Sterling Battery to Battery Charger

[Richard10002]

There has been some discussion of using these in a variety of situations... the latest being to charge a battery in the bow.

http://www.sterling-power.com/products-battbatt.htm

How does it work?
The unit monitors the engine start battery, the unit will not start until the battery voltage exceeds 13 volts, then it waits for 2.5 minutes to ensure that some charger is replaced after engine start, it then pulls the engine battery down to no less than 13 volts, this enables the engine battery to still receive a charge and ensures the alternator works at its full potential to further ensure the engine battery is OK.

reading the above, it looks like it should only ever be connected to use the engine starter battery as the primary supply. If it were connected between the domestic batteries and the bow battery, it seems that it would stop charging the domestic batteries as soon as they reached 13v, and all the excess would go to charging the bow battery.

Presumably, as the engine battery only gets discharged a small amount, when starting the engine, thus doesnt need much charging, it's OK to leave it to charge at 13v.... but I dont think the same argument can apply to domestic batteries.

So a smart charging system for the domestic batteries, and a battery to battery charger for the bow battery seems to be the way to go, (alternatively, a battery to battery charger for each?)

Am I reading this correctly?

 

[Guest]

The correct sizing of the unit determines the share. If the Battery to battery charger, for the bow battery, is 40A max and the Alternator with regulator can provide 60 Amps into 13v then you get a reasonable share each.

Since your starter and house are close together then a simple VSR would be adequate.

I would have thought that it is absolutely essential that the BtoB is smaller than the Alternator and that alternator is directly to the starter battery. Otherwise, imagine a single output Alternator that went direct to house bank, when using small charging sources like solar (engine off) the VSR and BtoB would start having fights. Having the VSR sense only the starter battery would keep the starter battery out of the system unless the alternator was active.

 

[Anonymous]

Basically it's a dc-dc convertor. The circuitry is much the same as a mains invertor, but it gives dc out and not ac. It takes input voltages of between 13.0V and 14.8V and provides an output of up to 16V dc or even more, I suspect, whatever is needed so that at the end of a long cable the terminal voltage of a remote battery is at the correct voltage for the instantaneous state of charge. A sense wire monitors the remote voltage and is used to compensate for volt drop between the dc-dc converter and the remote battery.

It could have been designed to work from a much lower input voltage - e.g. 10V to 14.8V but they don't do that otherwise the device might discharge the main house (or start) batteries to charge the remote battery. That's why they chose 13V - if there is 13V present then the start or house battery is not being discharged.

It is a sensible idea since convertors are efficient these days.

BUT - they can produce horrible Radio Frequency Interference which might be very hard to suppress, and that will be the real test.

I put a similar thing on my bow battery last winter, but mine is a very small 12Ah battery to supply local electronics, so I have a small 100mA dc-dc convertor which I have modified to produce 14.5V exactly, which is ideal for the little sealed lead acid I am charging. Mine generates the higher voltage from the incoming power lead that can go down to 8V when the windlass or bowthruster are running. It works a treat.

 

[William_H]

A battery to battery charger is an interesting concept possible with modern switching converters. It is easy to control the voltage/current out to get the smart charging regime.
The advantage is that you can extract the maximum current out of an alternator for fast charge. This is because the alternator will only give its maximum current at a reduced voltage ie 60 amps at barely 12 or 13 volts.
An alternator is made to run a 12v system with battery charging as a minor function. ie made to run headlights heater ignition etc in a vehicle.
So in using a btob charger we want it to be able to charge well even though the input voltage is low fom the alternator but we don't wan t it to discharge the normal (engine) battery.

a manually switched sytem that disconnected the btob charger sometime before shutting the engine down would be ideal or at least a system that used say oil pressure to sense engine running so battery is not discharged with no charge. bearing in mind that voltage sensing is not so successful if you really want all an alternator can give.

Obviously getting into the regulator circuit of the laternator is the most efficient but not always an easy option.

So I wonder if I have got the use concept right and if anyone is using one and if they sell many. olewill

 

[Anonymous]

I think you might be right but I am not certain. Remember that the dc-dc converter simply transfers power at one voltage to power at another so what we are interested in is power output from the alternator, not Amps, per se. In other words, we are interested in the product Amps x Volts, not Amps. An alternator giving 13V at 40A is producing a power of 520 Watts and so is an alternator giving 12V at 43.33A. Without knowing more about the characteristics of the alternators out there, I couldn't be sure. However, I would have thought that they could set the limit to 12.6V since you are not going to seriously deplete a battery if you cap it at that.

Sensing engine running is not really an option as it presumes that a running engine must necessarily be causing the alternator to be providing charge. This would not be the case if the belt had broken, or if the alternator or its wiring had become defective. You still need a safeguard that your accessory batteries are not going to discharge your main batteries, required for engine start and nav.

 

[beneteau_305_553]

I have one of these and it works well.

The unit isolates the domestic battery from the engine starting battery and alternator. After the engine has been charging for 2 minutes the unit switches on the circuit to the domestic batteries. The output voltage from the alternator drops slightly due to the extra load. As the batteries become charged the load normally drops off the alternator but with this unit it increases the voltage to the domestic battery to say 14.4 V or what is best for your batteries to get them to full charge as quickly as possible. It does this by first inverting the dc to ac then transforming to higher voltage then rectifying to dc again.

This voltage then drops when the battery becomes charged to prevent overcharging.

Once the engine stops the domestic batteries are isolated from the engine battery to ensure engine starting battery is always fully charged. Its all automatic and eliminates getting the switches wrong and it does charge the batteries really well

The only complaint I have is electrical interference to the ssb radio. I spoke to the manufactureers and they said ssb should not be used on boats with one of these units!

 

[Anonymous]

[ QUOTE ]
The only complaint I have is electrical interference to the ssb radio. I spoke to the manufacturers and they said ssb should not be used on boats with one of these units!

[/ QUOTE ]Funnily enough I made that comment earlier - was it in this thread or the other one that is running in parallel with this? RFI is always a problem with inverters and converters but there is no reason why they should not have designed it to be quiet.

Clearly it has been designed and made by people who are not fit to supply goods into the marine market which has been my opinion of Sterling for years. They come up with some good ideas and on the surface the kit seems good but frankly it is not fit for use on a boat. Sad.

To state it clearly:-- If a piece of equipment sold for the marine market interferes with marine electronics such as the SSB then it is not fit for the purpose and should be returned to the manufacturer. There is no debate about it, in my opinion.

 

[pvb]

Best not to mince words...

[ QUOTE ]
Clearly it has been designed and made by people who are not fit to supply goods into the marine market which has been my opinion of Sterling for years. They come up with some good ideas and on the surface the kit seems good but frankly it is not fit for use on a boat. Sad.

[/ QUOTE ]Come on, tell us what you really think about Sterling! /forums/images/graemlins/shocked.gif

 

[nedmin]

The problem here is that we have been forced,because of the autumobile industry,to accept alternators,the dynamo was made defunct because it was more expensive.With modern materials and electronics I am sure it would be better for marine use, to go back to the dynamo.By the time we have added diode splitters, advanced regulators,ac to dc converters etc they are damned expensive alternators.I know that one of the reasons alternators took over is that at low revs the output is better but a dynamo could be made that would give equiv.output at low revs. but it would cost more,but not as expensive as all these peripherals we are adding on.

 

[Anonymous]

Re: Best not to mince words...

[/ QUOTE ]Come on, tell us what you really think about Sterling! /forums/images/graemlins/shocked.gif

[/ QUOTE ]They'd delete the post /forums/images/graemlins/wink.gif

 

[William_H]

Hi Nedmin I think you have rather a rose coloured glasses view of Dynamos. An alternaor with rectifiers ie what we call an alternaor for a vehicle is in my opinion the same as a dynamo only with improvements for longer life.

Both have a field coil to provide magnetism to generate power. The Dynamo has it on the outside the alternator on the inside. Both need a regulator to control the field current and so output of the generator.
The Dynamo has the rotor as the power generating coil and this must be rectified by the switching action of the brushes on the comutator. While the alternator has the outer coils as the power collecting windings and the AC is rectified by diodes.

Now the diodes of an alternator waste power inheat at about 1.5 volts multiplied by the output current Typically 30 watts at 20 amps.

The dynamo by comparison may or may not waste power in arcing at the comutator but will definitely have a limited life of brushes and comutator as all the current is carried through the brushes.

The brushes on the alternator carry only the field current 1 or 2 amps and make a connection on a smooth ring so very little arcing.

Because of the limitations dynamos were made for a more limited speed range. The heavier windings could fly apart at high speeds so in practice dynamos were not driven at high speed (pulley ratio) so tended not to charge at low speeds.
The alternator rotor having smaller wire in one simple coil shape aligned to the shaft can cope with much higher rotation speeds hence tends to charge at a lower engine speed.

So give me a modern alternator any time. olewill

 

[Chris_Robb]

[ QUOTE ]
BUT - they can produce horrible Radio Frequency Interference which might be very hard to suppress, and that will be the real test.


[/ QUOTE ]

No interfrenece noticed, despite being installed along side both the VHF and radion CD player. Not got an SSB so could not comment...

 

[Anonymous]

[ QUOTE ]
No interfrenece noticed, despite being installed along side both the VHF and radion CD player. Not got an SSB so could not comment...

[/ QUOTE ]Unfortunately we have two threads running at the same time discussing this Sterling product! I am not surprised that they have suppressed the device at VHF but a poster told us that he had problems with his SSB, and that Sterling told him that their battery to battery controller is not suitable for use with boats having SSB. Which is understandable as it is more difficult to do. I'd bet that it interferes with Navtex badly, as well, as well as RTTY and other weather receivers. Basically not suitable for use in a sea-going vessel, probably OK for the inland waterways. It isn't acceptable to run noisy equipment on your own vessel if you will be in the vicinity of other vessels....you have a duty and legal requirement to suppress your kit.

 

[jb267]

I have one of these on my boat. Fantastic piece of kit. Engine and domestic batteries always charged quickly. Electrics switched on at the start of my Summer cruise this year and only switched off 3 1/2 months later - no switching to worry about!

No interference anywhere on electronics including VHF and Navtex. (I don't have SSB though).

Compared to fitting alternator regulator, split charging systems etc, to me its a no brainer. I guess it depends where you are starting from though when upgrading your electrics.

 

[Anonymous]

I'm glad it's working well - as I said earlier in one of these two threads on this product, it is an excellent concept. The fact that you haven't (yet) had a problem with Navtex does not mean that you never will since Navtex only transmits for a short 10min period twice a day and if your charger has not been called on to do much it might not have been radiating. Navtex is notoriously prone to local interference in marinas, and alongside other boats. As for VHF, I would expect any problem to be on transmit, not receive, and it might not affect your intelligibility when the signal is strong. If you ever needed to transmit a distress call, it would be a good idea to switch it off (along with any fridges, freezers, heaters, mains chargers, and other noise-generating equipment).