Wednesday, June 7, 2017

Re: [Electric Boats] Feasible to change to 6v golf cart batteries?

 

Putting circuit breakers or fuses between parallel banks doesn't alleviate the dangers of parallel batteries.    It only takes 5 or 6 amps from one good  battery to the other paralleled failed battery to drive a short that will take the lead acid battery thermal.    This level of fusing does not allow for use of the battery at the currents required.   


The only way to safely put two batteries in parallel is to use Pure Lead technology.   Pure Lead fails open at the end of the battery life, and doesn't short it's cells.

The problem with AGM, GEL, or Flooded is they have 6 cells (in a 12 volt battery).    So if two batteries are in parallel, and one shorts a cell, the good battery is still at 12 volts, whereas the shorted battery is now effectively a 10 volt battery.    Electricity flows from high voltage to low voltage, so the good battery drives the short in the bad battery resulting in a thermal situation.    

On a 48 volt system, with two strings of 48 in parallel, if one string shorts a cell that string becomes 46 volts, and the other string stays at 48, and the good string drives the short in the bad string - and there is a lot more power behind it to make it go thermal.

I have seen a lot of posts mentioning series / parallel battery connections to get a larger battery bank and I am very concerned with the safety of these systems.     

If you are going to have two sets of 48 volt strings, then use them one string at a time.      Never hardwire batteries in parallel.   Never leave batteries in a parallel.   

The best solution is to stay with one battery string of pure lead batteries and if you need more energy, then go up in voltage to 60, 72, 84 or 96 volts.    Just be aware that higher voltage has other risks involved.   In the US, the safety threshold is 48 volts, after which you need to float the battery pack (battery negative is not tied to ground) and monitor for insulation resistance to ground.     There is no feasible way to look for a ground fault on a grounded battery which is why I prefer floating systems.    

The reason we choose Northstar over Odyssey, is the Northstar has a lower charging requirement.     The 200 amp hour Northstar can be charged at 20 to 25 amps, whereas the Odyssey requires 80 amps charge to get the advertised cycle life.   80 amps isn't realistic from shore power and requires a generator.

The general rule of thumb for any lead acid battery is the heavier you discharge the battery, the higher the charging current should be to desulphate the plates.    

So if you build a high capacity AGM / GEL or Flooded battery in series/ parallel, you won't have the charging current required to get the life cycle out of the battery.   The big battery bank will fail prematurely and you end up over time with a smaller capacity, more dangerous battery than if you had built a smaller battery correctly and charged it at a good rate of charge.   

It makes far better sense to spend money on monitoring / balancing and higher current charging, than it is to waste your money building a dangerous series / parallel AGM / Gel or flooded battery bank.      









 








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

805 455 8444

james@electroprop.com

www.electroprop.com

On Jun 7, 2017, at 8:12 AM, 'Jason (Electric Boats) Taylor' jt.yahoo@jtaylor.ca [electricboats] wrote:

 

I can certainly attest to this. Just not on my boat. I have a whole-house UPS setup that has 4 battery modules of 240vdc each, connected in parallel. 
Each module is 20x 12v 7ah SLA batteries connected in series. 
Each module has a 50a 4-pole circuit breaker, connected at 0v, 120v, 240v, and on a control line. 
I had two batteries short internally. This caused a the entire module to drain into the shorted cells, destroying 20 cells. 
It also caused the 3 other battery modules to drain into the short. However, as soon as the load passed 50a on the shorted module, the breaker tripped under load. It saved the 3 other modules but the breaker destroyed itself in the process. The UPS kept right on keeping on, without the shorted module, so with reduced running time. 

My basement filled with an acrid smell of sulfer and there was a it of haze in the air. This was from only two, small SLA batteries. Imagine the same situation happening in a smaller volume of a boat with much larger batteries, with more easily vented gasses and fumes. Not a fun place to be. This certainly highlights the need for circuit interrupters located at the power source. And also between parallel banks. The added costs of this very sane protection add up quickly so it's often better to fit a single large bank initially. 

/Jason


--
Jason Taylor
v:514-815-8204

On Jun 6, 2017, at 14:23, James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:

 

There is no way to monitor a 6 volt battery.


Batteries in series  go out of balance over time.    One of the batteries will go to a very high voltage, and the rest will be low.   The high voltage battery is at risk of gassing off and can experience catastrophic failure.  

Most of the danger comes at the end of the batteries life, but batteries sometimes fail prematurely.    A lead acid battery system should be monitored just like every Lithium system out there.

I do not recommend 6 volt batteries.   There are twice as many batteries in the system, so twice as many interconnections, and much more to go wrong with a system like this.

Batteries in parallel have issues too.   Hardwiring batteries in parallel is problematic.   when one battery fails, the other will be ruined by the failure.   In worst case scenarios, the fail ed battery emits hydrogen gas and the smallest spark can set off a catastrophic failure.   

Please be careful and monitor every battery on board your boat for temperature and voltage and keep your electric boat safe for you and your passengers.   

The technology exists to have a safe battery bank.   Pure Lead 12 volt  Batteries in series with monitoring.   Its really simple, and safe.    


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 Jun 6, 2017, at 7:40 AM, Jeff LaCoursiere jeff@jeff.net [electricboats] wrote:

 


That isn't correct - 12 x 6v in series would be 72v.  The OP was originally correct - 2 sets of 6 x 6v, the two sets in parallel.

I'll throw out a guess that you could then keep your original chargers, and use them in the same manner - just charge each 36v bank just like before.

j

On 06/06/2017 07:33 AM, Daniel Michaels nov32394@yahoo.com [electricboats] wrote:
 

They would all be in a series. One battery charger. Same as a golf cart.


 

I recently bought a 2002 Canadian electric boat Fantail Launch.  It has 36v system, with two groups of three 12v batteries in series, then the two groups linked in parallel.  There are two ProTournament series 3-step marine battery chargers, each dedicated to one of the 3-battery groups.

I fear the current six 12 v Interstate batteries are approaching end of life, and I'm interested in changing over to the 6v golf cart batteries with the higher amp hours capacity.

I need a 36 volt system for the current motor.  So, would I be linking 12 of the 6v batteries: two series of 6 in parallel?  Would I need two more charges to charge the added 6 batteries?

Thanks, and Regards.
M Kirkwood












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