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A fairly common question asked here, and one that seemingly few people have a grasp of, opening up the likelihood of them being shafted by their local 'friendly' garage, so if I may, I'll try to remove some of the confusion.
The charging system and batteries are very easy to check with a basic multimeter or voltmeter available cheaply from Maplin. This will do fine, for £8 you really should have one.
So, basically, a quick and dirty check of your batteries. After the truck has stood for a while (overnight for instance) measure the volts at the battery terminals. It should be at or slightly above 12V. Stick your lights on, The voltage shouldn't drop significantly. This is a quick and dirty method. A specific load and a specific voltage drop is more accurate, but this will give you an idea.
Right, your batteries are going flat overnight and the garage want to sell you an alternator for £300. It is FAR (really, far-far even!) more likely to be the batteries are shagged and wont hold charge. To check, start the engine and switch in 'idle up'. Check the voltage at the batteries. It should be approximately 14.4V. little bit over or under is OK. Stick your lights on. Once again, the voltage shouldn't change much. If this is so, your alternator is fine. You can also try switching on everything you can find step by step, and check your voltage holds up under maximum load.
Another way of doing this for those more au-fait with electrical systems is to use a current clamp like this on your main battery +ve, start the engine and note the sign of the current flow (it will be +ve or -ve depending which way round the clamp is). Now start adding load, noting when (or if) the sign changes. This is the point at which you'll start to drain your battery, so keep the load under this amount, you power hungry maniac! Lots of huge spot lamps or enormous stereos can do this.
Hope this is useful - it's certainly not hard, or expensive.
The charging system and batteries are very easy to check with a basic multimeter or voltmeter available cheaply from Maplin. This will do fine, for £8 you really should have one.
So, basically, a quick and dirty check of your batteries. After the truck has stood for a while (overnight for instance) measure the volts at the battery terminals. It should be at or slightly above 12V. Stick your lights on, The voltage shouldn't drop significantly. This is a quick and dirty method. A specific load and a specific voltage drop is more accurate, but this will give you an idea.
Right, your batteries are going flat overnight and the garage want to sell you an alternator for £300. It is FAR (really, far-far even!) more likely to be the batteries are shagged and wont hold charge. To check, start the engine and switch in 'idle up'. Check the voltage at the batteries. It should be approximately 14.4V. little bit over or under is OK. Stick your lights on. Once again, the voltage shouldn't change much. If this is so, your alternator is fine. You can also try switching on everything you can find step by step, and check your voltage holds up under maximum load.
Another way of doing this for those more au-fait with electrical systems is to use a current clamp like this on your main battery +ve, start the engine and note the sign of the current flow (it will be +ve or -ve depending which way round the clamp is). Now start adding load, noting when (or if) the sign changes. This is the point at which you'll start to drain your battery, so keep the load under this amount, you power hungry maniac! Lots of huge spot lamps or enormous stereos can do this.
Hope this is useful - it's certainly not hard, or expensive.
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