Ya normally you sail with the props just off neutral, in a slight “on” position for Regen. I’m not sure if this is to overcome the “start” of the prop spin or what but it also reduces drag somewhat I believe. It’s one of the things that have always irked me when people talk about “drag” of the props. Speaking of drag I’ll also mention that it would seem that systems that are built around belts and pulleys would definitely increase the drag especially on smaller boats were the larger ones would have inertia in play (guessing on this).
The idea behind the Balancing System is to maximize the charge as much as possible. The BMS isn’t the charge source; it’s the ability to allow the charger in any stage to continue charging the bank until all the batteries are full. In bulk charge the charger is typically set to a limit and time duration. In my case 176v for 4 hours. If it get’s to either limit it goes to the next stage, 168v for 8 hours then 164v for 999hours at 5A trickle. So at all stages the balancers are moving the voltage around to equal them all however at all times there is some usage going on so they are constantly changing. The trick is to keep them as close to each other as possible. The HDM balancers have the ability to move up to 5A around, the highest I’ve seen so far and equal to the charger in maintenance mode. All of this is to be proved, I just got back the updated Balancer from HDM today and will install this weekend. We shall see….
Steve in Solomons MD
Lagoon 410 SE
From:
Sent: Monday, July 11, 2011 8:12 AM
To: ELECTRIC BOAT GROUP
Subject: Re: [Electric Boats] Re: Thoughts on regen and batteries
Steve
Now I see that unlike a charger the BMS never stop actually charging. Though it sounds like a little electro sailing turning the prop slightly might make sure your battery bank is never fully charged and give you additional boat speed also. Not a bad problem to have IMO.
Capt. Mike
Sent from on board BIANKA
http://biankablog.blogspot.com
From: Steve Dolan <sdolan@scannersllc.com>
Sender:
Date: Mon, 11 Jul 2011 06:11:12 -0400
To:
ReplyTo:
Subject: RE: [Electric Boats] Re: Thoughts on regen and batteries
Mike,
Under Regen or the Genset there’s nothing to say that the batteries are all full like your chargers. Even If everything is full it keeps on charging from the Regen under extreme conditions such as surfing down swells for extended periods. This is what happened on the first TransAtlantic when they had to run the A/C units and slightly in reverse. The Genset is set to a maximum voltage output so isn’t as big of a problem. As the batteries reach a full state the Amperage decreases at the genset. The Balancing system just insures that the battery pack is brought to as close to equal across the string as possible.
Does that make sense?
Steve in Solomons MD
Lagoon 410 SE
From:
Sent: Saturday, July 09, 2011 7:34 AM
To: ELECTRIC BOAT GROUP
Subject: Re: [Electric Boats] Re: Thoughts on regen and batteries
Steve
I am a little confused. I thought the reason to install a BMS (battery management system) was so that when one battery in the string is fully charged the BMS circuit stops charging it while the others continue charging until they too are charged. I can accomplish this using my Dual Pro charger which is essentially four separate chargers each one connected to a battery in my 48 volt string.. My question is why do you have to worry about over charging the bank when using regen or the generator when you have a BMS system installed? It seems to me the BMS does not know what the charging source is and should work regardless of the source or am I missing something?
Capt. Mike
Sent from on board BIANKA
http://biankablog.blogspot.com
From: Steve Dolan <sdolan@scannersllc.com>
Sender:
Date: Fri, 08 Jul 2011 12:35:20 -0400
To:
ReplyTo:
Subject: RE: [Electric Boats] Re: Thoughts on regen and batteries
Mark and Keith,
Thx Mark,
I thought the series charging problem was more a "rising tide floats all boats" - so the string gets up to full voltage only by over-charging the 3 good, but the charger cuts out before the bad one gets up to full voltage. But charge acceptance in the bulk phase is higher in the weak battery (right?)- so it perhaps does get more watts proportionally, but not before the (conventional) charger cuts out, leaving it at a lower voltage than it's peers (I have a weak understanding of all this at best...corrections appreciated)
That's what I'm hoping the Balancing does, Take a little power from the strong batteries and keep it going to the week one. So far that is what I've seen from the working HDM Balancers. My charger is on Maintenance Charge of around 5A max so any imbalance can be brought up across the string. At least in theory that's what I'm hoping it does without me doing anything other than looking at the PakTrakr. As Mike said the last 2 (in my case I have 2 PK modules since I have 12 batteries) are slightly lower than the rest so hopefully the HDM system will continue to pump the low batteries without overcharging the rest.
I also think I remember someone (Arby?) stating that the method of regen charging from brushless controllers is a high-voltage pulse - in which case there's no 'cutoff' voltage.
This is also correct, I have to monitor the battery state when regenerating or when running the genset to insure that the batteries aren't overcharging. It's not as critical with the genset because I can set the output level(in my case 164V) to what ever I need and the recharge (amps) of the batteries falls off as the voltage is met by the pack.
But...I didn't expect to get anything "free" out of this - just got me thinking that if we could use regen on the weak batteries, the effective increase in range might be "good enough" to justify some effort and expense in having it work. (but a discharge BMS provides the same benefit...)
I'm not sure how this could work (greater minds out there can say) since most charging is based on the highest battery charge condition, in other words if one battery gets to 13.6v then it goes to its next step down (I think!)
Maybe enough Leaf's will crash out of the fleet in the next year we don't need to worry about it :)
-K
--- In
>
> Keith,
>
> Unfortunately, charging a 48v series string of batteries undercharges the weakest one and overcharges the fullest one. Something about internal resistance being proportional to voltage, but in the wrong direction for naturally balancing batteries.
>
> This is true for lead-acid chemistry, but reportedly not true for some lithium chemistries. Lead acid cells naturally and slowly diverge over charge-discharge cycles. That is why flooded lead acid batteries are "equalized", or more accurately, severely overcharged, so that each internal cell of the battery is absolutely full, or equal in voltage to it's neighbor.
>
> AGM lead batteries should not be severely overcharged... it drives off the irreplaceable moisture. That is why AGM smart chargers are required for long-term AGM battery health.
>
> It would be marvelous to have a BatteryManagementSystem that took what little regen was available, and stuffed it into the weakest battery.
>
This is what I'm hoping the HDM Balancers will do!!!!
> Gonna sail
> Mark Stafford
>
>
> --- In
> >
> > Thinking about the case of a weak battery in a string (say 4x12)...
> >
> > In the above scenario (and there is _always_ 1 weak battery in a string...) - isn't any 48+V charging source selectively charging the weak battery (more charge acceptance)?
> >
> > Sailing around in good wind this weekend and getting 1-2amps regen pretty consistently according to my CycleAnalyst...it ain't much, but when I did have to motor up, it seemed that my voltage stayed higher, for longer, than this small about of charge would account for...which got me thinking....
> >
> > Since the weak battery ultimately determines the effective voltage of the string (and hence your range) - is it possible that just looking at overall watts in isn't telling the whole story? Can we capitalize on that (BMS system, etc)?
Keith, I've seen the same thing on regen it seems that the pack was happier and stayed higher longer. By the way I get about 1A at around 6 knots per motor (2 of them) which handles most of my needs until the frig. kicks in. :o)
Steve in Solomons MD
Lagoon 410 SE
No comments:
Post a Comment