FAQ

Temptress DIY Air Conditioner FAQ

Q:How do I calculate how many BTUs I need to cool a space?

A:A general rule for determining appropriate cooling capacity is 14 BTU/cubic feet. Use the 16 to 19 BTU/cubic feet formula to calculate suitable cooling capacity for areas that get a lot of sunlight during the day (such as salons), especially if the deck is not shaded or well insulated. For below-deck areas that are primarily used after sunset (such as cabins), use the formula for 10-12 BTU/cubic feet to get an appropriate cooling capacity.

 

Q:I have a 24V and 12V system onboard. Do I need the voltage converter or can I wire it directly to 24 volts?

A:The compressor and driver board are 24V, while the rest of the components are 12V. A 24V pump and evaporator are available via special order. The voltage converter would not be required, making the system more efficient.

 

Q:I have watched Clark's video, but that is not to say you are selling the same components he used, such as the titanium condenser and the compressor Clark shows in his video.  

A:We use the same titanium condenser and compressor that Clark shows in his video. FYI, the compressor driver board has been updated since that video was made.  Here is a link to the specifications page.  https://marinedcac.com/pages/component-size-specifications 
 

 Q:Is the DC compressor US made?

A:The DC compressor and driver board is made in the USA.
 

Q:How many BTU's is the compressor rated at? 

A:Typical usage is 3K BTU. The system can provide up to 4K BTU.  See the specifications page for all of the details.  https://marinedcac.com/pages/component-size-specifications
 

Q:How much power does the system use at full speed on the compressor, and including the water pump?

A:3K BTU at about 180 watts.  4K BTU at about 255 watts. See the specifications page for more details.  https://marinedcac.com/pages/component-size-specifications
 

Q:What water pump are you using?

A:Johnson 12V pump
 

Q:I see you have a filter/dryer, but does the system have a receiver? 

A:The system doesn’t require a receiver.  
 

Q:How much refrigerant is typical, realizing the tubing runs will change this slightly?

A:Our bench setup uses less than a pound of R134a.  The distance between the evaporator and condensor will affect the amount of refrigerant required.  We have tested systems that are up to 10' apart.
 

Q:Do you foresee any problems with getting R134 in the future? I know it's being phased out.

A:We will modify our system to accommodate whatever refrigerant becomes the standard for marine use. 

 BankManager™ FAQ

Q: I've finished my physical install. How do I check that everything is working properly?

 A:Here is the full test procedure:
  1. Turn on the BankManager™ using the switch. You should hear it click the contactor off twice—once shortly after starting, and once again just before the splash screen goes away and the screen shows voltage. If you hear these 2 clicks, the wiring to the “off” side of the contactor is correct.
  2. The BankManager™ screen will say “Disconnected” until it sees that it is safe to connect your battery banks.
  3. When the voltage of both banks is equal (and it is therefore safe to connect), the BankManager™ will connect your Lithium bank. To expedite this:
  • If your Lead voltage is higher, turn off your charger.
  • If your Lead voltage is lower, apply charge to the system.
  1. Once the voltages of the 2 banks are equal:
    • The BankManager™ will say “Connected”
      • The blue light will illuminate and should be visible through the case.
      • The contactor will click on. Once this happens, you have verified the wiring to the “on” side of the contactor is correct.
  1. Charge your system harder than any of your normal loads would require. (First turn off loads of necessity). You should see an amp reading on the BankManager™ screen. This number should be positive. If it's negative, you have something backwards with the current sensor.

  2. Now wait until your Lithium bank is fully charged. Depending on your charge rate and many other variables, this could happen once the system voltage gets over 13.8V. If you are charging strongly, it could happen at a much higher voltage. When your Lithium bank is fully charged, the BankManager™ will display “Disconnected,” turn off its blue light, and click the contactor off. This verifies that the entire device is working properly.

Now wait until your Lithium bank is fully charged. Depending on your charge rate and many other variables, this could happen once the system voltage gets over 13.8V. If you are charging strongly, it could happen at a much higher voltage. When your Lithium bank is fully charged, the BankManager™ will display “Disconnected,” turn off its blue light, and click the contactor off. This verifies that the entire device is working properly.
Q: I just started my BankManager™ and it seems to think my lithium bank is full.  It's not.  What's up?
 A: That value is wrong on boot up.  It will start tracking accurately once you fully charge your Li bank the first time and see an asterisk (*)  after the Li voltage.  From then on, it should be fairly accurate until you power down the BankManager™.
The BankManager™ does not use that value to tell when your Li is fully charged. (And you shouldn't trust a charge controller that does.)  The percent-of-charge (POC) meter is, in its heart, a coulomb counter.  These are always off.  I tried to make the one in the BankManager as accurate as any, and it has the advantage of being automatically reset on every full charge, but I wouldn't trust the charging of your Li to it. This value is used for the “minimum discharge” setting, if you have a BankManager™ version 2.2 or later and turn on that feature.
 

Q: I'm having trouble finding shielded wire for the current sensor. Any advice?

 A: I originally over-specced the wire required. I use a “differential pair” connection, which is really robust. I just happened to have the perfect wire on my boat. Loads of people have found success by buying a piece of ethernet cable and cutting the ends off for the 4 wires that go from the  BankManager™ (GND, Vref, Vout, +5) to the current sensor. 
 

Q:  I’m confused about the whole "switch" thing (Gen2). How should I wire it?

 A: Apologies, the original manual did not explain this clearly. We have since updated the manual with a clearer diagram. In short:

  1. Run a good big wire (12 gauge) from your Li negative terminal to one terminal of a simple on/off switch. 

  2. Run 2 more wires from the other terminal of the switch to the  BankManager™ GND screw terminal, and to the current sensor.

Q:  How big/small can my batteries be?

 A: Your battery banks can be any size, and in any ratio, but there are some rules. 

  • If you don’t want to use your lead on a daily basis, your lithium battery bank should be big enough to last from when your daily charging ends (e.g., sundown, in the case of solar-based systems) until it starts again (e.g., sunrise). 

  • Your lead battery bank should be big enough that your system operates in a “sane” manner when the  BankManager™ has disconnected your lithium bank. Note that some charge controllers don’t operate well with small batteries attached. If you have HUGE loads that come on all at once, your lead bank needs to be able to support those loads for a few seconds without the voltage going down a lot.

 

Q: Can I use my starter battery as the “lead bank” in my hybrid system?

 A: Sure. In fact, as long as you have enough lithium battery and charge capacity in your hybrid system such that you never deplete the lithium batteries, you have a condition where you will never cycle your lead bank. (If so, having deep-cycle lead batteries with thick plates is actually just a needless expense.) In this case, you are actually better served with cheap, readily available “starter” batteries, because with their thin plates, they are better at absorbing or serving power with minimal change to their voltage. 
If you have a very large short-period load (like a windless or bow thruster) having “starter” batteries in reserve is great. Your lithium will drop in voltage when it’s asked to deliver near its limit. When this voltage drop goes below 12.8 V, the starter battery will be ready to deliver help.
 

Q: My lead batteries are old. Can I still use them?

 A: Old, sick batteries shouldn’t be used, but lead with a lot of life left in it can work fine, and will probably last for a surprisingly long time in a hybrid system. 
The test I recommend to help you decide whether your lead batteries are healthy enough is to do the following:

  1. FULLY charge your lead batteries. (I mean really, fully charged.) 

  2. Apply enough current to hold them to 13.2 V (possibly by connecting them to a lithium battery). This is the amount of power they will be eating from your lithium all night. If this amount of power draw seems manageable, then use them.

 

Q: Tell me about my version number. What features do I have, or what am I missing?

A:// Ver 1.0 Initial offering
// Ver 1.1 Initial offering
// Ver 1.2 Initial offering (each with slightly different hardware)
// Ver 1.3 added software fuse (MAX AMPS)
// Ver 1.4 Cleaned up Rotary Encoder so it operates smoother
// Ver 1.5 If lead voltage falls really fast from above li voltage to below - Connect the banks
// Default PbVoltage to high during disconnect. For very special charge controllers. (dov)
// Ver 1.6 Cleaned up Coulomb counter POC much more accurate
// Ver 2.0 New Case and Board
// Less clicking
// Set Minimum POC as a Beta test feature (MIN POC)
// Ver 2.1 Un-Asterisk on "average" liVoltage
// Ver 2.2 Fixed POC reconnect issue and made (MIN POC) a supported feature
// Cleaned up clicking (reconnect on cloudy days)
// Charge to Voltage - Soaking now works again
// Reconnect after menu improved
// Ver 2.3 Hardware change to tolerate out of spec OLED screens
// Ver 3.10 Initial offering for the Gen3 adds to the Gen2
// Ver 2.10 Control of the screen brightness (off and on)
// Un-Asterisk is now based on Percent Of Charge
// You can set a POC for when you want your li to
// be a candidate for recharge
 

Q: I’m leaving my boat for a long time, what BankManager™ settings should I use?

A: There are many right answers here. Honestly, leaving your system set the way you normally use it isn’t all that bad. It’s much easier on the Li batteries than using commercial charge controllers without the BankManager. 
If you are leaving your boat with loads (like refrigeration) engaged, then leave everything as you use it when you are there.
But, if you are removing most loads (leaving only bilge pumps or the like active) you may wish to let your lithium batteries discharge themselves to 50% and tell the  BankManager™ to maintain them there. This can be achieved by doing the following:

  1. Set the CHARGE TO menu setting to 50%

  2. Set the RESET FULL BATTERY menu setting to 12.9V

  3. for version x.10 set the RESET FULL BATTERY to something like 30%

(It would be best to set this up while you still have loads. This will expedite the discharge of your Li bank to closer to 50%.)
This will tell the BankManager™ to let your Li bank drop to below 50% and only charge it back up to about 50%. Assuming your batteries aren’t being discharged much, they will likely only see a charge cycle at very long intervals (likely months).
If you leave the system for a VERY long time push the reset button every 6 months or so for Gen3
 

Q: What benefits can the  BankManager™ offer, beyond letting me add lithium batteries to my lead system? (~ Patron John F.)

A: There are many benefits to mixing battery chemistries within the same system. These include safety, financial savings, durability, redundancy and the ability to charge your lithium batteries properly. 
Because of our work in this field, we were asked by The International Organization for Standardization (ISO) to write up a white paper to help them develop a new standard for hybrid off-grid battery systems (See our ISO Proposal here). This document goes into great detail about the advantages of hybrid battery systems. Once the ISO finishes their standard, it’s very likely that the  BankManager™ approach will meet this requirement. 
The American Boat and Yacht Council (ABYC) currently has a requirement that any lithium battery system installed on a boat “shall” have a backup power system for all critical systems. A hybrid battery system meets this requirement in a manner that is utterly transparent—If your lithium bank fails, your system simply drops a tiny bit in voltage and the lead batteries provide power.
The most unique thing about using the  BankManager™ to manage your hybrid battery bank is how it charges your batteries. With the  BankManager™, most of the charge current goes into the Lithium first. Once the BankManager™ senses the lithium bank is fully charged  to the operator's desire (as set in its menu), it disconnects the lithium bank from the system and allows the system’s charge controllers to continue to charge the lead batteries. 
It is vital to the health of the lithium batteries that they are removed from charge once full, or they are prone to “low current overcharge” which causes a slow but irreversible damage. It’s also very important to fully charge the lithium batteries, as they are prone to “memory,” (though it seems that can be cleared over time). Only the  BankManager™ protects your new, expensive lithium batteries from these things, and offers them the chance for a longer life. It does this by using a complex mix of voltage, current flow, time and history of the battery. This is in stark contrast to other charge controllers, which rely solely on voltage measurements to decide when the lithium batteries are full.
Remember, if you leave your boat in a cold place and your batteries don’t protect from charging below 0°C, it’s probably best to just leave them without a charger at all. Charging even a little bit when below freezing can kill lithium batteries!
 

Q: How will the  BankManager™ approach affect my battery life?

 A: That question has two sides to it, since we have 2 different types of batteries in our hybrid battery system. Let’s compare each type of battery to how that battery would fare alone in a typical installation.
LITHIUM (LiFePO4) - In a typical installation, the lithium is charged by various charge controllers, all using basically the same algorithm. They charge as if they were charging lead, but set the absorption time to 0. This means each charge cycle, the lithium cells are charged to a set voltage, then allowed to drop to a lower voltage where they are “floated”. 
Lithium batteries can’t safely be charged to a voltage unless they are charged at a constant current, and a constant current is impossible to achieve with solar (clouds and sun angle changes) or in a system in daily use. For example, when a device like a refrigerator comes on, it changes the amount of current available to charge the batteries. This leaves the lithium cells either undercharged (which causes memory to form) or overcharged (which causes slow, irreversible cell death). Floating at any voltage over 13.48V for a 12V setup causes the same slow cell death. We call this “low current overcharge”.
With the  BankManager™ the lithium batteries are charged accurately to the point you choose, and then removed from the system until their power is required. The BankManager™ is so accurate at this it’s safe to set the charge goal to 100% so no memory is formed. WIth a BankManager™, the batteries are being charged as well as we know how to charge them, with no shortcuts. This should allow your lithium batteries to see their true 4000-cycle life.
LEAD BATTERIES - In a typical lead installation, the lead batteries are charged each day and used each night. If there is enough power and time available, they may be charged fully. But since lead is hard to charge the last 15 or 20 percent, this often takes more time than is available, so the lead is not fully charged. Not fully charging lead batteries shortens their life considerably. But the simple act of using the lead batteries also shortens their life. Lead is only good for about 400 50% discharge cycles. Lead batteries just don’t last as long as lithium batteries.

With the  BankManager™, your lead bank will likely not be used much. It’s there to help with large current pulses and to be backup power if there are several days without charging. But mostly it is there to keep your system going while your chargers are still producing power but the lithium is fully charged and disconnected. In fact, the lead will be held up to the low, 13V range all night while the lithium is being used to run your system. It’s like the “float” charger you might put on your sports car during the winter when you don’t use it. Because your lead bank will very rarely be used within a system with a BankManager™, it should see a very long life.

Q: My BankManager is not connecting my lead and lithium banks. It should be, but it’s not. How can I fix this?

A: The BankManager will only connect your Lithium bank with the rest of your system when the voltage in both the Lithium and the Lead side are very close. 

  • If you are currently charging your system and your lead bank is at a higher voltage than your lithium bank, turn off your charge source until the voltages come together. Then the BankManager™ will connect.  

  • If your lead bank is lower in voltage than your lithium bank, charge your system a bit until the lead voltage comes up. Then the BankManager™ will connect.

This is a key feature of the BankManager™. It’s important because if the voltage of your banks are different, you may be in a situation where, if connected, one bank will quickly discharge into the other.  This could be dangerous if the current generated is larger than your system can safely handle.

Note that for a solar-charged marine system, it’s better to make BankManager™ menu changes in the morning rather than in the evening. This is because after you confirm a setting change in the menu, the BankManager™ will be in disconnect mode. If there is a voltage disparity between the Lead and Lithium, the BankManager™ will not reconnect on its own. If it’s in the morning and the sun is up, you can simply turn off your solar charge source for a bit until the voltages are the same. But if the sun has already set, you’d have to start your engine to get the voltages to align. Either approach will work, but I find the morning approach to be more convenient.

Q: Why use the bank manager instead of a DC-to-DC charger like Victron’s?

 A:There are two reasons:

  1. There are no DC-to-DC chargers out there that charge  Lithium correctly for long life. Much like all the "lithium" MPPT solar controllers, these DC-to-DC chargers are just charging Lithium as if it  were lead, but with a short or “0” absorption period.  Lithium Is a different beast than lead, and can't safely be charged to a voltage. Lithium also can't safely be held at any voltage over 13.48V.

  2. The whole idea of a DC-to-DC charger is suspect. It solves some issues like current control (I use one in my truck camper to keep the engine charge rate to 20A, because of wiring size). But at what cost? 

    • The DC-to-DC charger limits current from your alternator. Though that works, there is a better way to solve the problem—airflow or regulators. 

    • It's one directional, and can't move power back to the lead side. 

    • It loses lead support for big loads. 

    • Your lead isn't floated by your Li.

In contrast, the BankManager™ brings the two battery chemistries together, so you get the advantages each type of battery has to offer. The BankManager™ approach gives the opportunity for you to see the longest possible life from each battery.
 

Q: My lithium battery stopped taking a charge, but my BankManager™ still says it’s connected. What's going on?

A:Most likely, the BMS inside your battery shut down the charging process because one or more of that battery’s cells is way out of balance. (If your battery has a working balancer this is unlikely to happen unless it's a new battery or you have been charging it slowly for a long time and recently charged it very quickly.) In short, you need to balance your cells. 
Talk to your battery provider if necessary, but generally speaking, the way to balance your cells is to find the voltage where the battery stops taking a charge.  And charge to that voltage repeatedly0. To do so, you can:

  1. Set the BankManager™ to “Charge to Voltage” mode and let it run through some cycles.

  2. Raise the voltage little by little each cycle. If the lithium shuts down early again, back off the voltage a bit.

If you have an easily-opened battery, or just want to open them, then adding an inexpensive “active balancer” might be a really good upgrade.