13 volts no amps?

Burnham Bob

Burnham Bob

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I have a jump start pack that I carry around on the boat in case I get a flat battery becuase there is no hand start on the diesel. My step daughter's car needed a jump start so when my wife was visiting they tried to use it. It didn't work. It was fully charged when I handed it over but they say it was almost flat the following day as it didn't start the car and took ages to recharge.

It also got broken along the way and the plastic handle on one one of the large crocodile clips was smashed. All in all not a success. However, now I have tested it, I'm getting 13 something volts on the meter after almost two weeks simce the last charge. For a fiver I've bought some new heavy duty crocodile clips and as soon as I can find my blow torch I'll solder the heavy gauge wires to the clips. (My soldering iron won't do the job as the big metal clips act as heat sinks.)

Now I need some advice. The unit says it should deliver 400 amps. Is it possible that its still reading 13 volts and holding its charge but can't deliver anything like the 400 amps promised which is why it wouldn't start the car? Or could there have been some operator error that discharged the unit without starting the car? (the boyfriend who broke the clip said it just came apart.............!)

Any suggestions as to how I might test the amps the battery pack can deliver? Having lost the instructions for the multimeter if I just put the probes onto the clips will it provide a load that then allows me to measure the amps? Dim recollections of school physices and v=ir suggest that i need some sort of resistance to measure the amps available.
 
Its possible to have 13v but little capacity. Did it turn the engine over albeit slowly? If yes, its not got enough grunt to spin the engine fast enough to start it. I've used one of these gadgets to start my yanmar once but most people don't rate the cheap ones. AFAIK, you can't measure the current with a simple multimeter.
 
The facts that it took a long time to charge as well as failing to deliver the amps required suggest that it might be an internal bad connection / high resistance
 
You can't get away from the fact that at the heart of the pack is a SLA (lead Acid Battery) The battery must be small to make the thing portable and inevitably small batteries mean small power. Either small in capacity or small in Cranking amps or likely both. These things can when good have a role in assisting a bad car or boat battery to get the engine cranking. I doubt especially in winter if they could ever do a stand alone start.
Then lead acid batteries are very susceptible to abuse. So don't like being left not fully charged. They self discharge over months. The SLA types are also very easily damaged with over charge. Lead acid batteries need to be used charged and partially discharged often. They are not suitable for keeping for emergencies. What is really important if you do have one is to keep a label on it recording last charge and last test. For most of us the months and years slip by so quickly. ou would be lucky under ideal coditions to have it last 4 years.
Indeed for that role a stack of eight D cells like Duracell or perhaps several stacks will give quite a few amps but best have a long shelf life.
So IMHO for a boat a proper dual battery system where the second battery is regularly charged and regularly used to start the engine (on its own) is going to be far more reliable than a tiny jump pack. Likewise for a car jump start another car with engine running is your best bet.
For the OP the best test will be a largish powered headlight globe connected across the output. The wattage will reflect the current drain. You should hopefully get 3 or 4 amp hours out of the battery before it goes low. (If it is a good battery) That assuming the battery is around 10 amp hours rated. good luck olewill
 
Being a belt and braces type, I already have a domestic and starter battery set up. THe battery pack is an emergency stand by as if I can't start the engine everything electrical fails. (Mind you I have a battery powered gps and hand held radio so you can see the paranoia and desire for back up doesn't just cover starting the engine.)
 
I have just replaced the battery in my jump starter / air compressor box (> 10 yrs old).
It was a 17ah battery, replaced with a 20ah one with same footprint for £30. The battery has nut and bolt terminals.
Re battery test, take it to any small garage and ask them to do a discharge test on it, they should have the kit.
 
LadyInBed said:
I have just replaced the battery in my jump starter / air compressor box (> 10 yrs old).
It was a 17ah battery, replaced with a 20ah one
Click to expand...

Some are much smaller. A quick look at a few specs revealed them as low as 7 Ah
 
I carried a spare (known good) car battery in a locker on my long trip as well as the usual house and engine batt set up. I did check the volts from time to time. Much more capable and a third of the price of a booster like the ones in Aldi this week.

I agree with what's been said already about small SLA devices. They always seem dead when needed a second time possibly years later.

A bodger's way of testing a starter battery is to connect jumps and, away from the battery, stroke the clamps together. You get a feel for the CRACK or fzzz you get. (don't try this at home folks...)
 
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Perhaps it's just the one I've got, but don't they require there to be a voltage on the circuit that is being boosted, and won't connect the jump leads unless there is? I think it's to prevent their being connected to a short circuit. I may have got this entirely wrong!
 
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