points out, 0.5ohm across 12V would draw 24 amps - and that's just a single plug! 4 would be the best part of 100A. So surely even a slow-blow 30A fuse would be zapped by such a large current from such a low resistance? Ok, the resistance climbs very quickly as the plug heats up (and the element does heat up much faster than it would appear - it takes additional seconds for the outer tip to glow), but still...

All I'm trying to point out to eoptio is that he (she?) really must properly identify the actual cause, and I think the best way to start is to measure and compare all four plugs.