The first part is easy, what is the max size of your alternator or charging device, i.e. do you have an 90 amp alternator or a 100 amp battery charger charging the primary battery bank. This means that the secondary battery could be subjected to at least that load so the relay must be able to comfortably handle that sort of current continuously. It would be wise to give the relay a good 10-20% comfort zone, i.e. always up size the relay if the charging source and relay are the same, for example, if you have an 80 amp alt and a 80 amp relay then go to the 160 amp relay option to be safe.
Next its cost of installation and ease of installation. If you are fitting the unit and access to ignition feeds is simple then the system should be entertained, however if not then the version is much simpler to fit and totally automatic.
The last but most important aspect is safety. The most important thing here is to establish what the maximum possible load that could be placed on the secondary battery bank when the relay is engaged, i.e. a large inverter/anchor winch, bow thruster. Remember what every load you put on the secondary battery will have a % of this load transferred to the primary battery depending on how full the secondary battery is. This could range from a few percent to 100 percent, so it’s important that the relay system can deal with this high load without damage. If there are large potential loads such as hundreds of amps then the only way to do this is using a because when exposed to excessive currents, the current limiting models simply and safely shut down until the excessive current is removed, i.e. switched off, then it can automatically re instate itself and carry on after that large surge load has stopped.
For stockists the best unit is the as this is 12 and 24 v with auto selection and fully adjustable which means one unit fits all.
Technical information
- D/C voltage : 24
- Amps : 50
- Size L x W x D mm : 140 x 60 x 40
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