![]() Typically shunts have a capacity of 500 amps, and will easily cope with the entire load from lights, electronics, fridge and so on. The ammeter connects across this and through that shunt it can measure how much current is passing in or out the battery. Determining how much current is passing through an electrical circuit requires an additional component called a shunt – a short piece of copper conductor with a known resistance. In addition, it can display the voltage of a start battery, so it’s perfect for most single or-dual battery setups.īecause the house battery requires monitoring of both voltage and current, installation gets a little more complicated. This single, round digital display monitors the voltage, current, battery capacity and amp-hours of the house battery. The entry-level product from the Mastervolt range is the Battman Lite, available from most chandlers. There’s quite a range and installing one is slightly more complicated than installing a simple voltmeter. I visited the experts at BEP Marine to explore the options. So after forking out $450 for a new battery, I wanted to try and prevent that expense happening again anytime soon – it was time to fit a battery monitor. In the case of my launch I discovered that by mid-winter my house battery was self-discharging within a matter of days, a good indicator that it was stuffed. It makes sense to protect and monitor the house battery to extend its life. It’s typically more expensive than a start battery. Which is why it requires a different (deep-cycle) type of construction. Size (capacity) is important because they often have to deliver the massive current a starter motor needs to turn over a cold engine.īut the house battery is charged and discharged continuously, and it works much harder. Because starting the engine usually only takes a few seconds, they’re rarely drained. Most dedicated start batteries last a reasonably long time, as long as they get the occasional top-up during the quiet season. It is the house battery which requires the most attention. A voltage-sensitive relay (VSR) switches charging to the house battery once the start battery is topped up. A second (house) battery runs all the onboard accessories. This is recharged by the alternator once the engine is running. It has a start battery, its sole purpose to provide high cranking amps for a few seconds to start the engine. On my launch I have a typical two-battery setup. You then know how long it will take to be fully charged or, if the engine is not running, how long before you run out of power based on the current drain from accessories such as lights, stereo or chartplotter. It can measure both voltage and current and, when pre-set with the capacity of your battery, it can also tell you the overall state of charge. And this is where a battery monitor is useful. What you need to explore is the current that’s flowing in or out of the battery. And while a higher voltage tells you that the engine is pushing power back into the battery, in itself it does not tell you how quickly it’s charging. If the water pressure is the volts then the volume of water is the current, measured in amperes (amps).Īnd so it is with batteries: a low voltage certainly indicates that you have a problem but it’s not much help for overall management of your battery. The flow dictates how quickly we can fill a bath, not the pressure. But the volume of water is more important when trying to fill a container, and the tap gives you control over that. Think of it like a water tap: The water in the pipe has a certain pressure, and as long as that’s neither too low nor too high we don’t worry much about it. But voltage is only a small part of the story. After all, it shows how many volts the battery is delivering and (when the engine is running) how many volts are going back into the battery. You may think the voltmeter tucked among the helm gauges is sufficient. ![]() Which is why a battery monitor is a good idea. Also, most batteries only provide a finite number of discharge/recharge cycles, so if you don’t know how many times the battery’s been charged you can’t judge it’s overall condition. Leaving the boat unused for long periods will undoubtedly result in self-discharge, but even a regularly-used boat can suffer from a flat battery if you ignore how much power is going in/coming out. You should never fully discharge any battery – over-discharge is said to be the single biggest cause of battery failure. The most important aspect of a long battery life is good management. Is it any wonder they often last less than three years? Norman Holtzhausen reckons their life could be more than doubled with better maintenance. ![]() On a typical boat, batteries are ignored, abused and unloved – and yet are asked to deliver maximum power at start-up.
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