Diodes:
Diodes will typically have a drop of .6 of a volt or so.
If you are running at 100 amps - multiply by .6 of a volt, and you have a 60 watt loss through the diode. So the diode had better be cooled. And this is a loss of energy that doesn't help with efficiency of the entire system.
But there are other problems with the diode approach. If the charger is in the system on the bus after the diode, it might not see the battery to be able to know the actual voltage of the battery pack. Some chargers and charge controllers will not start up if they don't see the battery. So the charger would have to operate directly on the battery and not be on the bus after the diode.
And if the charger is after the diode, it will be charging at 14.5 or so on the bus, but the battery will only see 13.9 volts and will never get fully recharged. This was a problem for battery isolators on 12 volt systems, so some chargers or charge controllers had voltage inputs from the batteries themselves so the charger could up the voltage to compensate for the voltage loss of the diode.
If the charger is connected directly to the battery, then it probably won't be going through the shunt, so you won't know your true battery capacity because the shunt relies on knowing the charging currents to set the monitor back to full battery.
So I would say the diodes are possible to use, but problematic, and unless you address all the problems properly, then the diode approach will be less than desirable and will never be as efficient as one good battery pack properly looked after.
It is usually the charger that ruins the batteries by taking the weakest battery over voltage and leaving all the rest at less than required voltages.
It all depends on the charging voltages experienced by the battery.
If a battery has a recommended charging voltage of 14.5 volts, and the batteries go out of balance by .1 or .2 volts, then during charge the 14.5 can become 14.7 and the battery can start to weaken by the over voltage condition and the remaining batteries weaken because they never get fully charged.
Always check the voltages during the end phase of the absorption charge, right before it goes to float. That is where you will see the most diverse voltages in the string. That is where the charger typically damages the string, over-charging one battery in the string, and under charging all the rest.
When one battery in a string becomes weaker than the other batteries in the string, it becomes smaller in amp hour capacity.
So lets say you have 200 amp hour batteries in a string and one weakens and it becomes 180 amp hours. That battery will fill up before all the other batteries, but the 48 Volt charger will keep on charging until the 48 volt charging parameters are met. So the 180 amp hour battery is now full, but energy is still pouring into it. The energy has nowhere to go except to start boiling off the electrolyte. On a flooded battery you can add water, but on a sealed battery you can't and you start doing damage to the battery pack.
48 volt chargers are inherently flawed when they are relying on the string for the information to terminate bulk or absorption charging. Each charge cycle, the string goes incrementally more out of balance until such time that the charger ruins the battery.
Batteries on average in a 48 volt string last 4 years or so. Add a battery management and you can get 10 to 15 years. I would say that is a good value, considering the price of replacement batteries, the labor to change them, and the reality that a failed battery can strand an electric boat.
Another nice thing about the Northstar Battery is the charging voltage can be anywhere between 14.1 volts and 14.7 volts. So if we choose 14.4 or so, we have leeway of .3 of a volt before we start damaging the battery from an overcharge condition.
To get a string to behave correctly it is really important that the batteries have the same life experience, which includes the same date of manufacture, the same warehousing, the same transportation, and the same charge discharge history.
I spend a bunch of money returning batteries before starting to buy them by the pallet. I age the batteries two or three months then observe their resting voltages and group them by their natural resting voltages.
Northstar batteries time and date stamp their batteries. Some suppliers will bring in batteries from different sources or different manufacturing dates and you would never know it. But stamped on a Northstar are the time and date stamps. The last batteries I shipped yesterday, were all made within minutes of each other, and were all within .01 of a volt of each other. Now those batteries will be very happy in a string.
You have to remember that no matter how good a battery is, it is guaranteed to fail over time. I know this is a harsh statement, and not what any purchase wants to hear, but it is true. What matters is if that failure will be graceful, or ugly, and if that failure will strand the vessel during operation.
I build two charging systems, one with separate chargers, and one with a 48 volt charger with balancer and monitor. The Balance and Monitor system we are currently working on can charge batteries at up to 3.2 KW while at the same time charing a house battery at 1.6 KW, making it a 4.8 KW charger. You need to work on the 48 volt bus to have a very high output charger like this, and when charging on the 48 volt bus you need to enable the charger based on not exceeding voltage or temperature set points of the individual batteries.
All of the chargers we use at Electroprop are completely programmable, so in 10 to 15 years when the batteries fail, the charger can be reprogrammed for any new technology at that time.
The other big flaw with most chargers is the way the absorption phase is terminated. Most chargers get to absorption voltages and terminate by keeping the voltage for a period of time. ( most usually 4 hours) This is the wrong way to terminate absorption charging.
The best way to terminate absorption charging is to wait until the charge rate decreases to 2 percent of the amp hour capacity of the battery. So a 200 amp hour battery should terminate absorption charging when the charge acceptance drops to 4 amps. And that should be measured by what is going into the battery and not what is going into the 48 volt bus which could be significantly different if their are loads on the bus.
If a battery terminates by time, and you unplug the battery charger then plug it in again, it may go back into a 4 hour absorption period. On high efficiency Pure Lead batteries, this can over charge the battery. But if you are terminating by current and you reset the charger, it will fall out of absorption in minutes rather than hours and the battery will be protected.
Symptoms of a Failed Battery:
1) Heat in the any Battery at any time.
2) Anomolies in the voltages. Load test the batteries. Note the voltage under the same load of say 40 amps or so over time. If the 48 volt battery starts off when brand new with a voltage of 50 volts under a 40 amp load, when the battery is failing you will see this voltage under load drop significantly…. Keep a log book and check periodically what the voltage of the bus is under the same amp load. Easy to do with any electric propulsion set up.
3) Voltages of the individual string varying by over .2 of a volt
4) Perhaps the best way is to keep an eye on the resting voltages. After the battery is fully charged, unplug the charger. Run the motor for a minute to get rid of the surface charge on the plates. Wait a couple of hours and observe the resting voltages. A healthy battery will have a resting voltage of 12.8 volts for a 12 volt battery. When the battery loses its capacity, the resting voltage will decrease. I estimate that when the resting voltage drops to 12.2 volts, the amp hour capacity of the battery, providing their is no other flaw, is about 1/2 of the original capacity of the battery. Once again, keep an eye on the resting voltage, and look for anomalies.
5) Remember a string of batteries in series is only as good as the weakest battery in the string. So look for the weak battery.
6) Voltage of the individual batteries exceeding manufacturers recommended setting during absorption charging, and most notable at the end of the absorption charging period.
If you use the one charger per battery solution, you can replace batteries one at a time. If you have a 48 volt charger you have to replace the entire string of batteries, when one of the batteries in the string fails.
Look after your batteries, and they will look after you!
James
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Jun 11, 2017, at 5:13 AM, Carter Quillen twowheelinguy@yahoo.com [electricboats] wrote:
Scott,One of your videos didn't play and the other one, to my surprise, was of me from over 5 years ago. And that's more than just a little ironic too because I have been following this thread carefully lately as I have a 5 year old, 48V pack of 6V batteries with several batteries that seem to be using a bit more water lately. They are also in parallel with another pack that I added about two years ago. I do have disconnect switches on each pack and a selector switch so I can operate them separately and run off either one or both. I normally leave them ganged together and this has worked great since I added the second pack and overall the system operates extremely better with the two packs working together. However I have found that they are charging and discharging at a slightly different rate now when I check the two circuits with a clamp on amp meter while running and charging. The 5 year old pack are Trojan T-125s and the newer pack are T-105s.I have two questions for James, or anyone else that wants to answer:When you parallel two 48V packs together, can you put a large diode coming from each pack to a common bus and solve the problem of one pack discharging to the other if one grounds out?Please elaborate more on symptoms to look for in a failing battery pack. What is considered out of balance, Is 0.1V to 0.2V difference between batteries enough to panic over?Capt. CarterOn Wednesday, June 7, 2017 9:30 PM, "James Lambden james@electroprop.com [electricboats]" <electricboats@yahoogroups.com> wrote:
Batteries in parallel get dangerous at the end of their life. So yes you can go out and have a good time for years, but then one day your batteries start gassing off hydrogen gas. They can gas off when charging or when discharging and yes they can blow up. It can be quite disconcerting to see your battery in pieces and acid all over the place. Might even wreck your mood that day.Be careful, and monitor batteries for balance more near the end of their battery life, and replace the entire pack when the voltage gets spongy. If there is any abnormal warmth in the battery at all, or any anomaly in the performance, its time for a new pack.this applies to all lead acid battery packs.Safety First Always. We don't want carelessness to ruin years of good fun with electric boating.James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.comOn Jun 7, 2017, at 11:11 AM, smasterson2@gmail.com [electricboats] wrote:Headed out boating today on this dangerous thing, just like I did dozens of times last year...
https://www.youtube.com/edit?o=U&video_id=BRqcp4Tzzrg
And tomorrow, I am headed out on this dangerous thing, just like I have for the last four years...
https://www.youtube.com/edit?o=U&video_id=JfkzrLlUhtg
Stay dangerous my friends.Scott Masterson
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Posted by: James Lambden <james@electroprop.com>
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