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How Do I? 35 amp alternator , will it do?


Extreme Landy Fan
i need to start my 19j on the week end and all i have is a 35 amp alternator , will this do to start it do you think?
so a 35 amp alternator will run ok on a 19j?
thats good news.
i was under the impression i needed a 45 amp.
cheers fellas.:)
so a 35 amp alternator will run ok on a 19j?
thats good news.
i was under the impression i needed a 45 amp.
cheers fellas.:)

if you need a 45amp then you need a 45amp.

The 35amp will charge the battery, but it *might* start to struggle when you have all the standard electrics running i.e heater blowing, lights on, wipers on, radio etc (winter night driving in the rain - worse case) then the battery is going to get less charge or might even drain. So you will have to run the engine longer else before long you will get a flat. This is not considering anything else you might bolt on, spot lamps, cb, amp etc Though I guess they build in a element of overkill to cater for mods like spotlamps and for an efficient charge rate.

*they* say for a healthy battery to regain its charge from the starting drain the alternator needs 20mins of running time.
I think you'll struggle with 35A if you have any electrical accessories, but if you keep the electrical loads down, it'll be OK. 45A is the standard 12/19J alternator capacity. 65A is the biggest available over the conter, though I wonder if a 200Tdi alternator would fit (I believe it has V belt pulleys too).
My 19J has an alternator on it, though I have no idea how well it works. It looks OK, and is probably the standard 45A. You can have it for £10, though it would probably cost as much again for postage - it might be best to get one from an auto electrcal shop (cheapest with a warranty).
cheers Nick.
im gonna try the 35 amp first to see how i get on with it.
thers a scrappy 5 mins down the road and i was going to try him for a sierra one as apparently they are a straight swap.
you could do the math if you wanted (maybe we can do a group effort here) to get a rough idea of margin when using 35amp. Add up all the expected current drain from each piece of equipment running in a worse case scenario. Add how much drain normal starting takes, and how long it will take to recharge that hit during worst case drain if possible at all (which may well under 35amp anyway). Maybe same math for normal driving, maybe without fan on, of full beam, or wipers and compare it.
there is a handy to use Alternator test tool for sale in Aldi for £2.99 this week, i've used one of these for years, it gives a fair indication of what the vechicle uses before the battery starts to discharge, but before the ign light comes on. Often in winter with only just a few amps to spare batteries suffer.
A 200tdi will fit on a TD, and visa versa. Some 200's are only 45 amp too though I believe.
35A will do for now if thats all you have, its better than nothing. Buy a 65A if anything, its better to have an overrated one so then if you want to run spots, you've got the extra power to play with. I run 720W of spots up front, as well as a cb and heater in the winter, windscreen wipers ect ect, can tell the difference the extra 20A makes. Its a lot for a 45A, probably why my old one died. I was waiting until it did so I could get a 65A:p
On a slightly different but at the same time same subject, am I right in thinking an ammeter tells you what you alternator is charging at, and a voltmeter tells you what voltage is in your battery? Thinking of putting an ammeter in mine (if what i said above is correct) because I do run alot of leccy stuff and would like to know that everythings ok!

Cheers, Ben
Well, all lights on at once (dipped beam, side, tail, brake, hazards, fog, reverse, not that you'd ever have all of them on at once!) would draw around 25A@12V.
Assuming an alternator output of 14.5V the current would theoretically drop to 21A.
Can't see the fan, wipers, shut-off solenoid etc using the remaining 10A. A heated rear window would probably cause a discharge though.
But seeing as you can get a new 85A of Ebay for around 50quid...........

I have a 19A dynamo on my old Series1. Never had a flat battery in the 15-odd years I've had it!

An ammeter tells you how much current you're using.
You could either connect it to alterantor output, and it'll show all loads including what the batteries are taking.
Or connect it between starter solenoid and ignition switch to monitor what loads you're applying.

Alternators are something Britpart do well at - they sell Denso alternators, which are OEM, and are good quality. In the BP box, they don't sting your wallet much. That's what I used for my 65A unit. Just so you know, the 45A type has the 3-bladed plug connector, but the 65A unit uses a stud for ring terminals on the harness.

Given the extra capacity, rather than cutting off the existing plug and crimping on ring terminals onto the (probably isufficient) original wiring, it might be best to run a pair of 50A cables from the stud straight to the starter solenoid in parallel to the existing wiring, so that you don't molest the standard harness and retain the option of fitting a 45 or 35 alternator if you have a failure and can't get hold of a 65 quickly. I did this with some cable ties to clip the new wires to the originals along the rhs of the head gasket and to hold the original connector block out of the way, and just made up a small wire with a ring terminal on one end and a spade connector on the other to conect to the alternator charge warning slot in the original connector block. It works perfectly.
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