#1 Charging and battery options - Current State

During our few cruises this summer Windstar clearly lacked adequate electrical capacity for 2-3 days at anchor.  Subsequent investigation revealed 2-year old lead acid batteries at end of life, and an alternator ill-suited to rapid recharging of a deep-cycle bank.   This triggered an assessment of required battery capacity and charging options to support it.  (Note- the lead acid batteries later tested as new- I simply did not have enough capacity)

 

This is the first of four posts quantifying Windstar's energy usage and capacity, and defining what is required in an upgrade.   

How much energy is consumed?

See below for inventory of electrically-powered items, the power consumed by each, and a few use-case scenarios.  

Unsurprisingly, top consumers of power are 

• refrigeration -   4.3a at 30-75% duty cycle.   A constant  1.5-3ah -   
• Instruments- periodically 1.2-2ah with chartplotter and autopilot in heavy use.  (this range is an estimate.  See below for an empirical measurement of approximately half that value in actual use, in near-perfect conditions.)   
• Running Lights - The bow and stern lights are original, and consume approximately 17ah on an overnight sail.   (!)

Measured consumption

• In mild conditions, with autopilot set on leisure mode, monitoring the ICOM m506 VHF (.5a) and using basic instruments (without the chartplotter .45a) the power consumed was a surprisingly frugal 1.2 ah/hr.   
• Measured over approximately 36hrs at 25deg C ambient, the refrigerator consumed 1.6a/hr or 38.4ah/24hr.  This is a 37% duty cycle.  I believe that power consumption increases disproportionately as ambient temperature rises.

Observations:

• The Evolution Autopilot uses much less power (and is less noisy and obtrusive) when in leisure mode than in performance mode.   (.25a/h in a recent test, minor and infrequent course correction) 
• While at anchor, VHF can be monitored by the handheld.
• The propane solenoid (1a) uses a surprising amount of electricity.
• Non-LED running lights consume significant power and should be replaced.
• If not required, the chartplotter could be turned off and viewed periodically to update position.
• Even after improving its insulation and sealing, the refrigerator consumes, nearly 80% of the electricity used while at anchor, more in extreme heat.  Could this be reduced? 

Use-case extrapolations

For extended cruising, fresh and especially black water tank capacities, plus garbage disposal impose practical constraints.  In practice, Windstar can be independent of services for an extended  long weekend with two aboard before needing fresh water and a pump-out.   

Today's energy storage and charging capacity does not support a cruise of this length.     Approximately 150-200ah (usable) is a reasonable and conservative estimate of what is required.             

How much energy is actually available?

Battery Type

Windstar currently uses two group 31 Deep cycle flooded batteries rated at 110  a/h each.  Assuming a 50% DOD, she has a theoretical 110 a/h capacity.   There is a shortfall of 50-100ah of storage assuming batteries have their full 20hr rated capacity.

At the moment it is much less, with the SG reading 1225 on many of the cells. 

Battery Bank size - (Flooded type)

Usable capacity is a function of not only AH rating (size) but depth of discharge.  Deep discharges shorten battery life.  Therefore, for a given number of amp hours required, (aka - days off the grid) a battery bank should be the largest size practical in order to minimize the depth of discharge.  In evaluating battery types, I assumed a maximum DOD of 50%, 60% and 80% for flooded, AGM, and LiFePo respectively. 

Space, particularly height, is limited.   Additional weight has a disproportionate impact on a smaller lighter boat than on a larger one, so I am always mindful of this.

 I had thought that 2 group 31 batteries (60lb ea)  plus one start battery was Windstar's practical limit, however another 33-2 owner has advised that he was able to install 4ea group GC 6v (approximately 420 AH, and 280lb) golf cart batteries in the existing battery locker.    This surprised me, however I had not considered that AGM batteries need not sit upright.  4 batteries doubles the available capacity, but also doubles the weight and space.   Lithium batteries provide much greater capacity for a given footprint, and are half the weight of their lead-acid counterparts, but come at a substantial up-front cost.

Charging Systems

Alternator

Windstar's Yanmar 2GM20F drives a stock 50a Hitachi automotive type alternator  via a 3/8" V-belt.   

A 50a alternator has adequate output to charge the 240a bank of flooded type batteries, provided the regulator and associated protection circuits permit/manage the charge profile vs alternator load.     The stock alternator is not ideal for providing a well regulated high current charge to a deep cycle house bank, and I have observed the quick reduction of charge voltage under load as the alternator's thermal protection kicks in.  It seems to work well for extended runs at higher RPM, but I haven't quantified this the actual state of charge at the end of such a run.

Since Windstar is kept at a marina and her primary charging means is a 20a 3-stage shore power charger, All batteries are regularly receiving a full 3-stage charge, after only having been slightly discharged. This is ideal for long battery life.    For the way the boat is used, the stock alternator will probably suffice.  The current alternator/regulator would not be appropriate as the primary means of fully charging a depleted house bank.     

 Much is explained in this article.

  

An upgraded alternator and smart regulator would be required if the small diesel were to be considered as a  deep cycle charge source at anchor.  The constraint would then be the (small) 3/8" alternator drive belt, which might be taxed at full load, and a great deal of heat would be generated in the same spaces in which the refrigeration seeks to dissipate heat.

Shore Power Smart Charger

Windstar has an older Xantrex Truecharge 20+ charging both start and house batteries.   This charger can supply 3 different banks, but they must be of the same type.  (AGM, Gel, or flooded.)

Solar Option?

The 33-2 is a well-thought-out, compact, performance-oriented racer/cruiser, with above average creature comforts.  I am extremely reluctant to add weight, windage or appendages that might detract from her basic virtues.       

The photos below show the space available on the bimini.   It appears that I can fit approximately 150-160w  of solar panels, from which I can expect approximately 400-500w per day, based on a conservative rule of thumb of 3hrs rated output per day.   

 If accurate, this is just adequate to maintain the batteries while at anchor with the boat unattended and the fridge running at a 37% duty cycle.    (1.6ah X 12.5v X 24 hours=480w/24hrs).    At a 50% duty cycle the fridge uses approximately 2a/h @ say 12.5 v so 25w, X 24 hours = 600w/24hrs.    So in the hottest summer heat the house bank may still slowly deplete, unless the solar output improves at the same rate.

Regardless, the addition of solar generation significantly, extends the time between charges and appears to achieve goal of an extended long weekend without charging.    This is quantified in subsequent posts.  

I would likely mount the panel in the following manner:

https://marinehowto.com/installing-a-solbian-semi-flexible-solar-panel/

What does an upgrade look like?

For short summer cruises, approximately 150-200 usable amp hours is a reasonable house bank capacity.    More is better. Supporting this with thoughtfully-installed solar generation would make sufficient electricity available for how Windstar is used today, without adding excessive weight and clutter.   

 

The next post deals with evaluating battery and solar panel options.   Options are evaluated here.

To read more on this project click the label/filterwith the tag ‘solar and batteries’ on the right.