Jump starters are devices that enable one to 'jump start' the internal combustion engine, when the main battery (or battery bank) fails.
Regardless if it is boat, car, lawn mower, forklift, truck or any similar vehicle, jump starters can be of great help.
Jump starters come in various sizes and shapes, with many different features and options. When buying right jump starter, there are few very important things to consider.
Jump Starter Maximum Current
This is practically the most important characteristic of any jump starter. If the maximum starting current of your engine is larger than maximum current of your jump starter, not only that you will not be able to start the engine, but you can damage your jump starter.
Fortunately, most modern jump starters have smart controllers that protect jump starter from being damaged.
If your main boat or vehicle battery is discharged and maximum engine current is larger than jump starter maximum current, it is possible to connect the jump starter to the battery and let the jump starter 'refresh' your battery. Transferring 5-10 Ah to the main battery can refresh it enough to be able to start the main engine.
Maximum current of jump starter is given in the Amperes (hundreds, sometimes even thousands), but often manufacturers state recommended maximum size (in liters, or cubic inches or centimeters) of the gas and/or diesel engine. Personally, amperes more accurately present peak jump starter power, but if you are not sure about your engines maximum starting current, at least you know its size, right? :)
Nonetheless, when buying jump starter, be sure that its maximum current is larger than maximum boat/car starting current. Since jump starters with maximum current of thousands of amperes are available on the market, at acceptable price, don't go cheap on them.
Jump Starter Safety Features
Modern jump starters come with all necessary safety features to help their safe use. If they don't have these features, no matter how cheap they are, don't buy them - jump starters provide large currents that can cause serious injuries (or worse) and can cause fire and other damage.
The most important safety features are:
- over-current or overload protection - if the main engine starting current is too large, it can damage the jump starter. When certain current is reached, jump starter's controller simply cuts off power - in order to try again, one has to either reset the jump starter or just try again to start the main engine. If the jump starter constantly shuts off, stop doing whatever you are doing even if the jump starter is fully charged and has maximum current far larger than the starting current of your main engine - there is some other problem (or problems) in your electric/electronic system which prevents starting the engine.
- short-circuit protection and reverse hook-up protection can prevent serious accidents. Short-circuiting or reverse hooking-up of jump starter cables can produce insanely high currents that can weld the cables and cause fire, damage, injuries or worse.
- over-discharge protection protects the jump starter battery from being over-discharged. Over discharging of any battery is not the recommended and can shorten the battery's life span. This is very important for jump starters that are used not only as jump starters, but also as auxiliary power source for charging laptops, tablets, smartphones and similar. If you do have need for auxiliary power on the regular basis, consider buying Marine Power Center for charging laptops, tablets, flashlights and similar and keep a fully charged jump starter as a reserve - and be happy if it is 'waste of money'! :)
- over-charge and over-voltage protection protect jump starter battery from being damaged by being overcharged. If the voltage is increased over safe level, gassing can occur, battery temperature can rise, causing fire and similar. Hence, many jump starters monitor temperature of the internal battery during discharging and especially during charging.
Other safety features include power surges protection (often part of short-circuit protection), rain/humidity/water protection, impact protection and similar.
In any case, good jump starter must have these safety features and by having them, don't be careless when using jump starters - they produce large currents, that can cause serious damage and injuries and that is why they MUST have these safety features.
Jump Starter Capacity
Jump starter capacity determine the number of possible jump starts on the single charge. Number of jump starts vary, but a good jump starter should be able to start internal combustion engine at the maximum current at least 10-20 times.
Capacity of the internal battery is important, but also the battery chemistry. Most modern jump starters use lithium batteries that are able produce large, fade-free currents from relatively small batteries.
Typical jump starter lithium ion battery has 15-20 Ah, but can be much larger if the jump starter is designed for trucks and heavy equipment.
Lead-acid batteries are not common in modern jump starters due to their weight and loss of power and capacity at high discharging currents.
Jump starters have analogue and more often digital meters that measure state of the internal battery and present it to the user. More advanced units can monitor line currents of the charged devices, to avoid any potential issue with the battery.
In order to produce versatile units, jump starters may be equipped with onboard air compressors (for inflating tires, dinghies and similar units), flash lights, USB charging ports and similar.
Again, although it is good to have such a versatile unit, don't forget the main purpose of these units - jump starting the main engine in the case of emergency. If the jump starter's onboard battery is discharged because of various gadgets connected to the unit, you can NOT rely on it.