| Author |  Topic  | |
andydeans3
V4 Guru
United Kingdom
2016 Posts |  Posted - 25 Jul 2018 : 14:02:51  
| Attention all auto-electric gurus!
Does anyone have any idea of the rough current being drawn from the battery, with all electrics on, ie engine running, full beam headlights, heater fan full blast, radiator fan on, wind screen wipers on fast speed, and windscreen wash pump going?
My ammeter can only read maximum 10 amps, and I've got a feeling it's much more than that.
Andy
1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro |
Edited by - andydeans3 on 25 Jul 2018 22:32:12 |
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greg124
V4 Fan
United Kingdom
173 Posts | Posted - 25 Jul 2018 : 19:13:24
| Andy,
2x60W mainbeam + 2x5W tail lights + 2x5W front side lights + 2x5W number plate lights + 2W mainbeam indictor = 142W/12V = 12A
If you include brake lights & hazards that's another 128W = 10.7A
Early wiper motors quoted as 3A, from 1970 on 15W
Washer motor about 1A
Ignition about 3A
Instruments and their lamps, less than 1A
You would need to check the tech spec of your electric fan, as there can be quite a wide range of current draw on aftermarket items. Got a feeling the one I investigated, but never bought, for the Alvis was about 8A
A healthy alternator should provide about 13.8V, so the measured current drawn will be less than that specified at 12V
Hope this helps
Clive
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andydeans3
V4 Guru
United Kingdom
2016 Posts | Posted - 25 Jul 2018 : 22:31:44
| Greg
Thanks, mate, though I don't think brake lights and hazards would be 128 watts?
All in ball park figure perhaps around 25 to 30 amps perhaps?
Andy
1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro |
Edited by - andydeans3 on 25 Jul 2018 23:20:54 | |
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greg124
V4 Fan
United Kingdom
173 Posts | Posted - 26 Jul 2018 : 00:45:20
| Brake lights and indicators are 21W (unless you are using LEDs) bulbs each x6, plus I think 2W for the hazard flasher circuit, but indicators are only on about 50% of the time. I can't imagine a scenario when ALL the lights would be on...
According to my manuals a standard 96 alternator is rated at 35A, and it need's to put something back into the battery after starting. 30A-ish sounds about right.
Do you have a specific problem? or checking whether the numbers work for an upgrade?
Clive
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andydeans3
V4 Guru
United Kingdom
2016 Posts | Posted - 26 Jul 2018 : 10:07:55
| Clive
Friend of mine had a near disaster, with smoking wires on his MGB a wee while ago, and I'd like to fit some sort of a cut off switch (accessible from the drivers seat)into the heavy cable between the alternator and the top of of the fuse box.
I know you get these big heavy duty switches that you cut into the main battery cable with, but they're a bit big and cumbersome, to bring into the cab. I had something more discrete in mind, so need some idea of the maximum current it's ever likely to need to carry.
I've already got one of these Lucas switches on the left side of my steering column. It's not used at the moment.
It's good for 25 amps apparently, sounds like it might not be enough.
https://www.autosparks.co.uk/electrical-components/automotive-switches/lucas-ignition-switches.html
Andy
1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro |
Edited by - andydeans3 on 26 Jul 2018 10:10:46 | |
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greg124
V4 Fan
United Kingdom
173 Posts | Posted - 26 Jul 2018 : 21:53:49
| Sounds like a prudent modification Andy, but as you say, a beefier switch is required.
If I was doing this, I would go for one rated at least 10-15% more Amps than the output of the alternator.
Some of those battery cut-outs are rated at 500A so they need to be chunky
Clive | |
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andydeans3
V4 Guru
United Kingdom
2016 Posts | Posted - 26 Jul 2018 : 22:10:09
| Greg
Aye, the chunky ones rated at 500 amps need to take the current drawn by the starting motor turning.
I'll have a rake around to see if I can find something rated around 35 to 40 amps continuous.
Andy
1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro | |
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| | Topic | |
Total current drain with all electrics on?
