wrnoof avatar image
wrnoof asked

Using Cerbo Gx & VRM logged data to design sailboat power upgrades

I am planning to upgrade our sailboat AGM batteries to LFP and expand our 200W solar array. We have a Quattro12/5000/220-2x100, Blue MPPT 100/30, Smart Shunt and a Cerbo GX installed. We have been logging the Cerbo data to VRM for several months. This historical energy data should be useful in sizing our new battery bank and solar array. Is there a good reference or instruction article on how to use the logged data for this purpose?

cerbo gxLithium Batterysystem designsolar sizing
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1 Answer
Sarah avatar image
Sarah answered ·

Hi @wrnoof if you haven’t read them already Energy Unlimited. and Wiring Unlimited are well worth the read.

Sizing a Lithium upgrade from AGM can be challenging as all the rules change. The biggest change is probably your usage patterns themselves - being unconstrained from AGM charge/discharge and state of charge limitations opens up a whole new way of using your boat - especially considering you have such a large inverter !!!

First to consider is what your discharge when the boat is unattended. Can your solar panels recharge the overnight usage (even after a couple of days of bad weather). We are a catamaran and have about 1.2 kw of panels. After changing from AGM to Lithium we could now leave our three fridges on 24x7 instead of having to move everything to one fridge when we leave the boat.

Next what are your big loads when you are onboard? How will you recharge these ? Solar/alternator/generator. Will the loads change? Big changes for us included using the water maker, kettle, and hot water. We have 600 A/H of Lithium and heating the hot water which takes about an hour can consume around 20% - we would never have considered doing this on our previous 1200 A/H AGM battery bank.

I would also consider what options you have for upgrading your alternator. Unless you have shore power/generator or are a catamaran like us, your solar panels will be limited and the alternator becomes your main source of power when under way. Special consideration should also be given to protecting your alternator but that is a different topic.

Writing this really reminds me that when sizing an AGM install the limiting factor is nearly always going to be the size and weight of the battery bank. For Lithium the limiting factor is money and the charging source. And as the saying goes ‘the more power you have the more you want’. I hope this helps.

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