AntarcticPilot
Well-Known Member
The reason for thick cables is to minimise the resistance and so equalise the load/draw on each battery. Nothing to do with current carrying capacity.
Do domestic batteries have to be close to each other to be in a bank?
- Thread starter Thresher
- Start date
geem
Well-Known Member
You can now buy battery balancers quite cheaply for all battery voltages. I would not worry if you can not get the batteries located next to each other. Wire up a battery balancer and you can have batteries where you like. The balancer will monitor the battery voltages and send amps to the lowest voltage battery in the bank from the battery with the highest voltage.
LittleSister
Well-Known Member
The alternator will send more amps to the lowest voltage battery of a pair. What is the added value of the balancer?
If two batteries are in different locations, and the cables of sufficient size, then the differences in charge received will, I think, be negligible, and the different rates of discharge into loads of no great consequence. Again, what is the advantage of a battery balancer in such a situation?
geem
Well-Known Member
The way I read the ops post was that he will have two domestic batteries of different types wired together but in different locations. One battery is likely to be dominant over the other in terms of charge acceptance and draw off of amps. Balancing the batteries to maintain the same voltage will extend the life of the batteries.
LittleSister
Well-Known Member
Assuming the cables are of adequate size, will the difference in voltage not be negligible?
(Particularly bearing in mind that once the batteries are almost fully charged, the current will be tiny and therefore the resistance of the cables minuscule, and in turn the difference in voltage seen by each of the two batteries as god as identical.)
I am particularly interested in explanations/justifications, rather than just claims this or that is OK or undesirable.
gregcope
Well-Known Member
This is how my design works as well.
Thresher
Well-Known Member
The B2B goes between the lead acid battery and the LiFePo4 battery?
gregcope
Well-Known Member
Yes. A B2B will have a charging direction and associated profile.
When mine sees the alternator charge the start battery (banner AGM) it will then charge the lifepo4. Mine does upto 30A. The alternator is standard.
gregcope
Well-Known Member
Forgot to add that the B2B also fires up when the Solar is charging the AGM start battery as it assumes the high battery volts is the engine. We have 110W of solar on MPPT regulators to charge the starter. It is this way as I cannot change their profile. There are other pannels that are on a LifePo4 profile MPPT.
To be fair the B2B out powers the solar MPPTs as it tired to charge the lifepo4 at 20A which is more than the solar supplies. This cycles on/off during sunny days.
My lifepo4 is disconnected when off the boat as I want to store it around 60% SOC for longevity.
When on board seems to work well as solar keeps up with load in the summer. Lifepo4 is great as it readily accepts charge and does not have the FLA charge amp acceptance limits so os much better at harvesting solar yield during a whole day.
To be fair the B2B out powers the solar MPPTs as it tired to charge the lifepo4 at 20A which is more than the solar supplies. This cycles on/off during sunny days.
My lifepo4 is disconnected when off the boat as I want to store it around 60% SOC for longevity.
When on board seems to work well as solar keeps up with load in the summer. Lifepo4 is great as it readily accepts charge and does not have the FLA charge amp acceptance limits so os much better at harvesting solar yield during a whole day.
sailaboutvic
Well-Known Member
there is a school of thought where both LA and lithium are charged to gather straight from the alternator,
without a B2B or external regulator.
by Extending the charging wire from the alternator for a much longer wire which cause more resistance and stop the alternator over heating .
ive not try it but a couple of cruisers I know are charging in this way and so far their alternator hasn’t over heated .
without a B2B or external regulator.
by Extending the charging wire from the alternator for a much longer wire which cause more resistance and stop the alternator over heating .
ive not try it but a couple of cruisers I know are charging in this way and so far their alternator hasn’t over heated .
William_H
Well-Known Member
What you write is correct when one battery has begun to fail or is very old. I think however mostly ok batteries of different ages. Vital to be able and willing to separate batteries so you can test and use individually to identify a battery failure. ol'will
coopec
N/A
I bought one of these Battery Load Testers the other day as I thought I had destroyed a battery. (happily I hadn't)
My Son (HD Diesel Fitter) says it is an el Cheapo. Would you have any misgivings using it in a situation like mine?
geem
Well-Known Member
I think with batteries in parallel, you are correct. The individual batteries will share the same voltage when sat at rest. My situation is a little different as my batteries are in series. 4x Trojan 6v batteries to make a 24v bank and 2 x12v starter batteries to make a 24v starter bank. In series they don't self balance. The battery balancers do that for me