Re: [electricboats] Power in and out of battery bank

I first wrote about doing this back in 2005 or so.  I converted my boat to electric in 2003 www.evalbum.com/492 .

In 2005 I hauled it out and repaired bottom damage, etc, got it prettied up, then got it out on the river.  Then I did a 90 mile round trip on the Columbia River to the Cathlamet Wooden Boat Show.  With just about 300ah at 36v onboard, there's no way I could make the trip on shore power alone.  And I didn't think I'd be able to recharge at Cathlamet or anywhere else on the river.  So I brought some gasoline, a Honda EU2000i genset and 2 chargers.  Going downstream I realized that one of my chargers wasn't working, so I only had one running (generating just 20amps to the pack) going downstream.  To make time, I was probably cruising at 40amps.  And so, the pack saw a net loss of 20amps.  By the time we reached the boat show the pack was down about 150ah---and I couldn't recharge at the docks.  My wife brought me a spare charger and so, going back upstream I had 40amps of charge current.  If I was using just 40amps, the net current was zero and the pack voltage unchanging.  But to make it upstream at any rate, I used about 55amps.  After several hours of this, we rolled into a marina for the night (again, no charging available and didn't want to annoy folks with my genset) at this point maybe 230amp-hours down.  The next morning, things were still not ideal (bad tides) and so initially was still using power despite the genset and chargers.  But things improved and so it eventually was clear I'd make it back, barely---nearly 300ah used from the pack on the trip.  As I recall, the genset/chargers provided about 800ah on the trip.

 

Anyway, bottom line is you need to know your pack's state, what your genset/chargers are capable of and what power levels you'll need for your trip.  Plan it out and give yourself extra time.  The slower you can run the boat and make progress, generally, the less energy it will take to go the distance.  It's more complicated with current flow---i.e. with a 2kt current you wouldn't want to slow your motor to the point that you go 2kts on the water.  Still, do the calcs, bring the fuel, bring spare parts as needed and hope that your genset/charger keeps running.  Plan for contingencies for the case of those things failing---i.e. keeping enough pack energy to get to the next (or the last) harbor or perhaps having solar or wind power available---or cell phone and a wife who could bring parts J.

I like to power in and out of marinas (or towns) on just electric.  Knowing it's 4 hours at 3knots vs 3 hours at 4knots, needing to get to the destination in 3 hours dictates the faster rate---at least for the main part of the trip.

It's fun to watch the Amp gauge.  Start up the genset, plug in the chargers, watch 40amps going into the pack and seeing the bump in pack voltage is nice.  Then heading out, current drops as you pick up speed until the current direction flips.  If starting out, your pack is likely already full, so you either let the charger(s) respond to that or you'd want to increase boat speed to draw more current until the net current goes to zero or negative.

It's all pretty obvious really.

 

Enjoy.

 

-MT

 

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Thierry
Sent: Wednesday, September 27, 2023 11:25 PM
To: electricboats@groups.io
Subject: Re: [electricboats] Power in and out of battery bank

 

Just to clarify: you can!

There's no problem charging the battery and using the motor at the same time.

The only risk I see is that if the motor is regenerated (charged via the motor) and via a charger, the battery voltage may rise without "control", and even then... the charger will stop, and if the motor's speed controller is properly adjusted, regeneration will stop too!