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matthias-nagel asked

Recommended options for yacht wiring with two lead-acid batteries

Current situation:

The yacht has two 12V lead-acid batteries with different chemical and electrical characteristics: one starter battery with can provide a high curren but has a low capacity and a service/"house" battery with high capacity which allows deep cycles. The system are completely independent. The starter battery is only connected to the engine and exclusively charged by the alternator. The alternator is an old-fashion, regular alternator which constantly provides 14V. The service battery powers the cabin and navigation lights as well as the radio. A PV panel with 54V system voltage and an old PWM solar charger. Currently, there is no option to charge any of the batteries from on-shore power.

The setup shall be upgraded. Both batteries shall be charged by the PV panel but kept separate otherwise as they are different in chemistry and purpose. An option for on-share charging shall be added. The PWM charger shall be replaced by a MPPT charger.

If possible, I would like to keep the batteries and the PV panel in a first step and maybe replace the batteries in the future after they are will be worn down.

I have several questions:

  1. In order to charge both batteries, I need a DC-DC charger such as the Orion-Tr Smart DC-DC Charger. The manual suggests that the charging direction should be from the starter battery to the service battery. Why? Intuitively, I assumed that it would be more efficient to connect all chargers (on-shore AC charger, MPPT solar charger) to the service battery and the charge the starter battery from there. Most DC loadS which constantly draw power are connected to the service battery, while power is drawn from the starter battery only during engine startup. Hence, I guessed that it was beneficial to have power input on the service side, too.
  2. In theory, I could also connect the alternator to the service battery. Recommended?
  3. The alternator does not consider the SoC of the battery, but constantly provides 14V. Is it advisable to put another DC-DC charger between the alternator and the battery such that the battery is charged more "gently"? Or is the superfluous luxury?
  4. I found the Smart BMS which in theory seem to provide which I intend to achieve with the extra DC-DC charger. However, the manual explicitly states that the Smart BMS are designed for the VE LiPo batteries. Are the Smart BMS also compatible with lead-acid batteries as house batteries?
  5. How do several, different chargers interfere with each other, when they are connected to the same battery and all intend to charge the battery at once, i.e. the MPPT solar charger, the AC on-shore charger and the alternator (possibly decoupled via a DC-DC charger)? Are the "intellegent" enough to avoid any negative side effects?

Bests, Matthias

alternatorlead-aciddc-dc chargeryacht
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matthias-nagel avatar image matthias-nagel commented ·

The fourth question of my original post still remains unanswered:

I found the Smart BMS which in theory seem to provide which I intend to achieve with the extra DC-DC charger. However, the manual explicitly states that the Smart BMS are designed for the VE LiPo batteries. Are the Smart BMS also compatible with lead-acid batteries as house batteries?
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Kevin Windrem avatar image Kevin Windrem matthias-nagel commented ·
No. The Victron BMS devices connect to circuitry inside their LFP batteries via a proprietary interface. Lead-acid batteries have no such circuitry or connection.
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Kevin Windrem avatar image
Kevin Windrem answered ·

The input of Orion DC-DC chargers must be connected to a battery. Connection to an alternator without a battery at that same point will cause issues since the alternator does not put out a pure DC waveform.

Connecting the alternator to the house battery means you would have no way to control charging as the battery approaches 100% SOC. This might be OK for lead-acid batteries but not with LFP batteries. The internal resistance of LA batteries limits charging current to safe values. With LFP the resistance is much less so you can easily draw more from the alternator than it can supply. Damage to the alternator could result, especially at low RPMs when alternator cooling is minimal.

I would connect AC and solar charging to the house battery with a DC-DC charger from the starter to the house battery for charging via the alternator.

The alternator may provide sufficient charging for the starter battery in which case it may not be necessary to charge the starter battery from the house battery. A SECOND DC-DC charger from house battery to starter battery would provide emergency charging for the starter battery.

A simpler arrangement would be to connect all charging sources to the starter battery then have a DC-DC charger to charge the house battery from the starter battery. This charger might need to be fairly large to keep up with the loads on the house battery. While simpler, it is not as efficient as other designs.

If you do employ DC-DC chargers in both directions, you need to insure that they both don't operate at the same time.

Bidirectional DC-DC chargers are available but not from Victron.

Chargers connected to the same battery will sum their charging current. Care must be taken to limit the maximum charging current to the specs for your battery bank. In the Victron world, a GX device (Cerbo GX, Eranko GX, etc) can manage all charging sources to insure the battery does not receive too much charging current. But the GX device is really intended for systems with a Victron inverter/charger. You did not mention any AC loads in your system so a GX device might be an expensive addition for this limited functionality. The only other option is to size your battery bank and charging sources to avoid exceeding maximum current.

If you do have AC loads, consider a Victron inverter/charger. This may eliminate the need for a separate shore power charger. HOWEVER, Victron's AC chargers will typically operate on 120 and 230 volt power and their inverters are limited to 120 or 230 volt power.

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matthias-nagel avatar image
matthias-nagel answered ·
Connecting the alternator to the house battery means you would have no way to control charging as the battery approaches 100% SOC. This might be OK for lead-acid batteries but not with LFP batteries.

That‘s why I considered to put another DC-DC charger between the alternator and the battery. But as you wrote before the Orion DC-DC charger can not handle non-pure DC input.

Connecting an alternator to a lead-acid battery directly has to be OK (not only might be), because this is done currently and this what you suggest, too.

The input of Orion DC-DC chargers must be connected to a battery. Connection to an alternator without a battery at that same point will cause issues since the alternator does not put out a pure DC waveform.

While the alternator may be a perfect DC source, it still includes a rectifier and voltage regulator to keep the voltage around 14V. (Otherwise it would never charge a lead-acid battery in the first place.) The input range of the Orion DC-DC charger is something between 8V and 60V. (I was to lazy to look up the exact numbers right now.) So in principle, the Orion DC-DC charger can handle varying input voltage. Do you know how much "ripple" the charger can handle?

Chargers connected to the same battery will sum their charging current.

How that? I do not understand the physical/electrical principle behind that phenomenon. Could you explain?

I assumed that the charging current would be the result of the applied charging voltage and the internal resistance of the battery. I feared that multiple, parallel chargers would mutually influence their respective voltage measurement in a negative manner and thus causing an erratic control loop. Or that several charger try to work "against" each other and until the weaker one is destroyed. But I would never have imagined that the charging currents sum up.

Does this also happen, if I use a Smart Shunt which is paired with all chargers? Would this be an cheaper option then the Cerbo GX?

You did not mention any AC loads in your system.

Correct, I do not plan with any AC loads.


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Kevin Windrem avatar image Kevin Windrem commented ·

Battery chargers function as a constant current source during the bulk phase, then switching to a voltage source (which is still limited to the charging current used for bulk) for absorption and float. So the currents from all chargers in bulk phase will add together and feed the battery.

For chargers in parallel, the one with the highest absorption voltage will predominate. Same for float. But all charging sources should be set with the same absorption and float voltages so they switch modes at approximately the same time.

Paralleled charging sources are quite common. Consider a typical system that has one or more solar chargers, an inverter/charger, a wind generator, etc. All chargers combine to provide the battery with a total charging current.

A battery monitor (or Victron SmartShunt) by itself will not manage charging currents. Victron does provide a networking mechanism to tie multiple chargers together but this mechanism does not insure maximum charging current is not exceeded. It only keeps all chargers at the same charging phase.

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kevgermany avatar image
kevgermany answered ·

Some points/clarification. In addition to @Kevin Windrem excellent previous answer.

The alternator/starter battery setup is dumb, constant voltage. Ok for starter batteries, but house batteries are different and need a three stage charge cycle. As stated the starter battery smooths out the alternator supply. So connecting the Orion direct to the alternator when there's also a direct connection between alternator and starter battery is electrically the same as connecting to the starter battery.

Sum charging current - if you have two 30A DC:DC chargers in parallel, you have the sum of 30A+30A=60A as a charging current. This, with other loads from engine powered systems, may overload your alternator and destroy it.

For what you're describing, I'd put all the extra (i.e. none alternator) charging to the house batteries. As you are thinking I'd add an Orion to charge house from starter/alternator. You can consider an extra Orion to charge the starter battery. I found that a simple battery trickle charger such as the Votronic unit is perfectly adequate and much cheaper.

Make sure all the new additions can be configured for lithium or lead chemistries to minimise expense when you go lithium. The Votronic is not, but for it's price....


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matthias-nagel avatar image matthias-nagel commented ·

@Kevin Windrem wrote:

Battery chargers function as a constant current source during the bulk phase […]. So the currents from all chargers in bulk phase will add together and feed the battery.

[…]

A battery monitor (or Victron SmartShunt) by itself will not manage charging currents. Victron does provide a networking mechanism to tie multiple chargers together but this mechanism does not ensure maximum charging current is not exceeded. It only keeps all chargers at the same charging phase.

OK, so the source of the problem is that each charger attempts to maintain its "locally observed" charging current during the bulk phase, adjusts the voltage accordingly to meet the targeted current and hence the charging currents sum up.

You say, Victron networking mechanism does not ensure that the maximum charging current is not exceeded. However, if I understand the manual of the MPPT 100/30 correctly, there is a setting to limit the maximum charging current. Moreover, the MPPT 100/30 can be connected to a BMV-712 Smart via VE.Network over Bluetooth in which case the MPPT 100/30 would not use the "locally measured" current for control, but the actual current which is reported by the BMV-712 Smart. Shouldn't this suffice? Where am I erring?

Moreover, if I understand the purpose of the Cerbo GX correctly, the Cerbo GX should also control the maximum charing current, if a BMV-712 Smart is connected and DVCC is enabled. Shouldn't it?

The only problematic module seems to be the Orion Tr Smart DC-DC which despite having "Smart" in the name, does neither support a VE.Direct port for connection to the Cerbo GX nor support VE.Network and does not interoperate with any of the BMV. Right?

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Kevin Windrem avatar image Kevin Windrem matthias-nagel commented ·
Smart Networking will provide the charges with voltage, temperature (and maybe current), but that does not matter since each charger does not know about the others so the total current can't be determined and throttled back if necessary. This is true even if a battery monitor is present and could report total battery current.


Yes, Cerbo with DVCC enabled WILL insure the maximum charging current is not exceeded but sending each charger it manages a maximum current. It is true that the Orion does not participate in DVCC however, if it is suppling charging current, that will be reflected in the battery monitor and other (controllable) charging sources will be throttled accordingly.

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matthias-nagel avatar image matthias-nagel Kevin Windrem commented ·

Smart Networking will provide the charges with voltage, temperature (and maybe current), [...]. This is true even if a battery monitor is present and could report total battery current.

Why so? The shunt of the BMV-712 Smart measures the combined current of all chargers and loads flowing in/out of the battery. If I correctöy understand the manual of the SmartSolar MPPT 100/30 & 100/50, the MPPT uses the current reported by the BMV-712, see sec. 5.5, third bullet point after The VE.Smart Networking can be used for:

Current sensing - The measured battery current is used by the charger [...] To measure the charge current all charge currents from all chargers are combined, or if a battery monitor is part of the network the actual battery current will be used.

Same holds for the Phoenix Smart Charger. Only the Orion DC-DC Charger does not seem to be "Smart" despite it name.

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kevgermany avatar image kevgermany ♦♦ matthias-nagel commented ·

MPPTs follow internal settings, unless connected to a GX device. The GX device will adjust output of all chargers except Orions if DVCC is enabled.


With a BMV in the system, the current measured by it will be used. So if necessary MPPT output will be reduced to take into account any current from the Orion. Unless you install Orion(s) that can output more than the battery can take, nothing to worry about.

Smart/Bluetooth networking is intended for small systems and is subject to some limitations. Worth reading the paper. https://www.victronenergy.com/upload/documents/Technical-Information-Data-communication-with-Victron-Energy-products_EN.pdf


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matthias-nagel avatar image matthias-nagel kevgermany ♦♦ commented ·

Worth reading the paper. https://www.victronenergy.com/upload/documents/Technical-Information-Data-communication-with-Victron-Energy-products_EN.pdf

Why? The paper seems only to desribe the physical and link layer of the various types of interfaces and which product support which interface. I don't understand how that is supposed to contribute to the question.

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matthias-nagel avatar image matthias-nagel commented ·

@kevgermay wrote:

The alternator/starter battery setup is dumb, constant voltage. [...] As stated the starter battery smooths out the alternator supply. So connecting the Orion direct to the alternator when there's also a direct connection between alternator and starter battery is electrically the same as connecting to the starter battery.

That doesn't answer the question, but only repeats what has already been said. I specifically asked how much ripple voltage the Orion DC-DC Charger allows. A typical rectifier and regulator for a traditional alternator provides between 13.8V and 14.4V mean VDC depending on RPM with 0.5V residual ripple voltage, i.e. an oscilloscope shows between 13.55V and 14.05V on the lower end and between 14.15V and 14.65V on the upper end with a frequency four times the RPM. This is fairly "smooth". The question is why the Orion DC-DC Charger is not able to handle that input? And if not, how "smooth" must the input voltage be? In theory, a properly sized capacitor and a resistor should do the job and serve a low-pass filter.

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