{"product_id":"mastervolt-gmdss-battery-charger-monitor-500a-shunt","title":"Mastervolt GMDSS Battery and Charger Monitor, 500A Shunt","description":"\u003cp class=\"nvn-hero\"\u003eThe Mastervolt GMDSS battery and charger monitor keeps a constant eye on your DC power system, showing battery and charger status on a clear LCD with dedicated alarm LEDs. It reads 12 and 24 volt systems through a 500 amp shunt, and it flags DC voltage, charger, and AC mains problems before they leave you in the dark.\u003c\/p\u003e\n\n\u003cdiv class=\"nvn-description\"\u003e\n\u003cp\u003eOn a boat that carries a GMDSS radio installation, power isn't optional. The Global Maritime Distress and Safety System has to stay alive when everything else fails, and that means somebody has to watch the batteries and the charger that feed it. That's exactly what this Mastervolt unit does. It monitors the status of both the battery and the battery charger on 12 to 24 volt DC systems, and it puts the whole picture on a single LCD display with integrated status LEDs right where you can see it.\u003c\/p\u003e\n\u003cp\u003eThe panel gives you three separate alarms, and each one tells you something different. The DC voltage alarm warns you when the battery bank is sagging toward trouble. The charger alarm flags a charger that's stopped doing its job. And the AC mains alarm lets you know when shore or generator power has dropped out. Each alarm drives its own LED, so you're not decoding a single blinking light to work out what went wrong. On a commercial vessel or a larger cruiser running under GMDSS rules, that layered warning is the difference between a quiet fix at the dock and a dead radio when you need it most.\u003c\/p\u003e\n\u003cp\u003eAccurate current readings come from the included 500 amp shunt. The shunt sits in the negative side of the battery circuit, and every amp going in or out of the bank passes through it. That's how the monitor knows what's really happening instead of guessing from voltage alone. For the install to read true, route the negative cable cleanly to the shunt and keep other grounds off it. Parallel ground paths are the number one reason a shunt reads a little off, and on a 24 volt bank a sloppy ground can throw the numbers by a noticeable margin.\u003c\/p\u003e\n\u003cp\u003eA few things worth knowing before you mount it. On a steel or aluminum hull, isolate the shunt from the structure so you don't set up a galvanic path through the mounting hardware. Pick a spot for the display where you'll actually look at it, and keep in mind that any LCD washes out in hard direct sun, so a shaded corner of the panel or a small visor keeps it readable at midday. The unit ships with its top cover, the C1E, so the face is protected once it's in place.\u003c\/p\u003e\n\u003cp\u003eThe charger alarm works best with a charger that puts out a proper status signal, which most modern three-stage units do. If you pair it with an older charger that has no status output, expect the charger alarm to behave differently, since it can only report what the charger tells it. This is gear for boats that take their power seriously. Think commercial workboats, offshore cruisers, and yachts with a GMDSS radio station, where a battery or charger fault is something you want to catch early, not discover in an emergency. For a working boat that stays away from the dock for days at a time, knowing the charger is actually keeping up is worth its weight.\u003c\/p\u003e\n\u003cp\u003eOne more practical note. Because it handles both 12 and 24 volt systems, the voltage alarm setpoints are worth checking if you ever move the monitor between banks of different voltage. The thresholds that make sense for a 12 volt bank aren't the same ones you want on a 24 volt bank, so set them for the system it's actually watching.\u003c\/p\u003e\n\u003cp\u003eMastervolt has built marine power systems for decades, from towboats to luxury yachts, and this monitor fits right into that world. It's straightforward gear that does one job well. It watches your power and your charger, and it tells you the truth about both. Wire it in, calibrate the shunt, and you've got a clear read on the system that keeps your electronics and your safety radio alive.\u003c\/p\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eKey Features\u003c\/h2\u003e\n\u003cul class=\"nvn-features\"\u003e\n  \u003cli\u003e12 to 24 volt DC operation, so one monitor covers both common marine battery bank voltages.\u003c\/li\u003e\n  \u003cli\u003e500 amp shunt included, giving true current readings in and out of the bank instead of a voltage guess.\u003c\/li\u003e\n  \u003cli\u003eLCD display with integrated status LEDs, so battery and charger condition reads at a glance.\u003c\/li\u003e\n  \u003cli\u003eDC voltage alarm warns you before the bank sags into trouble.\u003c\/li\u003e\n  \u003cli\u003eCharger alarm flags a charger that has stopped doing its job.\u003c\/li\u003e\n  \u003cli\u003eAC mains alarm signals a loss of shore or generator power.\u003c\/li\u003e\n  \u003cli\u003eGMDSS interface built for the radio power that has to stay alive in an emergency.\u003c\/li\u003e\n  \u003cli\u003eTop cover (C1E) included to protect the panel face once it's mounted.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cdiv class=\"nvn-trust\"\u003e\n  \u003ch2\u003eWhy Buy from NVN Marine\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eAuthorized Mastervolt reseller, full manufacturer warranty\u003c\/li\u003e\n    \u003cli\u003eNMEA member and ABYC certified, advice from real boat techs\u003c\/li\u003e\n    \u003cli\u003eSame-day shipping before 3 PM ET on in-stock items\u003c\/li\u003e\n    \u003cli\u003eNY headquarters and Fort Lauderdale flagship retail store\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cdiv class=\"nvn-faq\"\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat does this Mastervolt monitor actually watch?\u003c\/summary\u003e\n    \u003cp\u003eIt tracks the status of both your battery and your battery charger on a 12 to 24 volt DC system, and shows it on the LCD with status LEDs for DC voltage, charger, and AC mains.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat is the 500 amp shunt for?\u003c\/summary\u003e\n    \u003cp\u003eThe shunt sits in the negative side of the battery circuit so every amp in or out passes through it. That's how the monitor reads real current instead of estimating from voltage.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDoes it work on both 12 volt and 24 volt systems?\u003c\/summary\u003e\n    \u003cp\u003eYes. It handles 12 to 24 volt DC. If you move it between banks of different voltage, check the voltage alarm setpoints so the thresholds match the system it's watching.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat alarms does it give me?\u003c\/summary\u003e\n    \u003cp\u003eThree. A DC voltage alarm for a sagging bank, a charger alarm for a charger that's quit, and an AC mains alarm for lost shore or generator power.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat is a GMDSS interface and do I need one?\u003c\/summary\u003e\n    \u003cp\u003eGMDSS is the Global Maritime Distress and Safety System. Commercial and SOLAS vessels carry a GMDSS radio that has to keep working in an emergency, and this unit watches the power feeding it. If your boat runs under GMDSS rules, that monitoring matters.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDoes it come with a cover?\u003c\/summary\u003e\n    \u003cp\u003eYes. The unit ships with its top cover, the C1E, so the panel face is protected once installed.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eHow should the shunt be installed?\u003c\/summary\u003e\n    \u003cp\u003eMount it in the negative battery circuit and route the negative cable cleanly to it. Keep other grounds off the shunt, because parallel ground paths are the most common cause of a reading that's slightly off.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eCan I read the LCD in direct sunlight?\u003c\/summary\u003e\n    \u003cp\u003eLike any LCD, it washes out in hard direct sun. Pick a shaded spot on the panel or add a small visor and it stays readable through the middle of the day.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhy does my charger alarm stay lit?\u003c\/summary\u003e\n    \u003cp\u003eThe charger alarm depends on a status signal from the charger. Most modern three-stage chargers send one. An older charger with no status output can leave the alarm behaving differently, since the monitor can only report what the charger tells it.\u003c\/p\u003e\n  \u003c\/details\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003ctable class=\"nvn-specs\"\u003e\n  \u003ctbody\u003e\n    \u003ctr\u003e\n\u003cth\u003eTitle\u003c\/th\u003e\n\u003ctd\u003eMonitors Status Of The Battery And Battery Charger 12 To 24 Volt DC; LCD Display And Integrated Status LED Indicators For DC Voltage Alarm\/ Charger Alarm And AC Mains Alarm; With 500 Amp Shunt\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003ctd\u003eMastervolt\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eManufacturer Part Number\u003c\/th\u003e\n\u003ctd\u003e21709150\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eUPC\u003c\/th\u003e\n\u003ctd\u003e816882022784\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eSystem Voltage\u003c\/th\u003e\n\u003ctd\u003e12 to 24 Volt DC\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eDisplay\u003c\/th\u003e\n\u003ctd\u003eLCD with integrated status LEDs\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eShunt Rating\u003c\/th\u003e\n\u003ctd\u003e500 Amp\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eDC Voltage Alarm\u003c\/th\u003e\n\u003ctd\u003eYes\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eCharger Alarm\u003c\/th\u003e\n\u003ctd\u003eYes\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eAC Mains Alarm\u003c\/th\u003e\n\u003ctd\u003eYes\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eMonitored\u003c\/th\u003e\n\u003ctd\u003eBattery and battery charger status\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eInterface Type\u003c\/th\u003e\n\u003ctd\u003eGMDSS interface\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003ctr\u003e\n\u003cth\u003eIncluded\u003c\/th\u003e\n\u003ctd\u003eTop cover (C1E)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@type\": \"FAQPage\",\n    \"mainEntity\": [\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What does this Mastervolt monitor actually watch?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"It tracks the status of both your battery and your battery charger on a 12 to 24 volt DC system, and shows it on the LCD with status LEDs for DC voltage, charger, and AC mains.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What is the 500 amp shunt for?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"The shunt sits in the negative side of the battery circuit so every amp in or out passes through it. That's how the monitor reads real current instead of estimating from voltage.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Does it work on both 12 volt and 24 volt systems?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Yes. It handles 12 to 24 volt DC. If you move it between banks of different voltage, check the voltage alarm setpoints so the thresholds match the system it's watching.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What alarms does it give me?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Three. A DC voltage alarm for a sagging bank, a charger alarm for a charger that's quit, and an AC mains alarm for lost shore or generator power.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"What is a GMDSS interface and do I need one?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"GMDSS is the Global Maritime Distress and Safety System. Commercial and SOLAS vessels carry a GMDSS radio that has to keep working in an emergency, and this unit watches the power feeding it. If your boat runs under GMDSS rules, that monitoring matters.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Does it come with a cover?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Yes. The unit ships with its top cover, the C1E, so the panel face is protected once installed.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"How should the shunt be installed?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Mount it in the negative battery circuit and route the negative cable cleanly to it. Keep other grounds off the shunt, because parallel ground paths are the most common cause of a reading that's slightly off.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Can I read the LCD in direct sunlight?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"Like any LCD, it washes out in hard direct sun. Pick a shaded spot on the panel or add a small visor and it stays readable through the middle of the day.\"\n            }\n        },\n        {\n            \"@type\": \"Question\",\n            \"name\": \"Why does my charger alarm stay lit?\",\n            \"acceptedAnswer\": {\n                \"@type\": \"Answer\",\n                \"text\": \"The charger alarm depends on a status signal from the charger. Most modern three-stage chargers send one. An older charger with no status output can leave the alarm behaving differently, since the monitor can only report what the charger tells it.\"\n            }\n        }\n    ]\n}\n\u003c\/script\u003e\n","brand":"Mastervolt","offers":[{"title":"Default Title","offer_id":44788452098141,"sku":"2007435","price":499.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0299\/7266\/0317\/files\/ImageServerAPI_83a9ca58-efd3-41eb-9b03-e3adcd279d91.jpg?v=1785021303","url":"https:\/\/nvnmarine.com\/products\/mastervolt-gmdss-battery-charger-monitor-500a-shunt","provider":"NVN Marine","version":"1.0","type":"link"}