Re: [electricboats] How does the Curtis F4A controller calculate battery state of charge (SOC) ?

This sounds a bit misleading to me.

 

Yes, with lead acid and with some Lithium chemistries, particularly Lithium Ion, measuring voltage alone can give a good indication of SOC.  Having said that, the SOC does not indicate how many AmpHours remain.  I mean, the older and more sulfated a lead-acid battery set is, the more voltage alone does not tell you much at all.  Historically, EV conversion folks have used current monitoring via shunts and amp-hour estimation (e.g. using Xantrex Link-10) to track actual Amphours returned in charge and Amphours delivered in use.  It was really the preferred and reliable way to be sure how much actual "capacity" (vs SOC%) was available for a trip.  Many times I was disappointed to find that my "fully charged" lead acid pack would deliver far less than I expected, leading me to fire up my generator while underway on my boat.  Since going to lithium ion on my boat, voltage measurement alone is quite sufficient to inform how much capacity remains.

 

Having said all that, I think monitoring actual amp-hours absorbed and delivered is very good information to have.  You're in a boat, perhaps motoring downstream several miles, then up another branch of water or upwind or against tide and it's important to track capacity used so that you can estimate whether or not you need to slow down in order to have the capacity to reach the destination.

 

FWIW-

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Darin
Sent: Friday, June 21, 2024 8:15 AM
To: electricboats@groups.io
Subject: Re: [electricboats] How does the Curtis F4A controller calculate battery state of charge (SOC) ?

 

Lars, 

 

Battery voltage is usually used alone to calculate SOC for lead acid, which explains why you don't have a hall effect sensor.  Yes, I would say the BDI number is probably the same as SOC for this purpose.  I'm surprised to hear that Thunderstruck hasn't been helpful.  I've always had good support from them personally.  

 

Darin

 

On Thu, Jun 20, 2024 at 10:43 PM SVTwister via groups.io <yellowchair=gmail.com@groups.io> wrote:

I don't have a shunt or hall-effect sensor to measure current at the battery cable. The display is connected to the Curtis controller which does not have any auxiliary sensors. The controller measures current, which is one of the data the display shows, so it could use that to calculate amp-hours, or it could use the voltage which is another thing the controller measures and displays.

I have four 100 Ah, 12 volt lead-acid batteries, by the way (in series for 48 volts). I stated this when I ordered the kit from Thunderstruck a couple of years ago, so I am wondering if the controller was programmed for my battery bank and how it calculates state of charge. Thunderstruck does not want to or cannot answer these questions.