DC-DC Charger/battery charger connected direct to battery

navillus

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Feb 11, 2021
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55
I was planning to wire my renogy 20amp DC-DC charger directly to the house battery terminals, the same for my shore power battery charger. I have one 206AH lithium battery. However, I have found a couple of schematics online showing the DC-DC charger and battery charger connected to the positive and negative bus bars. Will wiring these devices to the bus bars still transfer the power un-obstructed to the battery? Or will there be unforeseen issues doing this? I am new to wiring and electronics and looking for a concrete answer on this. Thanks
 

mikefitz

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May 28, 2020
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Electrically its the same connecting directly or using buss bars , ( providing the correct gauge of cable is used for connections).
The practical limitations are that multiple connections to a battery terminal may/will exceed the capacity of the bolt or stud connection point and over stress the mechanical fixing. Its difficult also to 'stack' terminations as each termination and cable needs exit space. The usual result of trying to make multiple connections is an unreliable system with possible failure.
Its good practice to limit the number of terminations to a stud/bolt to two cables and ideally only one cable.

A further point is for safety and a need to meet codes and regulations, there needs to be over current protection for all circuits connected to the battery. This protection needs fuses or circuit breakers as close as practical to the battery. In practice a fuse/breaker between the battery positive and positive buss bar is used. As for the battery negative its useful to to have a current monitoring shunt in the path, this connects between the battery negative post and the negative buss bar.
typical use of buss bars, note the fuse at the battery positive post
fuse block 3.jpg
Incorporating high current fuses with the positive buss bar
fuse block1.jpg
fuse block 2.jpg
Mike
 
Last edited:

navillus

New Member
Joined
Feb 11, 2021
Messages
55
Electrically its the same connecting directly or using buss bars , ( providing the correct gauge of cable is used for connections).
The practical limitations are that multiple connections to a battery terminal may/will exceed the capacity of the bolt or stud connection point and over stress the mechanical fixing. Its difficult also to 'stack' terminations as each termination and cable needs exit space. The usual result of trying to make multiple connections is an unreliable system with possible failure.
Its good practice to limit the number of terminations to a stud/bolt to two cables and ideally only one cable.

A further point is for safety and a need to meet codes and regulations, there needs to be over current protection for all circuits connected to the battery. This protection needs fuses or circuit breakers as close as practical to the battery. In practice a fuse/breaker between the battery positive and positive buss bar is used. As for the battery negative its useful to to have a current monitoring shunt in the path, this connects between the battery negative post and the negative buss bar.
typical use of buss bars, note the fuse at the battery positive post
View attachment 55305
Incorporating high current fuses with the positive buss bar
View attachment 55306
View attachment 55307
Mike
Thank you so much!!!! Not only is this the information I am looking for, but you also presented it in a manner that a complete noob can understand. I really appreciate your time. Thank you again!!!
 

David_1

New Member
Joined
Jul 8, 2021
Messages
5
I was planning to wire my renogy 20amp DC-DC charger directly to the house battery terminals, the same for my shore power battery charger. I have one 206AH lithium battery. However, I have found a couple of schematics online showing the DC-DC charger and battery charger connected to the positive and negative bus bars. Will wiring these devices to the bus bars still transfer the power un-obstructed to the battery? Or will there be unforeseen issues doing this? I am new to wiring and electronics and looking for a concrete answer on this. Thanks
can you share your links for B2B chargers ? please
 

navillus

New Member
Joined
Feb 11, 2021
Messages
55
Electrically its the same connecting directly or using buss bars , ( providing the correct gauge of cable is used for connections).
The practical limitations are that multiple connections to a battery terminal may/will exceed the capacity of the bolt or stud connection point and over stress the mechanical fixing. Its difficult also to 'stack' terminations as each termination and cable needs exit space. The usual result of trying to make multiple connections is an unreliable system with possible failure.
Its good practice to limit the number of terminations to a stud/bolt to two cables and ideally only one cable.

A further point is for safety and a need to meet codes and regulations, there needs to be over current protection for all circuits connected to the battery. This protection needs fuses or circuit breakers as close as practical to the battery. In practice a fuse/breaker between the battery positive and positive buss bar is used. As for the battery negative its useful to to have a current monitoring shunt in the path, this connects between the battery negative post and the negative buss bar.
typical use of buss bars, note the fuse at the battery positive post
View attachment 55305
Incorporating high current fuses with the positive buss bar
View attachment 55306
View attachment 55307
Mike
The fuse between the positive terminal and the positive busbar, should be large enough to cover the entire load of the system? Why does there need to be a fuse between the battery and busbar if there are fuses between the busbar and all the different devices? Also, the fuses between positive bus and inverter, solar charge controller, fuse block,battery charger, DC-DC charger, should be as close to the device as possible or close to the busbar (closer to the battery)?
 

David_1

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Jul 8, 2021
Messages
5
I always work on the theory the fuse should be as small as you can get away with... yes it might blow.. but it keeps you safer.. the Fuse is there only for the wires and to stop FIRE ... use the correct fuse or smaller... Never go bigger without knowing wire sizes !
 

navillus

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Joined
Feb 11, 2021
Messages
55
I always work on the theory the fuse should be as small as you can get away with... yes it might blow.. but it keeps you safer.. the Fuse is there only for the wires and to stop FIRE ... use the correct fuse or smaller... Never go bigger without knowing wire sizes !
Thanks. So it should be big enough to deal with the max potential load of the system. My inverter fuse is 350amp, the battery to the bus bar should be the same?
 

David_1

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Thanks. So it should be big enough to deal with the max potential load of the system. My inverter fuse is 350amp, the battery to the bus bar should be the same?
I do not think I am best suited to answer this, A fuse is to protect you, but the Fuse size is based on the current the wire can carry or on the power an electrical device can use before it lets out the magic smoke... 350 amp inverter .. I would rather someone who knows more than me help :)
 

HRTKD

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Apr 24, 2020
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I do not think I am best suited to answer this, A fuse is to protect you, but the Fuse size is based on the current the wire can carry or on the power an electrical device can use before it lets out the magic smoke... 350 amp inverter .. I would rather someone who knows more than me help :)

Let's take a step back and confirm that you have an inverter that can pull 350 amps. Your battery is rated for 206 Ah. There may be a mismatch there.
 

navillus

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Feb 11, 2021
Messages
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Let's take a step back and confirm that you have an inverter that can pull 350 amps. Your battery is rated for 206 Ah. There may be a mismatch there.
Yes, you are correct. The 206Ah SOK battery has a max discharge rate of 100 amps. I plan on purchasing a second one, however have not yet. Another forum member said I could downsize the breaker between the inverter and battery at 100 amps to prevent the BMS from kicking in. I can change the breaker when I install the next battery. Also, would it be necessary to put a fuse between the inverter and busbar and another between battery and busbar, or is this overkill? Thanks.
 

HRTKD

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Somewhere South of Denver
Standard practice is to have a fuse on each cable. We fudge this sometimes, but not for the battery and inverter cables.

I vaguely remember reading that abruptly cutting off DC power to an inverter isn't a good idea. Better to limit the inverter itself that to cut off the power. I could be wrong.
 

A.Justice

Swears he didn't start that fire.
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TN
I vaguely remember reading that abruptly cutting off DC power to an inverter isn't a good idea. Better to limit the inverter itself that to cut off the power. I could be wrong.
My 12 volt inverter can pull 150+ amps from my batteries, I wouldn't want to try and "hot plug" that amount of current. I would think that switching off AC loads first, then the inverter would be the better idea.
 

navillus

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Feb 11, 2021
Messages
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Standard practice is to have a fuse on each cable. We fudge this sometimes, but not for the battery and inverter cables.

I vaguely remember reading that abruptly cutting off DC power to an inverter isn't a good idea. Better to limit the inverter itself that to cut off the power. I could be wrong.
Ok, Gotcha. would you place a fuse closest to the battery terminal then a cut of switch, or the other wat around?
 

Zwy

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Jan 3, 2021
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Ok, Gotcha. would you place a fuse closest to the battery terminal then a cut of switch, or the other wat around?
Fuse always first. The cut off switch could fail by overheat, loose connections and even arcing internally in a case of a dead short after it. With the fuse past the switch, there is no protection on anything ahead of it except for the BMS.
 

navillus

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Feb 11, 2021
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Fuse always first. The cut off switch could fail by overheat, loose connections and even arcing internally in a case of a dead short after it. With the fuse past the switch, there is no protection on anything ahead of it except for the BMS.
Thanks!
 
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