T-Pain Is On A Boat: Re: [Electric Boats] battery bank question

Tuesday, February 16, 2016

Re: [Electric Boats] battery bank question

Thanks for your comments.

Cells under 5 volts are easy to manage because a computer can sense the voltage of anything under 5 volts. Over 5 volts and you need a voltage splitter so the computer can interpret the new voltage under 5 volts.

Our plus system uses a single battery charger for each 12 volt battery. Each battery charger measures voltage and temperature and reports this to a network where it is displayed. Charge Enable and Charge disable relays are controlled by each battery charger that sends a signal out if anything is out of range. Adding charging at 48 volts is done by enabling based on every individual battery's health. This enables high power hybrid operation as well as solar or additional 48 volt chargers. The chargers we use are small 25 amp chargers. It is really nice having this setup. If one battery fails you can replace just that battery and not the whole pack. Everytime a battery is charged it gets the exact treatment that the individual battery needs not an average of all batteries in the string. This greatly extends the life of the battery pack. It costs about $2,500 for the entire system, 4 chargers, 4 temp sensors, network display and shunt, but sure it is worth it if you prolong the battery life by years.

Now lets look at the 6 volts. Firstly if you could have the same trick of having the charger work double duty as a monitor that would be great but now you have 8 chargers on board.

Let me in on any fully automated system that balances the 6 volts without being overly cumbersome or complicated or with many wires all over the place. Remember to properly manage a battery you need to know battery temperature so with the 6 volts it does get much more complicated.

Pure Lead Batteries do not short their cells so can be combined in strings or at the battery level. It really doesn't matter but we recommend paralleling at the battery level and temp monitoring on a solid negative busbar which will give an average of the two battery temperatures.

With respect to any paralleling of Lithium or other lead batteries it should be done only at the cell level. You can't really go wrong at the cell level and I believe this is how Tesla does their builds.

If you parallel at the string level the cell that fails gets subject to string level voltage which is not safe. Lithium installers like paralleling at the string level because it is the only way to monitor each and every cell in the pack. But this does not make the installation safe or reliable.

Ordinary Lead, AGM, or Gel Battteries should not be paralleled at all. if one battery shorts a cell, then it will go thermal if in parallel with another battery, and this is made much worse if there is a charging source present. Add Murphy's law into the equation and the temp sensor will probably be on the wrong battery or totally nonexistent. The dead battery will draw current from the charger which now thinks the short is a house load.

I've seen lots of batteries blow up, once right in front of me. Until you do, you might not take these words seriously.

If you think that battery management is not necessary, then you have lots of money to replace your batteries prematurely, you have a good insurance policy and don't care about your boat, or you haven't gone down to your local battery supplier and check out the old batteries that are coming in the back door. Most batteries don't look so good after they have failed.

Battery Management is the most important safety tool aboard an electric boat next to AC management. If you don't have active battery management then the responsibility is with the boat owner to manually manage the batteries. This in most cases is overlooked and the batteries die prematurely, the customer is not happy and word is not spread about how good electric boating can be.

James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103

805 455 8444

james@electroprop.com

www.electroprop.com

On Feb 16, 2016, at 12:19 PM, 'Myles Twete' matwete@comcast.net [electricboats] wrote:

James said: "We typically do not recommend 6 volt batteries because there is no way to manage them"

What do you mean by this exactly? Maybe you're meaning something different than I'm hearing you say, but 6volt batteries in my estimation are easier to manage than 12v. Sure, you need more external battery interconnects, but when it comes to battery management, it matters little whether you're managing it at the 6v or 12v level---either can be multi-stage charged and either can be given an equalization charge. For many years, the most common battery of choice in EV conversions (and golf carts) was the 6v golf cart battery---tried and true. There are battery balancers available for them and one can even make a simple diode/bulb passive bypass balancer. Until Hawker AGM, then lithium options appeared on the scene, many if not most EV conversion folks raced EVs used 6v batteries.

As for the safety of paralleling batteries, I don't think even the pure lead batteries are technically safe. If paralleling lithium cells is considered patently unsafe, then there are a lot of TESLA, THINK and other cars on the road (a much more stressful dynamic environment than a boat) with paralleled cells & strings that are at high risk---didn't the Tesla Roadster lithium pack actually consist of individual cylindrical lithium cells tack welded as a 12P config or so? It is a concern---I'm still nervous about my current arrangement of the 21kwh of Enerdel cells on my boat in a 7P(2P(12S2P)) 48v arrangement. The Enerdel batteries themselves are 12S2P. Ultimately soon I will have all the fusing in place that will at least ensure that if one of the 12S2P should short a cell, a local fuse will blow isolating the rest of the pack from high rate discharge into that battery string.

YMMV-

-MT

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Tuesday, February 16, 2016 8:53 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] battery bank question

Hi Dominic,

Thanks for your inquiry. We typically do not recommend 6 volt batteries because there is no way to manage them. Over time, all batteries go our of balance and if this becomes significant it will ruin the battery bank and you would have to replace all of them at the same time.

We recommend Pure Lead Batteries. These batteries can be paralleled. We do not recommend any other type of battery to be paralleled for safety reasons.

Locating the batteries in different positions on the boat is no problem. You will want to run the positive and negative cables in the same bundle on the way to and from the remote battery to prevent any Electro Magnetic Interference with compasses etc aboard the boat.

The Electroprop Sailor is perfect for a Tartan 30C.

Let me know if I can be of any further assistance,

thanks,

James

James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103

805 455 8444

james@electroprop.com

www.electroprop.com

On Feb 16, 2016, at 7:53 AM, philip.l.probert@gmail.com [electricboats] wrote:

I have a Tartan 30C that I'm converting to electric. I've removed the old A4 and am in the process of modifying the engine compartment for the the batteries. The problem is that, however I configure things, all of the batteries are not going to fit in this space. Right now, I have a plan to use 6V batteries for my 48V system but one or two batteries would need to be placed in a different location. The total distance (cable run) away would be about 50". With the proper size cable, is this acceptable? Thanks for any help.

Also, if anyone has any experience with a Tartan 30 electric conversion I'd love to know what prop you're using.....