New batteries

[Allan]

After much debate, some of which was on this forum, I have decided to to change my domestic batteries. I have a start battery which is separate and charged from one side of the alternator split charger. I have a Sterling mains charger which charges start and domestic batteries but is not used very often. Most of the charging is done by the alternator and a Rutland 913. I also have a small solar panel. My plan is to fit two new leisure batteries. They will be solid wired together. I want to do away with the 1, 2, both switch. I will also fit a battery monitor.
I have some questions:
1. Which monitor should I fit?
2. What switch should I use?
3. Should I use some sort of charge relay?
Any ideas?
Allan

 

[mitiempo]

Allan
To make it easy you can use the 1/2/both/off switch with no ill effects. It will save money as well as not leave you with a hole to fill - best bet any new switch would be a different size anyway. But don't run the charging wires through it. Easiest solution is to get an ACR (automatic charging relay) of some type. Blue Seas makes a good one but I'm not sure of the selection in your neighborhood. All charging goes direct to the house batteries (your new bank of two). The ACR takes care of the other battery. When a charge circuit is sensed it opens to allow the other battery to be charged - when the current drops it closes automatically to isolate the batteries. I'm not calling the other battery a start battery for a reason. Leave the feed wires to the starter and house breaker panel connected to the 1/2/all/off switch. The easiest way to use it is to turn to 1 when you're aboard and off when you leave. The house batteries can start an engine very easily and that leaves the other battery as a charged "emergency battery". If you wish you can start with the single battery and switch to 1 for house loads but it isn't necessary and adds complication. In any case because the alternator (and all other charge sources) go direct to the house bank no damage will ever result no matter what you do with the switch.

Probably one of the best monitors on your side of the Atlantic is the Victron BMV-600. It's a single bank monitor - the BMV-602 monitors 2 banks, but the extra expense isn't really necessary. The other (start) battery either will get little use or will only start the engine. With the main switch in position "1" you aren't using it anyway.

Make sure you use good size cabling.

Hope this helps.

 

[Allan]

Sorry, you have not understood my question. This is just a domestic installation. The start battery is mounted in the engine compartment and is completely seperate. The two domestic batteries are, at present, connected to the 1, 2, both, off switch. At present the wind turbine is only connected to one of the batteries, unless I leave the switch on both. I carry a set of jump leads to connect the start and domestic batteries in an emergency.
Allan

 

[mitiempo]

Allan
If you eliminate the 1/2/both/off switch you will have to replace it with 2 switches - one for the domestic batteries and one for the start battery. You stated that the new batteries will be solid wired together. That makes them one larger battery . You asked if you should use a charging relay. I agree as it's the best way to charge 2 banks (domestic and start). With what I suggested you will never have to use the jump leads. Both the start battery and the domestic batteries will charge off the alternator. wind turbine, or the solar panel without any switching required. While most manufacturers used to wire the charging through the switch (some still do), it's done to save money as then they don't have to install charging relays. But no charge should go through it. This is a simpler system - less confusing to use and reliable.

 

[Allan]

Many thanks for your efforts but again I have not made myself clear. Please forget the start battery. It has a switch, it is seperate, it is nowhere near the two domestic batteries, it is in good condition, it is charged by the engine (one side of the split charge) and will not be affected by the changes I am about to make! The two exsisting domestic batteries are in the battery box and connected to the 1, 2, both off switch.
Allan

 

[LadyInBed]

two new leisure batteries. They will be solid wired together. I want to do away with the 1, 2, both switch. I will also fit a battery monitor.

2. What switch should I use? - As the two new leisure batteries are solid wired together, you only need a switch to disconnect them from the domestic equipment. You might as well continue to use the 1, 2, both switch as an on/off switch. If you want to avoid confusion, you could connect position 1 and 2 together so you can switch it either way.
3. Should I use some sort of charge relay? - You already have an alternator split charger, so I wouldn't have thought you need one.

 

[Plevier]

This is not a recommendation, it is a question.
Have you looked at the Smartgauge monitor? It seems to get good reports and is apparently being used by the MoD in military vehicles..
I am intrigued by it. It has only a voltage connection, not current, so only one variable and conventionally one would dismiss it. However they insist it is not working as a voltmeter. Talking to their reps at exhibitions I have been unable to get any coherent explanation of how it works.
After a lot of head scratching, I can only think that it is using time as the second variable and is measuring rate of change of voltage with time. Difficult to do with enough accuracy I would have thought.
If you imagine a set of discharge curves, theoretically a voltage plus gradient (i.e. rate of change of voltage with time at that point) fix you uniquely on the curves and a look up table could give you your state of charge.
Brian you seem to have studied lots of monitors, have you encountered this device?
Does anyone else know if my surmise is on the right track?
Be careful with their website, it has some glaring errors on other pages!
http://www.smartgauge.co.uk/smartgauge.html

 

[mitiempo]

Hello Willow
No, I`ve never come across one of these. You must be on the right track because without a shunt there would be no other way to do it as far as I can see.I think if I wanted to know only one piece of data about my battery it would be amps in and out. Voltage as you know doesn`t tell the story until after a good rest and that`s the reason for an amp measuring meter. While they all give voltage as well that can be had by itself for not much money. At 145 pounds it`s not cheap though. I see what you mean about glaring errors. They recommend wiring the alternator to the main switch still I noticed and there are probably a few other pieces of wrong info there. When I have time I`ll take a better look. What does the Victron BMV-600 sell for over there. It`s a great monitor and if you need it they have better customer service than Xantrex - at least over here.
On another note ConaChair in the other thjread has a BEP monitor. I looked at their website and read the manual. I can`t believe such a thin manual for a meter! It explains how to hook it up but really says nothing about battery charging, bulk, absorption, float, cef, or peukert. No explanation at all.
cheers

 

[Plevier]

Voltage as you know doesn`t tell the story until after a good rest and that`s the reason for an amp measuring meter.

That's if you are attempting to deduce SOC from OC voltage, which we all - including the SmartGauge people - agree is not much use. Here they are measuring voltage under load; normally that would be useless but if they are also getting the gradient at that point with enough accuracy, maybe it could work.

The Victron is around £145 too. You'd think the SmartGauge could be cheaper with no shunt needed. Microprocessor and display cost must be similar.

 

[mitiempo]

Willow
Over here the Victron comes with a shunt as do all the Xantrex monitors. Maybe not over there?

I found this on the Smartgauge site under FAQ. They state that you cannot get actual SOC from voltage or even specific gravity and describe the errors this can lead to then they say this:

 

[Plevier]

Brian

Yes the Victron includes a shunt. I meant that one might expect the SmartGauge to be cheaper than the Victron as it does not need a shunt, but in fact it is not any cheaper.

I'm not sure what point you are making by quoting the SmartGauge website? I think maybe you are misreading it if you think they are discrediting their own device. It is badly written, but what they are saying is that you cannot get SOC from a single instantaneous measurement of voltage or even sg... (and we would both agree with this wouldn't we!).

In the previous paragraph they stress that the SmartGauge is taking continuous measurements and has to do so to work and must not be disconnected even briefly.They are making the differentiation between the continuous measurement and the taking of a single reading.

In another place they say words to the effect that the longer it is connected the more accurate it becomes - it learns. I think this supports my assumption that they are in effect by observation modelling the discharge curve - indeed a spectrum of discharge curves at different rates - for the battery. An accurate reading of V and (dV/dt) gives you a unique point in this spectrum which you can read across to SOC. (dV/dt can't be measured directly of course, it must be a predictive algorithm based on the readings during the preceding time interval). I think it's an elegant idea but demanding to implement.

I haven't worked out how they detect full charge though as you are then dealing with an imposed voltage.

 

[mitiempo]

Willow
The part I found interesting in my quoted piece was:

"This is what amp hours counters do. This is what Smartgauge does. They do it in completely different ways, but they both calculate the final figure."

I read it quickly and took this to mean they measure amps in/out somehow. I agree you need a history and in fact they state that if you unplug for 10 minutes you would miss 12 million calculations.

My error
Brian

 

[William_H]

Battery wiring

I would suggest that if you already have the 1,2,both switch in place and it will leave a hole if you remove it then connect the 2 large domestic batteries via this switch. You would almost always use it on both but it would give you the option of isolating one battery from the other for determining the condition of both when near the end of their lives.
For simplicity use your split charge system from the engine alternator to charge engine and domestic batteries. Then just connect the solar wind and shore power to the domestic batteries. Engine battery should be OK with just engine charging and starter discharging. good luck olewill

 

[mitiempo]

William
While I suggested keeping the switch I would parallel the batteries as one bank which I believe Allan was planning according to his post. A larger bank is more efficient than 2 smaller ones and the batteries will likely last longer as they will seldom be taken down as far as if they were separate. One big bank will always trump 2 smaller ones with the exception of a separate start battery which Allan has.

 

[Allan]

William, many thanks for your reply, that was my first thought. The only problem being that when I leave the boat and turn off the power, I seperate the domestic batteries and, without some sort of device, the wind and solar chargers only go to one battery or none if connected after the switch. Since asking the question I have seen that a single switch, similar to the engine battery, is less than a tenner. So that is probably what I will fit. For testing I can just remove wires from the battry posts.
I now need to decide on the monitor nobody, so far, has mentioned the NASA unit.
Allan

 

[Sybaris]

Willow3,

Brian you seem to have studied lots of monitors, have you encountered this device?
Does anyone else know if my surmise is on the right track?
Be careful with their website, it has some glaring errors on other pages!
http://www.smartgauge.co.uk/smartgauge.html

I have looked at their site a few times over the last week and am a bit confused at times. I got the feeling that the bulk of information was sort of hiding something but I have to say that I have started to change my mind, especially regarding the Smartgauge.

I did some searching on google and found some interesting links with many happy Smartgauge users.
This link http://www.panbo.com/forum/2009/03/battery-status---does-anything-work.html was very interesting and it then linked me to a canal boat forum which has a lot of information on the Smartgauge, and also plenty of good input from the inventor.
Here is an example http://www.canalworld.net/forums/index.php?showtopic=23307&hl=smartgauge&st=0

I have to say that I am tempted to try one out, and reading all the gauging discussions on their site the shortcomings of an amp gauge is very clear. The only way for an amp gauge to be near to a true value is if you synchronize it manually on a very regular basis. The smartgauge is built on a totally different model and deserves a serious look.

Cheers,
Per

 

[Mudplugger]

William, many thanks for your reply, that was my first thought. The only problem being that when I leave the boat and turn off the power, I seperate the domestic batteries and, without some sort of device, the wind and solar chargers only go to one battery or none if connected after the switch. Since asking the question I have seen that a single switch, similar to the engine battery, is less than a tenner. So that is probably what I will fit. For testing I can just remove wires from the battry posts.
I now need to decide on the monitor nobody, so far, has mentioned the NASA unit.
Allan

Allan,
Had the Nasa bm on my last boat (w33 ketch) and also installed on present one, Have never had a problem with either and it does what it says on the box....a fairly simple bit of kit to understand and install, gives Volts, Amps in, Amps out and time to go. Makes keeping a check on batt status almost automatic.

 

[mitiempo]

Allan
Your 2 new batteries should be in one bank, not two banks. You have a dedicated start battery so there is no advantage at all to separating them. But there are advantages both in ease of use, ease of charging, and battery life. You're concerned about your charging with wind and solar when away. Here's the solution: Install a charge relay between the new bank of 2 batteries and the start battery. Run your solar, and wind devices to the new bank - not through the switch as there's absolutely no reason to do so. I'd run the alternator to the new bank as well, but that's optional as with a good charging relay it's output will go to the new bank anyway. As far as switches you can keep the one you have or replace it with 2 - one for start and one for the new bank. But you do need a way to shut off both banks. With 2 switches when you're on the boat turn on the new bank. when you leave shut it off. When you want to start the engine turn on that switch. Charging from all sources is totally automatic to all batteries with no switching required for you. Add the monitor of your choice.
There is absolutely no reason to run any charging sources through the switch (or switches). Why would you ever not want to charge the batteries?

 

[Plevier]

Sybaris
Interesting reading the stuff by "Gibbo". Lots of very good sense there although as you say his manner can be a bit off!
I still say parts of the Smartgauge website are quite wrong notably the Peukert explanation. However I would guess it's the explanation rather than his knowledge, in any case I'm sure it will only affect the estimate of discharge time remaining, not the charge.
I note he's now sold out to Merlin. My impression is that they got the MoD contracts.
However I've still found NOTHING to explain how it works; have you?
There is a post from someone else suggseting it's sweep frequency AC impedance but I'm dubious. I don't think you can use that under load.
Good luck if you get one!

 

[mitiempo]

Willow
We're following each other around. I was on the panbo site last night as well as the canalworld forum. I came across this link on panbo about methods of measuring battery capacity. You might find it interesting.
http://www.buchmann.ca/article25-page1.asp