Don't get it: batteries

My inverter isn't working so can't charge batteries at the berth (or make air from the compressor or have AC aboard.) On minimal "life support," the boat uses about 1.5 percent of battery charge a day, so after two weeks, the batteries dropped from 98 to 75 percent. This last Saturday, went on a four-hour outing to recharge the battery, expecting a five-percent recharge per hour.

Well, after two hours, the battery charge moved from 75 to 85-percent charge. But then soon after, it bounced to 100 percent where it remained at that level for the remainder of the voyage.

Can anyone explain the bounce?

If your inverter is on the fritz maybe your %charge meter is too.

If its a Zantrex, they make a very satisfactory splash...

It's a Victron:

Guess I would start by checking the state of charge tomorrow to determine if the battery actually reached full charge or not. Battery age?

Ted

Batteries in the 80% plus range slow down a LOT in the recharge process. Specific batteries may be at a bit higher or lower % where they will accept less. From your description you were not far from that level.
Many SOC meters determine the recharged state by monitoring the amp hours put back but also the level of current flowing to the batteries. When the actual charge current gets to about one or two percent of the amp hour capacity of the bank/bank, based on what you have told it, for a specific time, again meter program, then it will figure the batteries are fully charged.


For all intents and purposes the batteries are at 100% even though the continuing very low current will add a bit of charge. The meter will ignore it as its requirements have been met.

The charge rate YOU see may not follow your expectations exactly.

Check the batteries after the NO LOAD/NO CHARGING waiting period and you likely will find they are right up.

The meters are a good guide but are not absolute.

I am no expert but I have noticed my battery monitor gives a state of charge that does not coincide with battery voltage. IOW battery voltage when compared to the battery voltage vs state of charge graph supplied by the battery manufacturer does not reflect what the battery monitor indicates. The monitor always indicates a state of charge much higher than the graph.

2 things to consider:
True battery voltage is indicated when the batteries have been unloaded and not charged for 12 hrs. The battery monitor cannot of course take this into account.

The battery monitor must be calibrated for the correct amp-hrs when fully charged. Once a battery is used and not new I have no idea how to figure it's amp-hr rating.
And to further confuse things a multi battery bank will most likely have batteries with different amp hrs even if they had the same amp hr rating when installed, especially if they have been used for a while.

So I don't really use state of charge to determine battery condition. I think amps used is a better indication.

At least this is how I understand it. I'm however probably wrong.

Take a voltage reading with the inverter on, should be above 13.2, 100% charged, and a voltage reading with the inverter off. It should tell you at least if the inverter is working. This is old school. If you want to know the true voltage, then you have to disconnect every from the battery. Poeple say you should wait, but I have found waiting does not change the reading much. 13.2 v=100%, 12.8=75%, 12.4=50%, l less than 12.2 battery need recharging.

Also you can have multi charging sources for DC as the cycle is flat.

13.2v is where most chargers will drop to to hold a batt at Float. .

12.8 is what most batt. mfg. consider a 100% charged batt.

Batt chargers "see" the batt as a voltage , and charges with the voltage differential it sees .

Charging with multiple chargers only is faster with a dead 10v batt where all the chargers see rotten voltage and charge as hard as they can.

To charge properly at least a volt over the resting state and usually more is applied.

An almost full 12.8 batt will be getting 13.8 to 14.4 as charge voltage.

When at the charge voltage, the charge should then go to float, 13.2 to save watering.

Any time there is a choice its better to charge batts from a single source only.

2 Alts? charge 2 sepirate banks , do not combine everything.for "fastest" charging.

It is NOT like pouring water in to fill a bucket , as in this case each hose has a variable valve (the voltage regulator) that controls its rate of fill by what V it sees..

Phil Fill said:

Take a voltage reading with the inverter on, should be above 13.2, 100% charged, and a voltage reading with the inverter off. It should tell you at least if the inverter is working. This is old school. If you want to know the true voltage, then you have to disconnect every from the battery. Poeple say you should wait, but I have found waiting does not change the reading much. 13.2 v=100%, 12.8=75%, 12.4=50%, l less than 12.2 battery need recharging.

Also you can have multi charging sources for DC as the cycle is flat.

Click to expand...

It may be old school, but I agree, you can't tell much by looking at the surface charge so you either have to wait (best) of take it off by turning the starter for 20-30 seconds, then read your rested SOC.

markpierce said:

My inverter isn't working so can't charge batteries at the berth (or make air from the compressor or have AC aboard.) On minimal "life support," the boat uses about 1.5 percent of battery charge a day, so after two weeks, the batteries dropped from 98 to 75 percent. This last Saturday, went on a four-hour outing to recharge the battery, expecting a five-percent recharge per hour.

Well, after two hours, the battery charge moved from 75 to 85-percent charge. But then soon after, it bounced to 100 percent where it remained at that level for the remainder of the voyage.

Can anyone explain the bounce?

Click to expand...

I take it you are getting your info from the Battery Monitor that works off the main Shunt ..... If so, this monitor is cabled via Cat5 data cable from the shunt, maybe there is an issue with this .. ? Myself, I would like to see the actual Amps going into the battery ( when / if, charging )

Victron is a good unit ! I have the 3000 multi now and also had one for a few yrs. on my sailboat.

There is a guy that is very respected in the marine electrical & battery issues here in Toronto, he is also a dealer for Victron. The guy is good !!! and I found him helpful. Paul Olsen........ Ontario Battery Services Co. Ltd.
sales@ontariobattery.com cheers .. Frank Bryant

Buy a DC clamp meter (<$50) and you can read the output of your charger/draw from the inverter. Caution when you go to buy one, many are AC only, make sure you get one that can do 400 amps DC. You won't normally get a reading that high but you have a buffer for the longer life of the meter.

This will tell you if your SOC meter has baked or if it's correct and your Victron has had it. I don't know if Vs can be repaired, if it was a Zantrex its not repairable as the (insert the boat word of your choice) will not give out the schematics. Ask me how I know?

C lectric gave the right answer in post #6 above. The behavior you experienced is entirely normal and is a result of the SOC meter's charge sensing algorithm.


David

Experienced the same before the inverter broke down. By the way, the boat has a 24-volt system, and the engine's alternator has a capacity of 150 amps, and the batteries are AGM.

markpierce said:

Experienced the same before the inverter broke down. By the way, the boat has a 24-volt system, and the engine's alternator has a capacity of 150 amps, and the batteries are AGM.

Click to expand...

It's all 24vdc? Must be inconvenient for electronics though good for heavy loads. I can't imagine trying to source everything in 24v - like my security cameras.

I have both 12v and 24v - the Volvo TMD100A needs 24v to start. When I bought it there was a whacky relay that series connected two 12v batteries to start.


Keith

markpierce said:

the batteries are AGM.

Click to expand...

Sounds similar to my two AGM bow thruster batteries before they died this past summer. Are you sure they are in good shape?

"I have both 12v and 24v - the Volvo TMD100A needs 24v to start. When I bought it there was a whacky relay that series connected two 12v batteries to start."

For 30+ years big trucks and buses have use equalizers to solve this hassle esp when 24v is the alt output..

How it works ,,, it loads one 12V batt for a few seconds then the other ,back and forth, so both are brought down the exact same amount .

The batts must be equal size and age for it to work.

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Since your inverter/charger has been on the fritz intermittently for the past several months, you may have experienced some battery degradation. But being AGMs, your batteries are more tolerant of poor charging than lead acids.

My LA house bank is on the SOC and as others have stated, sometimes indicates higher voltage than the %SOC would lead you to believe. The SOC is ball park, but not the final word on battery state. If I was you, before I did anything with the batteries, I'd repair/replace the faulty inverter/charger. Once that's done, you'll hopefully get more reliable charging, a full functioning vessel and a better look at your battery state.

If you buy a new one of the same model, I can help you replace the unit so you can have the current unit repaired as a spare. Free labor except for the IPAs when we're done and it's working.

FlyWright said:

...

If you buy a new one of the same model, I can help you replace the unit so you can have the current unit repaired as a spare. Free labor except for the IPAs when we're done and it's working.

Click to expand...

that offer would be hard to decline

refugio said:

It's all 24vdc? Must be inconvenient for electronics though good for heavy loads. I can't imagine trying to source everything in 24v - like my security cameras. ...

Click to expand...

While my power source is 24 volts, I've got 12-volt circuits too.

refugio said:

It's all 24vdc? Must be inconvenient for electronics though good for heavy loads. I can't imagine trying to source everything in 24v - like my security cameras.

I have both 12v and 24v - the Volvo TMD100A needs 24v to start. When I bought it there was a whacky relay that series connected two 12v batteries to start.


Keith

Click to expand...

Some electronics (Furuno) can accept voltage from 12-32 without any changes right out of the box. There are others.

markpierce said:

My inverter isn't working so can't charge batteries at the berth (or make air from the compressor or have AC aboard.) On minimal "life support," the boat uses about 1.5 percent of battery charge a day, so after two weeks, the batteries dropped from 98 to 75 percent. This last Saturday, went on a four-hour outing to recharge the battery, expecting a five-percent recharge per hour.

Well, after two hours, the battery charge moved from 75 to 85-percent charge. But then soon after, it bounced to 100 percent where it remained at that level for the remainder of the voyage.

Can anyone explain the bounce?

Click to expand...

Back again, 13 days after the above observation, the battery level was at 79 percent, about what was expected from starting at 100 percent. After 140 minutes of operation today, the charge had reached 90 percent and then an instant later the reading was a full charge of 100 percent. The voltmeter began at a reading of 28 volts and ended with 26 volts, which was normal.

What has changed in the past 13 days? Same inoperative inverter/charger? Is that what's providing you the charge data? If so, I wouldn't trust it until verified by an independent and fully functioning system.

Why not just buy a new unit?

No change. Been frustrated replacing it. Last year after taking the boat to the yard, the inverter began working again. Also, two companies haven't returned my calls. Meanwhile, operating the boat a couple of hours every couple of weeks or so, relying on the engine's alternator, keeps batteries adequately charged despite the jump in charge level readings.

Can anyone explain the bounce?

The V regulator only knows volts . I believe the unit charged to 85% , and then switched to float .

Perhaps an adjustment is required as batts only brought to 85% , see that as the "norm" and so shrink in terms of output available.

It takes mucho time above 85% to finally get to a full charge , so long many cruisers don't bother , or use solar for the final 10-15% .

This is well understood and the "shrinking" due to perpetual under charge is why many cruisers start out with oversized batt banks.

Well, looks like there is little to worry about over-charging the batteries.

So, given a 440 amp battery which can only readily be charged 85 percent and wanting to avoid discharging below 60 percent, there are only 110 amps available before recharging?