Inverter cabling question

[Helmsman]

Ok. I installed a new Promariner 2000 PS inverter charger last year. Well, I did some of the work, and the “main electrical guy” on our lake did the rest. In order for the alternators to charge the battery while underway, I replaced the two alternator three battery bank diode charger with ProIso 2 alt 4 battery version. The alternators put out 100 amps a piece. Promariner said the circuit must be able to handle 200 amps, the total of the two alternators.

I was having trouble keeping the inverter bank (4 6 volt batteries in a 2 battery 12 volt configuration charged while underway. When I checked the voltage at the four outputs, I was getting 13.8 to 14.1 at the engine outputs on the isolator and 15.1 volts at the inverter isolator output. The other bank was not charging at the time I was checking which may or may not be ok. When I checked the voltage at the inverter battery bank, it was receiving only 12.8. When I spoke with Promariner, they told me the wire from the isolator to the inverter battery bank should be no longer than 12 feet and if that long should be 2/0. It is 13.66 feet with no way to shorten it. The wire is the same size as the wires that go to the two engine batteries (close to 10 feet), and the house battery (close to 5 feet) from the original isolator which were original installation by Carver. I think it is probably 2 gauge, but I haven’t attempted to figure that out.

Anyway, here are my questions. I am stuck with the distance. Would you advise using 2/0 on the Isolator to inverter bank, or would you go with 3/0? When I look at ABYC guidelines, it looks like 2/0 would work. If I change out the cable to the inverter bank, should I also consider changing out the cables to the two engines?

If you scroll down the link below, you will see the recommended wire sizes.

https://baymarinesupply.com/bosns_corner_wire_sizes

Thanks for any advice that could be thrown my way.

[tomschauer]

When you are taking these voltage readings do you have a heavy AC load on the inverter? If so it may be wire size. If not I would lean towards something miswired. I would verify all wiring, especially the isolators. They tend to melt when not properly configured.

[bud37]

If that wire run is 13.66 feet of straight run one way, then the effective length of that circuit would be around 27ft. You have to count the hot and ground side as a total. Choose your cable accordingly.

Remember, those 100amp alts will only put out maybe 85 to 90 amps apiece when the batteries are virtually dead.....you should still see 14.5 volts at the batteries while underway in my opinion.

[Helmsman]

Source of the post If that wire run is 13.66 feet of straight run one way, then the effective length of that circuit would be around 27ft. You have to count the hot and ground side as a total. Choose your cable accordingly.

Remember, those 100amp alts will only put out maybe 85 to 90 amps apiece when the batteries are virtually dead.....you should still see 14.5 volts at the batteries while underway in my opinion.

Thanks Bud. The way the ProIso works is that it will charge the engine batteries first. After they reach 13.3 the ProIso then moves to the next set of batteries. So the port alternator charges the port engine, then it charges the house battery. The starboard alternator charges the starboard engine, then the inverter batteries. Of course if an alternator fails, one should be able to supply all banks.

[Helmsman]

Source of the post When you are taking these voltage readings do you have a heavy AC load on the inverter? If so it may be wire size. If not I would lean towards something miswired. I would verify all wiring, especially the isolators. They tend to melt when not properly configured.

Thanks! I found that the electrician hooked the engine output to the inverter bank and vice versa last summer. I reversed those and it Was working. This testing I have been doing is to validate it is ok. The Promariner guy said that I should load test the batteries, since I was getting 15.1 volts at the isolator for the inverter bank. Since the boat is winterized, I wanted to get the proper size cables installed and get the batteries load tested to eliminate that as an issue.

[km1125]

Source of the post
Thanks Bud. The way the ProIso works is that it will charge the engine batteries first. After they reach 13.3 the ProIso then moves to the next set of batteries. So the port alternator charges the port engine, then it charges the house battery. The starboard alternator charges the starboard engine, then the inverter batteries. Of course if an alternator fails, one should be able to supply all banks.

Which unit do you actually have? Is it the "Promariner 2 alt. 3 batt Isolator number 02-130-3" ? (I didn't see a '2 alt, 4 batt version on their website). If so, there is no "the port alternator charges the port engine, then it charges the house battery. "

This is a simple diode isolator. There is ALWAYS voltage drop going through a diode isolator, so your charge rates and capabilities are REDUCED going through the isolator unless the regulator in the alternator is modified to sense the actual battery voltage. It can only do this for one battery though, so once THAT battery is "up to snuff" the charge capabilities and rates going to ALL the other batteries suffers. You can actually measure this very easily by using a voltmeter to measure the voltage drop from the input terminals (either alt terminal) to each battery output terminal. You will likely see over a volt of drop there.

There are active isolators which don't use diodes and have virtually no voltage drop that eliminate this issue.

That same comment "charges the starting battery first, then charges house" is also mistakenly used with the voltage sensing relays like the Blue Seas ones. Only if the starting battery is SO LOW that the alternator can't develop it's normal output voltage (~>13Vdc) will the relay be kept open until the voltage increases. If your start battery was that low, it probably wouldn't have started the engine but in that case the alt would charge the start battery first before the relay would activate and start charging the house.

[Helmsman]

Source of the post

Source of the post
Thanks Bud. The way the ProIso works is that it will charge the engine batteries first. After they reach 13.3 the ProIso then moves to the next set of batteries. So the port alternator charges the port engine, then it charges the house battery. The starboard alternator charges the starboard engine, then the inverter batteries. Of course if an alternator fails, one should be able to supply all banks.

Which unit do you actually have? Is it the "Promariner 2 alt. 3 batt Isolator number 02-130-3" ? (I didn't see a '2 alt, 4 batt version on their website). If so, there is no "the port alternator charges the port engine, then it charges the house battery. "

This is a simple diode isolator. There is ALWAYS voltage drop going through a diode isolator, so your charge rates and capabilities are REDUCED going through the isolator unless the regulator in the alternator is modified to sense the actual battery voltage. It can only do this for one battery though, so once THAT battery is "up to snuff" the charge capabilities and rates going to ALL the other batteries suffers. You can actually measure this very easily by using a voltmeter to measure the voltage drop from the input terminals (either alt terminal) to each battery output terminal. You will likely see over a volt of drop there.

There are active isolators which don't use diodes and have virtually no voltage drop that eliminate this issue.

That same comment "charges the starting battery first, then charges house" is also mistakenly used with the voltage sensing relays like the Blue Seas ones. Only if the starting battery is SO LOW that the alternator can't develop it's normal output voltage (~>13Vdc) will the relay be kept open until the voltage increases. If your start battery was that low, it probably wouldn't have started the engine but in that case the alt would charge the start battery first before the relay would activate and start charging the house.

It is a 2-4. ProIso makes it. The product number is 23248.

http://files.powerprodllc.com/en/~/medi ... titem=true

Look at the listing on the right of the first page at the bottom. According to the manual and also what the technical guy at ProIso told me, the isolator charges the engine batteries first. After those two engines receive 13.3 volts, it begins charging the other banks.

When I was trying to diagnose the situation, I took voltage readings at the isolator. All battery banks were fully charged from shore power. I strictly followed the instructions of the Promariner tech. He told me to attach the negative prong of the voltmeter to the negative ground of the isolator, and then test each input and output.

Alternator input 1 was 14.62, engine 1 was 14.44, inverter battery bank was 15.0.

Alternator input 2 was 14.87, engine 2 was 14.54, House battery was 12.67.

When I tested the voltage at the fuse to the inverter bank, with the isolator showing the 15.0 volts above, the reading was 12.6 volts.

What I am trying to do now is follow the suggestions of the Promariner tech to change out the cable. He stated as does the manual that the maximum length of a cable is limited to 12 feet. If that is the case, then the isolator won’t work for me and I have wasted $300 and need to start looking for an isolator which will work with longer runs, since the length to the inverter bank is 13.66 feet (not to mention the additional length to the negative ground) and the OEM equipment is probably 10 feet. It seems illogical that the cabling is limited to the 12 foot length since, in practice (including the OEM), the length from isolator to batteries, and then to ground exceeds 12 feet. It is a Carver 33 SS with batteries down the middle between the engines. I didn’t have enough room for the inverter batteries there so the electrician placed them above the water tank about 4 feet further aft.

The issue for me is whether to buy the 2/0 or 3/0 to attempt to eliminate the apparent voltage drop from the isolator to the inverter bank. I will also reach back out for them to see what they say, but thought I would pass through here for the practical experience you folks have.

[bud37]

Here is another chart to help you choose.....you are at 24 feet according to your post.

One other thing to consider is the specs of some of these devices, they are controlled at different voltages, so you need to be aware of the thresholds when wire sizing etc...there are some isolators ( mosfet/fet ) that have very little voltage drop across.


.

DC_wire_selection_chartlg.jpg

[Helmsman]

Source of the post Here is another chart to help you choose.....you are at 24 feet according to your post.


One other thing to consider is the specs of some of these devices, they are controlled at different voltages, so you need to be aware of the thresholds when wire sizing etc...there are some isolators ( mosfet/fet ) that have very little voltage drop across.


.

DC_wire_selection_chartlg.jpg

Thanks Bud. The cable from the isolator to the battery bank battery switch is 13.66 feet. Then about 6 feet through the batteries to the inverter negative feed. Then about 4 foot From the inverter positive through the fuse to the switch to the positive battery connection. So I would say about 20 to 22 feet. There is also a properly sized ground cable that goes to the starboard engine from the inverter but I don’t think that counts, does it?

[km1125]

Well, that's definitely a FET-type isolator, so that's good news.

Here's a thought. Move the ground wire on the unit over to the negative terminal on your inverter bank. This will essentially "trick" the unit into thinking that Batt1 has reached 13.3 and begin charging the other banks quicker.

Also, the instructions don't really cover much of the applications where you have two alternators. They just say that the dual alternators "connect to ALT1 and ALT2" and that the only other requirement seems to be that "ALT1 and BATT1" need to come from the same engine. Does that mean "ALT2 and BATT2" need to come from the same engine? Does that also mean in the charging sequence that it always starts with BATT1 and then goes to BATT2 and then to BATT3 and then to BATT4? Could you put your inverter bank on the BATT2 terminal so it gets the second charging sequence?

If you're struggling with the decision between going with 2/0 and 3/0, just remember that while the smaller gauge might work, the larger cable will ALWAYS result in more overall current flow and quicker charging of the batteries if there is available current at the source. The batteries only charge because of a DIFFERENCE in voltage between the source and the battery. If the battery is already at 11.7 volts and the charging source is at 13.6, then it's really only a 1.9 VDC difference that's making the battery charge AT ALL. Increasing this difference by just 1 volt is nearly a 50% difference, and every little bit helps.