Charge batts + supply DC?

[concentrik]

I'm about to lash out on a battery charger but before I do there's something puzzling me.

I'll have about 300aH of house batteries which I hope to charge every 2 or 3 days from shorepower. Away from marinas I'll be topping up with wind/solar (9A @ 15kn and 160W respectively) but I know I can't rely on that and I'd want to be sure of leaving shore with batteries fully charged overnight.

Apart from a fan heater and water heater which are 240v, all onboard systems are 12v. So when alongside I'll be using about 120W (TV, laptop, music - not all at once- and lighting etc) from 12v circuits.

At last, the question: some chargers claim to provide charge current and act as a DC power supply. How do they determine the charge state of the battery if there is an additional variable resistive load in parallel? How do they know what proportion of the supply current is flowing through the battery?

I wonder if there is a case for switching the battery bank out of the boat circuit when charging, connecting batts to a charger on their own, and switching in a (say) 30A switchmode psu to supply the boat? Perhaps this is normal practice anyway....

 

[noelex]

Most chargers work on battery voltage and time, Load current will have little effect on regulation. So you do not need to worry.
Some expensive chargers use shunts to determine net battery current these are also fine, in fact better.
A small number use charger current to determine regulation. These will be fooled by load currents and are not very satisfactory.

 

[halcyon]

At last, the question: some chargers claim to provide charge current and act as a DC power supply. How do they determine the charge state of the battery if there is an additional variable resistive load in parallel? How do they know what proportion of the supply current is flowing through the battery?.

The charger goes thought it's charge cycle, then drops to float charge, in this state it acts as a DC power supply. The answer to the second part is few concider service load, they act just as a battery charger.

Brian

 

[Stu Jackson]

What you need to consider is that 99% of battery chargers are basically dumb. Thy have NO idea what you're doing at the other end with your DC power use. I agree with the answer about float. If you want more juice, you simply have to turn the charger off once, turn it back on, and it'll go through its timed bulk, absorbtion, and float cycle all over again. Most of them work ona timed cycle for the bulk phase.

 

[Bosun Higgs]

How do they determine the charge state of the battery if there is an additional variable resistive load in parallel? How do they know what proportion of the supply current is flowing through the battery?

They dont. They try to supply an output voltage determined by their design but the actual voltage is limited by the current draw. Thus the battery charger might be trying to put out say 14.4v in its initial stage but if the current drawn by all the circuits hits the chargers max current before the voltage rises to 14.4 then the voltage stops there.

However some battery chargers have two or three independant output circuits so you could route one to the domestic batteries and one to the engine starter battery

I wonder if there is a case for switching the battery bank out of the boat circuit when charging, connecting batts to a charger on their own, and switching in a (say) 30A switchmode psu to supply the boat? Perhaps this is normal practice anyway....

You could do this. Better to buy one big battery charger. But have a chat with Sterling power. They make battery chargers and are very helpful with sensible advice including telling me last time that it wasnt necessary to buy one of their products as I had planned to do.

 

[mitiempo]

They dont. They try to supply an output voltage determined by their design but the actual voltage is limited by the current draw. Thus the battery charger might be trying to put out say 14.4v in its initial stage but if the current drawn by all the circuits hits the chargers max current before the voltage rises to 14.4 then the voltage stops there.

However some battery chargers have two or three independant output circuits so you could route one to the domestic batteries and one to the engine starter battery



You could do this. Better to buy one big battery charger. But have a chat with Sterling power. They make battery chargers and are very helpful with sensible advice including telling me last time that it wasnt necessary to buy one of their products as I had planned to do.

Battery chargers are voltage driven. In the different stages of charging - bulk, absorption, and float - they have set voltages. In bulk stage they will output up to their rated current as long as the battery will accept it. The battery determines the current. You can't put more current into a battery than it will accept for a given voltage. The only way to increase the current into the battery is to increase the voltage as Sterling does. But then battery maintenance increases.

 

[pappaecho]

if you are really going to top up the batteries every 2-3 days on shore power, you risk cooking the batteries, unless you have an expensive charger which will respond exactly to the state of charge of each battery. Frankly I would not recharge the batteries more frequently than every couple of weeks unless it is being discharged during the period

 

[ianj99]

I'm about to lash out on a battery charger but before I do there's something puzzling me.

I'll have about 300aH of house batteries which I hope to charge every 2 or 3 days from shorepower. Away from marinas I'll be topping up with wind/solar (9A @ 15kn and 160W respectively) but I know I can't rely on that and I'd want to be sure of leaving shore with batteries fully charged overnight.

Apart from a fan heater and water heater which are 240v, all onboard systems are 12v. So when alongside I'll be using about 120W (TV, laptop, music - not all at once- and lighting etc) from 12v circuits.

At last, the question: some chargers claim to provide charge current and act as a DC power supply. How do they determine the charge state of the battery if there is an additional variable resistive load in parallel? How do they know what proportion of the supply current is flowing through the battery?

I wonder if there is a case for switching the battery bank out of the boat circuit when charging, connecting batts to a charger on their own, and switching in a (say) 30A switchmode psu to supply the boat? Perhaps this is normal practice anyway....

I've been using a Sterling Prodigital 3 output 30amp charger which also acts as a power supply for over 2years and it is 'fit and forget' - it just does what it supposed to.
The power supply mode functions in an obvious way - once the batteries are fully charged, then the charger acts as a power supply, by maintaining the output at the float voltage.
It wasn't cheap (over £250 I think) but as I said, its fit & forget, and both batteries are always fully charged.

 

[BabaYaga]

some chargers claim to provide charge current and act as a DC power supply.

Some chargers have a "supply mode" which means they can be used as a 12 V power source without any batteries present. This is true of some CTEK models.
Could it be that you have misinterpreted the claim?

 

[Porthandbuoy]

I have a 16A Ring charger. Works fine, BUT, when the battery is fully charged and the voltage drops back to float, 13.6V (iirc) and I then turn on the Eber I get a battery fault warning on the charger. I'm assuming the charger 'sees' the sudden voltage drop when the load comes on as a bad battery. Smaller loads, such as VHF or lighting, don't cause any problems.
As a previous poster said, switching the charger Off then On solves the problem. The charger supplies the bulk of its amps to the Eber and just trickle charges the battery. As soon as the Eber is switched off the volts go up to 14.4 and the charger switches back to float.

 

[William_H]

Battery charging

I am a bit sceptical about the smart chargers that sense the battery state then charge at a higher voltage to get them charged quicker. Yes I understand the way a regulated voltage charger will have less charge current as batteries charge up so that full charge is hard to get.
I can see the OPs concern regarding current use during charging confusing the voltage sensing algorythms of the charger.
I wonder if OP has considered the possible problems of excessively high voltage on the 12v supply line.
Most equipment light bulbs etc are made for 13.75 volts supply. ie a typical battery n charge from an alternator regulator.
I think if it were my boat in the op case I would go for a regulated 13.75v power supply which will charge batteries and supply the load as necessary. Sure full and rapid recharge will be harder to achieve but all your equipment will be safe and batteries will stay fairly well charged. good luck olewill

 

[Porthandbuoy]

Most equipment light bulbs etc are made for 13.75 volts supply. ie a typical battery n charge from an alternator regulator.

I think you might be wrong there. My Yanmar 1GM10 bog standard, stock, off the shelf 35 Amp alternator regulates at 14.4 Volts. That's according to the manual and a high quality Fluke Multimeter.

 

[mitiempo]

I live in a marina full of liveaboards and all our chargers are on all the time. If the batteries are charged and on float and a load of any size it turned on the charger increases voltage and goes into absorption or bulk mode. When the load it turned off the charger goes back into float. There are no problems with light bulbs or anything else at the higher voltage - about 14.4 for flooded batteries - when the charger ramps up to replace the draw on the batteries. The alternator should be at about the same voltage when running the engine - all the time with a dumb reg and in bulk with a 3 stage reg. With a 3% voltage drop on the light wiring they see just under 14 volts when the charger is at 14.4. If wired for a 10% voltage drop as lights often are they see under 13 volts.

Full charge isn't hard to get - it just takes a while as the resistance increases in the batteries.

If you use the boat weekends or less often many chargers offer the option of 2 stage charging as well as the normal 3 stage charging. In 2 stage the charger sleeps after the batteries are charged and doesn't come on until the batteries reach about 12.5 volts. Xantrex chargers have this option and it is better for unused batteries not to be on a constant float charge. In the case of the Xantrex charger every 21 days the charger comes on to refresh the batteries.

 

[philip_stevens]

I've been using a Sterling Prodigital 3 output 30amp charger which also acts as a power supply for over 2years and it is 'fit and forget' - it just does what it supposed to.
The power supply mode functions in an obvious way - once the batteries are fully charged, then the charger acts as a power supply, by maintaining the output at the float voltage.
It wasn't cheap (over £250 I think) but as I said, its fit & forget, and both batteries are always fully charged.

Same model here, with no problems. Keeps the cool box, lights, TV, etc., going without depleting the batteries when in use.

 

[concentrik]

thread revival, last question...

I read the replies to the original post carefully - thank you to those who responded. I did as much research as I could but even then I didn't find a clear answer. I may be missing something, I know, but I couldn't find an explanation of how any charger could operate independent of parallel load without disconnecting that load to assess the true state of the battery bank.

So I expect I'll fit a cam-type changeover switch which will be turned when the boat is connected to shorepower. Yes it's an additional thing to remember but I could put a note on the shorepower plug to remind me!

The switch will connect the service load (boat) to a 50A switchmode psu and connect the battery bank to the charger (only the charger).I have a Black and Decker 30A 'intelligent' (ha!) charger for this.

Finally the question: should the engine alternator be disconnected during charging as the charge voltage appears to rise to about 15.6v?

 

[ianj99]

I read the replies to the original post carefully - thank you to those who responded. I did as much research as I could but even then I didn't find a clear answer. I may be missing something, I know, but I couldn't find an explanation of how any charger could operate independent of parallel load without disconnecting that load to assess the true state of the battery bank.

So I expect I'll fit a cam-type changeover switch which will be turned when the boat is connected to shorepower. Yes it's an additional thing to remember but I could put a note on the shorepower plug to remind me!

The switch will connect the service load (boat) to a 50A switchmode psu and connect the battery bank to the charger (only the charger).I have a Black and Decker 30A 'intelligent' (ha!) charger for this.

Finally the question: should the engine alternator be disconnected during charging as the charge voltage appears to rise to about 15.6v?

There is no point in such complexity especially when Charles Sterling has done all the hard work and research and built it into his products..

I have been using a Sterling Prodigital 30a charger for ovr 2years with no problems at all.
It switches into 'power pack' mode when the float voltage has been reached.

http://www.sterling-power.com/products-chargers-prodigital-techinfo.htm

You just fit an forget - its does what is claimed in the specs.

Here's an extract from the instructions: ...
Step 3 .. FLOAT/POWER PACK MODE....the voltage is held at 13.6v to maintain the charge without overheating the batteries... FULL CURRENT is available for onboard supply.

What else do you want?

Ian

 

[concentrik]

Ian - 30A is only 360W for the service load even if the batteries are fully charged when shorepower is applied - take off a modest 8A for the battery bank which is not fully charged and you're left with 22A. With the fridge/TV/lights/laptop etc etc I think I need more than the Sterling unit you mention can deliver - a 50A independent supply would provide this with capacity to spare. I wouldn't have to be concerned about 12V capacity if I wanted to add any other items as time goes on.

In the new year I'll call Sterling to ask them how their equipment distinguishes between a deeply discharged battery with no parallel load and a slightly discharged battery with a 20A p. load. I am expecting a robust response - if anyone else can explain this in the meantime it would save me thus exposing myself!

I'm guessing the alternator can stay connected.

 

[ianj99]

Ian - 30A is only 360W for the service load even if the batteries are fully charged when shorepower is applied - take off a modest 8A for the battery bank which is not fully charged and you're left with 22A. With the fridge/TV/lights/laptop etc etc I think I need more than the Sterling unit you mention can deliver - a 50A independent supply would provide this with capacity to spare. I wouldn't have to be concerned about 12V capacity if I wanted to add any other items as time goes on.

In the new year I'll call Sterling to ask them how their equipment distinguishes between a deeply discharged battery with no parallel load and a slightly discharged battery with a 20A p. load. I am expecting a robust response - if anyone else can explain this in the meantime it would save me thus exposing myself!

I'm guessing the alternator can stay connected.

Sterling also do 40 and 50amp Prodigital chargers.

There is no need to distiguish between the type of load, whether it be for a discharged battery bank or for ship's supply. The charger will supply however much current is required upto its limit (& allowable battery temperature).

It doesn't even matter too much if the total demand exceeds the charger's capability when for example the fridge switches on. The batteries will make up the shortfall and then will be recharged when the fridge switches it off. So unless you have a constant demand and only a short time to recahrge the batteries, I don't see where the problem lies. Just fit the appropriate sized charger.

The charger has a timer, whereby it switches off and monitors the drop in battery volts, clearly if this happens quickly, as it would with a high load and / or discharged batteries, it switches on again in absoprtion mode.
If the batteries are fully charged and there is no other load, clearly, the voltage will reflect the battery state so the charger switches to float / power pack mode - ie constant voltage. It then activates its timer regularly to check the actual battery voltage and switches to absorption mode if necessary to recharge the batteries before returning to float/power pack mode.

No, the alternator is not affected as it isn't whatever charging method is employed.

With the benefit of hind sight and a bigger budget, I would have fitted one of Sterling's invertor chargers.

http://www.sterling-power.com/products-icc-specs.htm

 

[mitiempo]

I agree with Ian.

Everything can stay connected. The batteries control any acceptance and when fully charged the charger will be in float mode. When a load is switched on the charger will go into absorption to supply what you are taking from the battery. I install chargers on a regular basis and live in a marina that is full of liveaboards. Everybody including myself just leaves the charger on 24/7 and it does its job as it should. Tha alternator has no issues. Even if you start the engine while on shorepower with the charger on there is not a problem. The shorepower charger or the alt would idle while the other charges, determined by the battery.

 

[ianj99]

I agree with Ian.

Everything can stay connected. The batteries control any acceptance and when fully charged the charger will be in float mode. When a load is switched on the charger will go into absorption to supply what you are taking from the battery. I install chargers on a regular basis and live in a marina that is full of liveaboards. Everybody including myself just leaves the charger on 24/7 and it does its job as it should. Tha alternator has no issues. Even if you start the engine while on shorepower with the charger on there is not a problem. The shorepower charger or the alt would idle while the other charges, determined by the battery.[/QUOTE]

Yes. I also have a Sterling digital alternator regulator and there is no conflict between it and the charger when the engine is running with shore power connected even though both batteries are connected in parallel by the alternator split charge relay.