Log in
Article search:

Q & A


We have bought a35 ft liverpool narrow boat with a 20hp beta.the handbook says it has a 20amp alternator.we have an electric fridge and no tv, is the alternator big enough or perhaps a solar panel would help to charge batteries.it seems ok up until now, about six months

Asked by: ken button  | 6.46pm, Thursday 23 October

WW says:

A 20 amp altnator seems small... Often a 40amp alternator is fitted- you should be able to see a rating plate (or serial number) and check the rating.
A 20 amp alternator should be able to support a maximum of around 220Ah of battery capacity on the domestic side (assuming the starter battery has a negligible charge requirement), given that you will run the engine (preferably cruising) 6 to 8 hours a day, you could expect 60 to 90 Ah of charge replenishment- which is enough to recharge an almost-discharged 200Ah battery bank (which, when almost empty is around 50% discharged).
A solar panel system will be useful to charging the battery system, but not generally at the same time as the alternator from the engine (although there is not real issue with it happening, you might, while the engine is running, not get that much useable charge out of the panels, depending on the charge controller).
let us know about your battery bank size, and other electrical loads (in addition to fridge), and if you are cruising every day or are mainly stationary, and we may be able to give more advice.
I hope that makes a good starting point.

Mark Langley  | 9.22PM, Thursday 23 October

Readers say:

Thank you. We have a starter and two leisure batteries. We are more likely to cruise for 5 or 6 hrs. I will check the out put of the alternator in the next few days.

ken button  | 4.23PM, Friday 24 October

You must log in to post an answer.